Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2023.127529

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DOI： 10.1016/j.jcrysgro.2023.127552

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DOI： 10.1016/j.nimb.2023.165181

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DOI： 10.35848/1882-0786/ad120b

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DOI： 10.1117/12.3010733

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DOI： 10.18494/SAM4647

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DOI： 10.1117/12.3009947

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DOI： 10.1063/5.0177681

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DOI： 10.1063/5.0180062

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DOI： 10.1002/pssa.202200871

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DOI： 10.1109/LED.2023.3285938

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DOI： 10.1109/LED.2023.3274306

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DOI： 10.1063/5.0155363

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DOI： 10.1063/5.0149838

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DOI： 10.1063/5.0146080

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/ma16052016

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/cryst13030524

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DOI： 10.35848/1347-4065/acb74c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES  

DOI： 10.2322/tjsass.66.10

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1117/12.2657032

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DOI： 10.1038/s41598-022-25522-6

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1116/6.0002111

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DOI： 10.1063/5.0124512

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DOI： 10.1063/5.0120723

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DOI： 10.35848/1882-0786/ac9c83

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DOI： 10.1016/j.apsusc.2022.153882

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DOI： 10.1063/5.0122292

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DOI： 10.3390/ma15176165

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0088908

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DOI： 10.1016/j.jcrysgro.2022.126749

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DOI： 10.35848/1882-0786/ac79a1

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DOI： 10.1002/pssr.202200127

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DOI： 10.1088/1361-6463/ac5d03

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-022-12628-0

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-022-10610-4

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0085384

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DOI： 10.35848/1882-0786/ac6197

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DOI： 10.35848/1882-0786/ac60c7

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DOI： 10.35848/1882-0786/ac5acf

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DOI： 10.1063/5.0083194

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DOI： 10.35848/1882-0786/ac53e2

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DOI： 10.35848/1882-0786/ac481b

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DOI： 10.35848/1347-4065/ac3a1d

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DOI： 10.1109/LED.2021.3131057

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DOI： 10.1109/JEDS.2022.3208028

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DOI： 10.1063/5.0076764

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DOI： 10.1088/1361-6463/ac2065

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DOI： 10.1109/TED.2021.3119528

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DOI： 10.1116/6.0001272

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DOI： 10.1007/s00259-021-05460-7

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0077364

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DOI： 10.1063/5.0066139

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DOI： 10.1063/5.0051053

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DOI： 10.1038/s41598-021-97159-w

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s00339-021-04808-y

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DOI： 10.35848/1882-0786/ac0fb6

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DOI： 10.35848/1882-0786/ac0ffa

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DOI： 10.35848/1882-0786/ac154c

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2021.126173

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1347-4065/ac06b5

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DOI： 10.35848/1347-4065/abd538

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/abf443

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0042036

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/abe3dc

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/cryst11040356

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/abe657

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/cryst11030254

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/qubs5010005

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2021.1.0_1347

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1364/OME.420328

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/JEDS.2021.3081463

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DOI： 10.1063/5.0028516

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/abcb49

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsami.0c11883

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1364/OME.401765

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.nimb.2020.06.007

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0010774

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1347-4065/aba0d5

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/ab93a0

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1882-0786/ab9166

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssb.201900554

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2020.1.0_3111

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/jmicro/dfz037

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1116/1.5120417

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Association for Crystal Growth  

<p>  The microscopic structural and optical characteristics of AlGaN light-emitting diodes (LEDs) fabricated on the AlN templates with dense macrosteps are shown to clarify the origin of their high internal quantum efficiency of radiation (IQE). The cross-sectional transmission electron microscopy observations under the high-angle annular dark field scanning mode and microscopic energy dispersive X-ray spectroscopy revealed that the AlGaN cladding layer under the AlGaN quantum well (QW) layer had a microscopic compositional modulation, which originates from the macrosteps at the AlN template surface. Moreover, Ga-rich portions in the cladding layer behaved as current micropaths, and the micropaths are connected with the carrier localization structure formed in QWs. The in-plane cathodoluminescence (CL) spectroscopy showed a significant inhomogeneity of the CL characteristics. The gentle slopes at the sample surface showed brighter emissions with a lower peak photon energy, confirming the carrier localization. This carrier localization structure in the QWs combined with the current micropaths in the cladding layer can increase the IQE as well as external quantum efficiency of the AlGaN LEDs.</p>

DOI： 10.19009/jjacg.47-3-04

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/ispsd46842.2020.9170101

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5125623

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5097767

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/ab1250

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/ab06b9

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/ab106c

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2019.1.0_3122

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/iciprm.2019.8819270

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2018.1.0_1670

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2017.1.0_1554

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2017.1.0_1136

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.2.0_2888

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.2.0_2867

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2014.2.0_1745

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.tsf.2013.02.048

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4825124

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JC05

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JK09

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JB16

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JE07

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JE06

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JB11

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JB14

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JC04

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JE10

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.52.08JB09

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Although plasma-assisted molecular beam epitaxy(PA-MBE) is a promising technique for GaN growth,the growth rate obtained by this technique is lower than that obtained by metal organic vapor phase epitaxy(MOVPE).In order to improve the growth rate of the technique,high density radical source(HDRS) was developed.By vacuum ultraviolet absorption spectroscopy(VUVAS) measurement,two orders of magnitude higher radical density was confirmed in a comparison of the HDRS and a conventional radical source(CRS).While faster growth rate of 1.4μm/h in GaN homoepitaxy was achieved,better crystalline quality of InxGa_<(1-x)>N(x=0.03〜0.16) epilayers with approximately 1.4μm thickness were also achieved by introducing the HDRS in PA-MBE.

DOI： 10.1299/jsmeiip.2013.5

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We grew high-quality semipolar (1-101) GaN stripes on a Si substrate by selective area growth and regrew InGaN/GaN MQW on these stripes with MOVPE. The PL peak wavelength at 300 K and InGaN well thickness for the obtained samples were 435-590 nm and 2-9 nm, respectively. In PL measurements from the surface, we found that a shorter wavelength and thinner well sample have PL polarization perpendicular to the c axis. On the other hand, as the PL wavelength is longer and/or the well is thicker, the PL polarization shifts from perpendicular to parallel. In the PL measurement from the (11 -22) edge surface of the sample with shorter wavelength, we observed the narrowing of PL spectrum. In addition, the parallel component of PL polarization increased with increase in well thickness. Therefore, we can control the direction of polarization by managing well thickness and indium composition and apply to make a LD structure.

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssb.201100445

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssa.201100379

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0268-1242/27/2/024006

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Association for Crystal Growth  

(1-101) GaN and (11-22) GaN was grown by MOVPE on etched Si substrate. A characteristic of optical, electrical and impurity was evaluated on each face GaN. We also reported an Indium incorporation and a process of dislocation propagation on the (1-101) GaN in this paper.

DOI： 10.19009/jjacg.38.4_241

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.50.122101

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/APEX.4.092102

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssa.201000907

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2010.10.054

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/APEX.4.039201

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.50.01AD04

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11431-010-4182-2

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/APEX.4.012105

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.3666474

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssc.201000969

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：National Institute of Technology, Toyota College  

We have studied the residual strain and stress in semi-polar (1-101)GaN and conventional (0001)GaN grown on Si by means of Raman spectroscopy. By adopting the stress coefficients reported in the references, the residual strain of samples were deduced from the frequency shifts of the phonon modes in Raman spectra. As the results, it was found that the strain tensor of (1-101) GaN/Si was smaller than that of the (0001)GaN/Si in good agreement with the results obtained from the X-ray diffraction measurements.

DOI： 10.20692/toyotakosenkiyo.kj00005889042

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3938/jkps.54.2363

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2009.01.032

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2009.01.064

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0022-3727/42/4/045112

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Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/jmicro/dfm016

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/jmicro/dfm013

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0953-8984/19/4/046204

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2006.10.229

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.45.7655

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssb.200565115

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.45.4015

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Using a selective MOVPE method, (1-101)GaN was grown on a 7-degree off-axis (001)Si substrate. The top (1-101) surface of the sample was terminated with N, which is contrast to that the (0001) face is terminated with Ga. The doping of Si and C was attempted to control the type of conduction. A nominally undoped GaN/AlN heterostructure showed p-type conduction. The doping of Si changed the type of conduction from p-type to n-type. On the other hand, the hole concentration increased with the C doping level. These results proves that Si acts as a donor and C acts as an acceptor in (1-101)GaN. We might conclude that the p-type conduction is due to the incorporation of C on the top surface of the N face of the GaN.

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3950/jibiinkoka.106.856

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

A GaN/AlGaN double heterostructure was fabricated on the (1101) facets of a GaN triangular structure prepared by selective area growth by metalorganic vapor phase epitaxy. The photoluminescence (PL) and cathode luminescence (CL) spectra were investigated to characterize the structure. It was found that the PL peak wavelength due to the GaN quantum well is dependent on the well thickness. However, the Al composition of the AlGaN layer is dependent on the position on the (1101) facet. The anomalous gradient of the composition is attributed to the difference in the diffusion coefficients of Al and Ga on the surface.

DOI： 10.1143/jjap.40.1896

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Selective area growth (SAG) of GaN on (111) Si substrate was studied using AlGaN as an intermediate layer. A hexagonal dot with a (0001) plane on the top and of a 5 µm or a submicron size was obtained using a patterned dot structure of silicon dioxide (SiO<SUB>2</SUB>) mask. The facet structure revealed that the <11\=20> axis of hexagonal GaN is parallel to the <110> axis of the Si substrate. The cathodoluminescence (CL) spectrum at 133 K exhibited a strong near-band-edge emission band for the submicron dots, which suggests excellent crystallinity. Epitaxial lateral overgrowth (ELO) of GaN on the Si substrate is demonstrated.

DOI： 10.1143/jjap.37.l966

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0tc01369b

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssa.201900955

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Herein, a newly developed birefringence microscope is used to observe dislocations in gallium nitride (GaN) substrates. The comparison results of the observation method using this microscope with other observation methods, such as X-ray topography and Raman microscopy, confirms that dislocations in a GaN substrate can be detected with a birefringence microscope. In addition, the observation can be carried out as easily as with an optical microscope. It is also found that under certain observation conditions, the direction of the edge component of dislocations can be determined.

DOI： 10.1002/pssb.201900553

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5145017

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1361-6641/ab63f1

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

The quantum efficiency (QE) of an InGaN photocathode as a function of InGaN layer thickness (240, 100, and 70 nm) was investigated. To activate the sample surface, Cs and O were deposited on the surface in an ultrahigh-vacuum chamber. The QE for different optical power densities was measured by irradiating excitation light from the front and back sides of each sample. The QEs for InGaN layer thickness of 240, 100, and 70 nm with back-side irradiation were 0.9, 9.8, and 7.5%, respectively. For the thicknesses of 70 and 100 nm, the QEs were higher for back-side irradiation than for front-side irradiation, whereas for the thickness of 240 nm, the QE was higher for front-side irradiation. The InGaN layer thickness dependence of the QEs for back- and front-side irradiations was calculated using a continuous equation considering processes such as excitation, diffusion, recombination, and escape of electrons from the surface of the photocathode. The tendency of the experimental results, where QE was maximum at 100-120 nm, corresponded to that of the calculated results.

DOI： 10.1016/j.mee.2020.111229

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The decomposition of trimethylgallium (Ga(CH3)(3)) was examined under H-2 and N-2 atmospheres using a high-resolution (about 0.002 u) time-of-flight mass spectrometry system, which enabled the separation of N-2 and ethene (C2H4) signals. Under H-2 atmosphere, the main decomposition product was methane (CH4) formed by the hydrogenolysis of Ga(CH3)(3). However, under N-2 atmosphere, the main product is ethane (C2H6) at temperature lower than 660 degrees C. Above 660 degrees C, the C2H6 further decomposes into CH4, acetylene (C2H2) and C2H4, and the main components in the gas phase are C2H2 and C2H4 above 1000 degrees C. Since these are effective carbon dopants, the molar ratio of H-2 to the Ga(CH3)(3) raw material in the carrier gas should be maintained above 300 to inhibit the formation of hydrocarbons in N-2. (C) 2020 The Japan Society of Applied Physics

DOI： 10.35848/1347-4065/ab6fb0

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We studied the nucleation and growth of hexagonal BN (h-BN) on AlN template on c-plane sapphire by metalorganic vapor phase epitaxy as functions of growth temperature, deposition time, and triethylboron (TEB) partial pressure. A lateral growth rate of about 25 nm min(-1) for h-BN nuclei was obtained by atomic force microscopy and a nucleation activation energy of 2.1 eV was extracted from the temperature dependence of the nucleation density. A large TEB flow rate strongly enhances the formation of h-BN nuclei. At a reduced TEB flow rate, we observed a significantly decreased nuclei density and a delay in nucleation due to TEB desorption. By fine tuning the growth parameters, single-crystalline multilayer h-BN was successfully formed on AlN surface, as confirmed by x-ray diffraction and transmission electron microscopy (TEM). The epitaxial relationship between h-BN and AlN was [0 0 0 1](h-BN) parallel to [0 0 0 1](AlN) and [1 0 -10](h-BN) parallel to [1 1 -20](AlN) from TEM and electron backscatter diffraction measurements. In addition, TEM showed that the initial h-BN layers are not parallel and tend to form half-domes. On those half-domes (cap-shaped-like) a 2D lateral growth sets on, resulting in a well-oriented 2D multilayer observed in TEM. Thus, the surface topography further develops to form a relatively flat surface without wrinkles and finally a typical hexagon-like wrinkled surface at thicker h-BN layers. Particularly, the small h-BN nuclei have dangling bonds at their periphery that can interact with the substrate, forming actual bonds with AlN. Hence the choice on the substrate is important, despite the basal planes of multilayer h-BN are bonded by a weak van der Waals force.

DOI： 10.1088/2053-1583/ab46e6

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1361-6641/ab4d2c

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/s19235107

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-019-52067-y

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

In this study, V-shaped dislocations in a GaN epitaxial layer on a free-standing GaN substrate were observed. Our investigation further revealed that the V-shaped dislocations were newly generated at the interface in the epilayer rather than propagated from the GaN substrate. V-shaped dislocations consist of two straight parts. The straight parts of the V-shaped dislocations were separated from each other in the m-direction and tilted toward the step-flow direction of the GaN epitaxial layer. The V-shaped dislocations are continuous single dislocations having a Burgers vector component of 1a and an intrinsic stacking fault between their straight parts.

DOI： 10.1063/1.5114866

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/ab2657

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The decomposition of ammonia (NH3) in nitrogen (N-2) ambient was studied under non-equilibrium conditions similar to those in a metal organic vapor phase epitaxy (MOVPE) reactor during the epitaxial growth of group-III nitrides. The gas phase was sampled at different positions and analyzed using a time-of-flight mass spectrometry system with a high resolution (better than 0.002 u). Our results expand earlier findings. Even at the high temperature of 1200 degrees C, only 26% of NH3 decomposed in a clean metal-free reactor, whereas a higher ratio of NH3 decomposition was realized in the presence of stainless steel. The activation energy in the clean reactor was calculated to be 0.965 +/- 0.004 eV. These results demonstrate the capability of our setup and shed new light on the elucidation of the vapor phase growth mechanism of group III-nitrides by MOVPE.

DOI： 10.1016/j.jcrysgro.2019.03.025

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/ab124e

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

DOI： 10.7567/1347-4065/ab1411

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/ab1252

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1882-0786/ab21a9

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2019.02.058

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Language：English   Publishing type：Research paper (scientific journal)  

This study examines the effect of (0 0 0 −1) GaN substrate misorientation on the residual impurities and surface morphology of N-polar GaN grown by metalorganic vapor-phase epitaxy. Carbon, silicon, and oxygen concentrations decreased with increasing GaN substrate misorientation angle, with the lowest impurity concentration achieved for a misorientation angle of 2° toward the m-axis, with 6 × 10 15 cm −3 carbon, 6 × 10 15 cm −3 silicon, and 4 × 10 17 cm −3 oxygen atoms. The oxygen concentration was measured at a depth of 0.5 μm below the wafer surface, and the oxygen concentration decreased with increasing thickness. The incorporation of carbon and oxygen revealed a strong dependence on the misorientation angle. The step distance height of the steps parallel to the [1 1 −2 0] direction (or perpendicular to the [1 −1 0 0] m-direction) was confirmed to be a double-height layer step. This phenomenon indicated that m-direction steps are stable for N-polar growth in GaN. In cases of large misorientation toward the m-axis in of the GaN substrate it was difficult to control the misorientation perpendicular to the nominal direction leading to a-axis direction by wafer bowing at wafer manufacturing. Therefore, step-bunching was generated for each symmetric m-axis due to an increase in the compound's off-angle, thus causing the surface roughness to become large.

DOI： 10.1016/j.jcrysgro.2019.02.013

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/1347-4065/aafe70

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Wafer trays with different gaps (the distance between the top of the pocket and the bottom of the wafer) were used to grow InGaN/GaN multiple quantum wells (MQWs) in a horizontal metalorganic vapor phase epitaxy (MOVPE) reactor. The numerical reactor simulation revealed that at the similar surface temperature the gas phase temperature around the wafer increases due to an increased wafer tray temperature. This increased gas phase temperature is expected to increase the effective V/III ratio by enhanced NH3 decomposition. Photoluminescence (PL) intensities of long-wavelength MQWs increased at the same indium content by the enhanced gas phase temperature, while the emission became narrow. This is related to a smoother topography at higher gas phase temperatures.

DOI： 10.1016/j.jcrysgro.2018.12.007

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/ma12050689

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PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2018.12.028

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2018.11.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A simple structure with high breakdown voltage and a low leakage current of a vertical GaN p-n diode on a GaN free-standing substrate is demonstrated. We describe a vertical p-n diode with a simple edge termination that has a drift layer etched deeply and vertically. A device simulation revealed that the electric field was more relaxed at the device edge and applied uniformly in the entire device with increasing etching depth. We fabricated the simulated structure and succeeded in reducing the leakage current and improving the breakdown voltage. With this structure, a stable avalanche breakdown can be observed. (C) 2019 The Japan Society of Applied Physics

DOI： 10.7567/1882-0786/aafdb9

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5063735

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Institute of Metals and Materials  

DOI： 10.2320/materia.58.103

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：A V S AMER INST PHYSICS  

A III-V semiconductor with a few monolayers of alkali metals (e.g., Cs) forms a negative electron affinity (NEA) surface, for which the vacuum level lies below the conduction band minimum of the base semiconductor. The photocathodes that form an NEA surface (NEA photocathodes) have various advantages, such as low emittance, a large current, high spin polarization, and ultrashort pulsed operation. The NEA-InGaN photocathode, which is sensitive to blue light, has been studied as a material for the next-generation robust photocathode. However, the proper conditions for forming NEA surfaces remain unknown. The authors consider whether the suitable process for NEA surfaces can be understood by investigating the relationship between the electron emission and the adsorption state of alkali metals. In this study, the relationship between the electron emission and the adsorption state of Cs on the p-type InGaN (0001) was analyzed by the temperature programed desorption (TPD) method using a quadrupole mass spectrometer. From the results of the TPD measurements, it was shown that there were several adsorption states of Cs on InGaN. The quantum efficiency (QE), which indicates the ratio of emitted electrons to incident photons, increased while Cs desorption occurred. The authors divided the formation process of an NEA surface into several sections to investigate the adsorption states of Cs related to the electron emission and to discuss the reasons why the QE increased despite the desorbed Cs. From the results of the NEA activation in each section, it was shown that there were sections where the QE increased by reacting with O-2 after Cs supply stopped. There is a possibility that several layers reacting with O-2 and those not reacting with O-2 are formed by performing NEA activation until the QE saturates. From the results of the TPD measurements in each section, it was suggested that there was a Cs peak at above 700 degrees C when the TPD method was carried out immediately after confirming the electron emission. Therefore, the adsorption state of Cs that formed a peak at above 700 degrees C had a close relation to the electron emission. It is considered that the increase of the QE in the TPD was affected by adsorbed Cs compounds that reacted with O-2. Although the mechanism is not understood, it is known that the QE was increased by the reaction of Cs adsorbed compounds and O-2 in previous studies. It was suspected that layers that reacted with O-2 appeared from TPD and then the QE increased by reacting with O-2. Published by the AVS.

DOI： 10.1116/1.5048061

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.57.105501

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2018.07.015

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.57.091001

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssr.201800124

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.57.070302

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

The main chain structure of optically isotropic amorphous fluorine resin for encapsulating AlGaN-based deep-ultraviolet LEDs (λ &lt
300 nm) is studied. One type of amorphous fluorine resin has a five-membered ring with a single oxygen atom and the other has that one with two oxygen atoms. Reliability testing is performed using AlGaN-based LEDs of 262 and 289 nm. For the resin with two oxygen atoms in the ring, visible damage to the electrode and significantly increased leakage current are considered to been caused by the photolysis of the ring induced by irradiation with deep-ultraviolet light. In contrast, electrode damage and increased leakage are not observed in the case of the resin with the single-oxygen ring.

DOI： 10.1002/pssa.201700525

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

In this study, GaN m-plane Schottky barrier diodes are fabricated by metalorganic vapor-phase epitaxy (MOVPE) on several off-angle gallium nitride (GaN) substrates, and the off-cut angle dependence of impurity incorporation is investigated. We show that the MOVPE layer on the substrate inclined 5° toward the [000–1] direction has extremely low impurity incorporation. These results provide important suggestions for the fabrication of m-plane power devices.

DOI： 10.1002/pssa.201700645

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/APEX.11.051002

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations is successfully grown on a silicon substrate by using in situ gas etching. Silicon nitride (SiNx) film is used as a mask, and ammonia is intermittently supplied in hydrogen ambient during the etching. After etching, high-density deep pits appeared on the surface of a GaN template layer and corresponded to the threading dislocations in the layer. In this novel method, before growing an additional GaN layer on the template GaN layer, a second SiNx layer is deposited after the etching process, and this layer prevents GaN nuclei from growing on the upper side-walls of the pits. By using this method, the density of threading dislocations of the GaN surface is reduced to 6.7x10(7)cm(-2). This method is cost effective, completing all the necessary processes in one growth run without taking samples out from a metalorganic chemical vapor deposition (MOCVD) reactor.

DOI： 10.1002/pssb.201700387

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicating that some types of dislocation cause reverse leakage. When etch pits were formed on the dislocations by KOH etching, three sizes of etch pits were obtained (large, medium, and small). Among these etch pits, only the medium pits coincided with leakage spots. Additionally, transmission electron microscopy observations revealed that pure screw dislocations are present under the leakage spots. The results revealed that lc pure screw dislocations are related to the reverse leakage in vertical p-n diodes. Published by AIP Publishing.

DOI： 10.1063/1.5024704

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH3) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH3 is supplied to fully convert the TEB within one cycle. Excess NH3 caused islands on h-BN film surface while a lack of NH3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c-plane sapphire was confirmed to be [0001](h-BN)||[0001](sapphire) and [10-10](h-BN)||[11-20](sapphire). It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2017.10.036

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1149/08612.0041ecst

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have developed a charge-to-time converting (QTC) leading-edge discriminator for plastic-scintillator signals, which is packaged in a NIM-standard double-width module. The pulse width of the discriminator output is approximately proportional to the charge integration of input signals up to 40-50 pC. The non-linearity is 20%, 10%, 4%, and 2% at maximum for the input charges below 7 pC, for 7-10 pC, for 10-20 pC, and above 20 pC, respectively, for the minimum input charges larger than 2 pC. The discriminator could be suitable in the measurement of the timing and charge of plastic-scintillator signals together with a multi-hit time-to-digital converter (TDC) module. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2017.09.040

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.

DOI： 10.1063/1.4994627

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We investigate the influence of crystal defects on p-type GaN grown by metalorganic vapor phase epitaxy. Sets of p-type GaN films were grown on sapphire substrates and on free-standing GaN (F-GaN) substrates simultaneously using various Et-Cp2Mg flow rates. Although there is a difference of two orders of magnitude between the threading dislocation densities of p-type GaN grown on sapphire and F-GaN substrates, there is no significant difference in hole concentration. However, there are problems with the surface morphology of p-type GaN grown on sapphire. The deterioration of the surface was caused by the difference in nanopipe density. The electrical properties of a p-n junction diode formed on sapphire with a high density of nanopipes were observed using emission microscopy under both forward- and reverse-bias conditions. Our results demonstrate that the nanopipes are electrically inactive, and that other types of threading dislocation have more influence on the current-voltage characteristics.

DOI： 10.1002/pssa.201600837

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

In this study, by using time-of-flight (TOF) high-resolution and high-sensitivity mass spectrometry measurements, the decomposition of trimethylgallium into dimethylgallium and monomethylgallium along with its adduct formation with NHx in a commercially available horizontal metalorganic vapor-phase epitaxy (MOVPE) reactor with a resistive heater was investigated and observed in more detail than previously reported. The results confirmed the use of the TOF monitoring system in analyzing the elementary reaction process in actual MOVPE systems. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.201600737

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The internal electric fields in III-polar (0001), N-polar (0001), and semipolar (1011) InGaN/GaN light-emitting diodes were investigated by electroreflectance (ER) spectroscopy. The ER spectra reflected the difference in the direction and strength of internal electric fields. Phase analyses of the ER signal revealed that only III-polar InGaN wells have the opposite direction of the internal electric field at zero bias voltage; this finding is in good agreement with the results of numerical analyses. Quantitative analyses of internal electric fields were conducted by the linewidth analyses of ER spectra. Our experimental results indicate that the absolute value of internal electric fields can be measured from ER spectra. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/APEX.10.082101

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

In this study, GaN m-plane Schottky barrier diodes fabricated with a metalorganic vapor-phase epitaxy on a GaN substrate were investigated using emission microscope, photoluminescence, and cathodoluminescence. In addition, facet dependence of leakage current under reverse-biased condition was observed. We showed that the leakage-current distribution was caused by the facet dependence of the carrier concentration and oxygen concentration. These results can provide important suggestions for the fabrication of m-plane devices. (a) four-faceted hillocks on m-plane GaN MOVPE sample, facet dependence of (b) leakage current and (c) PL peak intensity of the m-plane GaN Schottky barrier diode.

DOI： 10.1002/pssa.201600829

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Injecting current with a uniform carrier concentration is important for applications with three-dimensional architectures such as vertical power devices or displays. In III-nitride nanostructures, dopants not only incorporate differently depending on the surface orientation but can also seriously affect the kinetic equilibrium shapes of the nanorods. Herein, we report selective-area growth of doped GaN nanorods grown by pulsed-mode metalorganic chemical vapor deposition. Two dopants, Si and Mg, were employed as donor and acceptor atoms, respectively, for a mono-doping approach. Furthermore, a mixed flow of Si and Mg was supplied for a co-doping approach. We compared the morphological effects and growth rates of each doped GaN nanorod array. Then, we proposed appropriate growth mechanisms for the doped GaN nanorods on the basis of our structural characterizations. These results might extend the morphological functionality of GaN nanorods by including doping and may also provide an appropriate foundation for the design of nanostructure-based electronic or photonic devices. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.201600722

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7 +/- 0.5 nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices.

DOI： 10.1016/j.jcrysgro.2017.01.031

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have investigated the effect of V/III ratio on the surface morphology, impurity concentration and electrical properties of m-plane (10 (1) over bar0) Gallium Nitride (GaN) homoepitaxial layers. Four-sided pyramidal hillocks are observed on the nominally on-axis m-plane GaN films. Hillocks sizes relatively increase by increasing the V/III ratio. All facets of pyramidal hillocks exhibit well-defined step-terrace features. Secondary ion mass spectrometry depth profiles reveal that carbon impurities decrease by increasing the V/III ratio while the lowest oxygen content is found at an optimized V/III ratio of 900. Vertical Schottky barrier diodes fabricated on the m-GaN samples were characterized. Low leakage current densities of the order of 10(-10) A/cm(2) at -5 V are obtained at the optimum V/III ratio. Oxygen impurities and screw-component dislocations around hillocks are found to have more detrimental impact on the leakage current mechanism.

DOI： 10.1016/j.jcrysgro.2016.12.012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We successfully grew semipolar (10 (1) over bar3) and (10 (1) over bar5) GaN films on Si(001) substrates employing metal-organic chemical vapor deposition (MOCVD) by inserting a directionally sputtered AlN (DS-AlN) buffer layer. To improve the crystal quality of the orientation-controlled semipolar (10 (1) over bar3) and (10 (1) over bar5) GaN films, a two-step epitaxial lateral overgrowth (ELO) process was performed with a striped mask. According to low-temperature cathodoluminescence (LT-CL) characterization, the ELO results in a coalesced morphology and a low defect density of &lt; 2.72x10(8) cm(-2) for both semipolar (10&lt;(1)over bar&gt;3) and (10 (1) over bar5) GaN films. For comparing the properties of planar and ELO semipolar GaN, a rocking curve of x-ray diffraction (XRD) and low-temperature photoluminescence (LT-PL) spectra was measured. The crystal orientation of semipolar GaN films was confirmed using electron backscatter diffraction (EBSD).

DOI： 10.1016/j.jcrysgro.2016.11.116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Effect of rapid thermal annealing (RTA) on crystal defects in a GaN layer grown on a (111) Si substrate was investigated by photoluminescence (PL) and transmission electron microscopy (TEM) analyses. The PL spectra suggested that the density of gallium vacancy is not changed by the heat treatment up to 700 degrees C. In the TEM specimen, we had dislocation half loops generated by off-axis propagation of the threading dislocation. We found that the half-loop of c-type dislocation shrinks/moves by a repetitive RTA at 600-700 degrees C. In contrast, we could find no remarkable changes in the a-type or a+c-type dislocations.

DOI： 10.1016/j.jcrysgro.2017.01.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Severe melt-back etching has forced the epitaxy of GaN on Si to use an AlN buffer layer for growing high-quality two-dimensional layers, despite its high resistivity. Herein, we report a metal-based pre-orienting layer (POL) for growing GaN nanostructures (NSs) to replace the traditional AlN buffer layer. Two metals, titanium (Ti) and hafnium (Hf), were evaluated as POLs. We succeeded in fabricating arrays of GaN NSs with highly preferred orientation using selective-area growth. The crystallographic phase of the POLs critically affected the evolved orientation of the crystals. Photoluminescence measurements revealed that GaN NSs with Hf-based POLs were of reasonably high quality. We believe that this result will facilitate broader III-V semiconductor applications using alternative substrates moving beyond conventional Si-based optoelectronics.

DOI： 10.1016/j.jcrysgro.2016.10.032

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.56.061002

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/srep45345

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

High Al-composition AlGaN and AlN epilayers were grown directly on Si(111) substrate by a hydride vapor phase epitaxy (HVPE) method with a melted mixed source in a graphite boat set in a source zone with high temperatures of T = 700 and 800 degrees C, respectively. The presence of the Ga material in the mixed source of Ga and Al promoted the growth of AlN and AlGaN epilayers in the growth zone. When the temperature in the source zone was 800 degrees C, the crystalline quality of the AlN and AlGaN epilayers increased as the ratio of Ga to Al increased, and the optimum mix ratio of Ga to Al for the growth of AlN epilayers was approximately 0.35-0.42, obtained from a numerical fitting analysis of the X-ray diffraction (XRD) data for these epilayers. It appears that they can be grown directly by our melted-mixed-source HVPE method in a high-temperature source zone. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.56.01AD07

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We developed a vertical-type light-emitting diode (LED) in which the substrate is removed using a hydride vapor phase epitaxy (HVPE) apparatus consisting of a multi-graphite boat filled with a mixed source and a high-temperature (T approximate to 900 degrees C) RF heating coil outside the source zone. The new chip-growth process with a significant reduction in the number of production steps is completed in only four steps, namely, photolithography, epitaxial layer growth, sorting, and metallization. We analyze the emission mechanism of these lights from measurement results to validate the characteristics of the light emitted from these vertical-type blue LEDs and white LEDs (WLEDs) without substrates, and propose that this mixed-source HVPE method may be a promising production technique for LEDs. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.56.01AD03

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The planar epitaxial growth of semipolar (10 (1) over bar3) GaN on a Si(001) substrate was performed on a directionally sputtered AlN buffer layer. Three types of interlayers, i.e., single AlN, double AlN, and a stack of AlN/GaN layers were grown by metalorganic chemical vapor deposition (MOCVD) to achieve high quality GaN films. The results for the stack of AlN/GaN layers provide highest crystal quality and optical properties for GaN. Comparing the top (Ga face) and bottom (N face) surfaces of grown semipolar (10 (1) over bar3) GaN confirms the defect density reduction that is due to the application of interlayers. Moreover, reduced inversion domain density on the bottom surface is attributed with the insertion of interlayers. Improving the quality of semipolar GaN on Si(001) substrates is expected to be useful for GaN/Si(001) integrated optoelectronics. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2016.09.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H-2/N-2 carrier gas ratio, growth temperature, and absolute NH3/HCl gas flow resulted in changes in the growth morphology. In particular, for an optimized mixed-carrier gas ratio of H-2 to N-2, we achieved vertically well-aligned microrods. The topmost regions of the GaN microrods were terminated with pyramidal facets, indicating typical Ga polarity. The optical properties of the grown microrods were characterized by cathodoluminescence (CL) at a low temperature. This revealed that the GaN microrods had high crystal quality since they exhibited suppressed yellow luminescence as well as strong band edge emission. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2016.05.008

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

To replace mercury lamps with AlGaN-based deep-ultraviolet (DUV) LEDs, a simple and low-cost package with increased light extraction efficiency (LEE) is indispensable. Therefore, resin encapsulation is considered to be a key technology. However, the photochemical reactions induced by DUV light cause serious problems, and conventional resins cannot be used. In the former part of this study, a comparison of a silicone resin and fluorine polymers was carried out in terms of their suitability for encapsulation, and we concluded that only one of the fluorine polymers can be used for encapsulation. In the latter part, the endurance of encapsulation using the selected fluorine polymer was investigated, and we confirmed that the selected fluorine polymer can guarantee a lifetime of over 6,000 h at a wavelength of 265nm. Furthermore, a 3 x 4 array module of encapsulated dies on a simple AlN submount was fabricated, demonstrating the possibility of W/cm(2)-class lighting. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.082101

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Using an in situ laser absorption and scattering method, the surface roughness and incorporation of In in InGaN layers grown by metal organic vapor-phase epitaxy (MOVPE) were monitored. We observed that the laser light with energy higher than the GaN bandgap was fully absorbed in a GaN layer with a smooth film surface. On the other hand, we observed that the scattering laser light from the surface when the roughness of the InGaN surface increased owing to the formation of In droplets. Laser light with energy lower than the GaN bandgap was weakly absorbed by the GaN layer and was scattered at the back surface of the wafer. Furthermore, laser light intensity decreased during InGaN growth because of In incorporation. The threshold of trimethyl-In (TMIn) for the formation of In droplets as a function of growth temperature was determined using our in situ system. Moreover, we observed that the In droplets were removed by thermal or H-2 treatment. The results indicate that multiwavelength laser absorption and scattering enable the optimization of the growth conditions for In-rich InGaN. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FD03

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Previously, we reported a growth method for GaN on SiC by metalorganic vapor phase epitaxy. By using a preflow trimethylaluminum treatment, the poor wetting problem of gallium on the SiC surface was alleviated, resulting in a 1.2-mu m-thick crack-free GaN grown on an on-axis 6H-SiC(0001) substrate via an ultrathin AlGaN interlayer. In this study, the impact of the preflow trimethylaluminum treatment time is investigated to understand why a crack-free epilayer was realized. To demonstrate the electrical performance of devices formed by our technique, GaN/SiC vertical Schottky barrier diodes were fabricated and compared with GaN/AlN/SiC and GaN/GaN vertical Schottky barrier diodes. Compared with diodes including a high-resistance AlN interlayer, the series resistance of GaN/SiC Schottky barrier diodes incorporating the ultrathin interlayer with 5 s of TMAl treatment showed a marked reduction from 4.0 x 10(7) to 2.0 x 10(-1) Omega.cm(2). The ultrathin interlayer growth technique is expected to be applied in future GaN/SiC hybrid high-power and high-frequency devices. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FB06

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A thin p-type InGaN with a negative electron affinity (NEA) surface was used to measure the relaxation time of a surface charge limit (SCL) by irradiating rectangular laser beam pulses at changing time interval. The p-type InGaN film was grown by metal organic vapor phase epitaxy and the NEA activation was performed after the sample was heat cleaned. 13 nC per pulse with 10ms width was obtained from the InGaN photocathode. The current decreased exponentially from the beginning of the pulse. The initial current value after the laser irradiation decreased with the time interval. As a result, the SCL relaxation time was estimated through the InGaN photocathode measurements at 100 ms. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FH05

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Low-toxity high-In-content InGaN is an attractive option for short-distance communications through plastic optical fibers because its performance is only slightly affected by temperature. However, its fabrication on the c-plane is impaired by In droplets and V pits, which form at low-growth temperature. On the other hand, unlike the c-plane, (1 (1) over bar 01) InGaN relaxes with tilting. Therefore, in this study, we first grew a high-In-content InGaN single layer, and then we fabricated an InGaN tilting layer between (1 (1) over bar 01) InGaN-based multiple quantum wells (MQWs) and GaN stripes/(001) Si. The emission wavelength increased with the InGaN tilting layer's growth time because the strain was relaxed by misfit dislocations at the heterointerface. This layer also extended the emission peak of InGaN/GaN MQWs and increased the photoluminescence intensity with respect to that of a single-layered InGaN. Therefore, the InGaN tilting layer is effective for growing high-In-content (1 (1) over bar 01) InGaN MQWs. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FA10

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Even though a patterned sapphire substrate (PSS) has been used for the growth of a high-quality epilayer because of its many advantages, it has not been successfully used to grow an AlN epilayer for ultraviolet (UV) light-emitting diodes (LEDs) on a PSS up to now. We report the growth of a high-quality AlN epilayer on a PSS, as a substrate for the manufacture of UV LEDs, by hydride vapor phase epitaxy (HVPE). The X-ray diffraction (XRD) peaks for the AlN epilayer grown on the PSS indicate that crystalline AlN with a wurtzite structure was grown successfully on the PSS. Furthermore, HVPE combining both in situ HVPE technology and liquid-phase epitaxy (LPE) using a mixed source is proposed as a novel method for the growth of a flat AlN epilayer on a PSS. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FC02

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In this paper, we discuss the influence of parameters such as type of carrier gas and NH3/HCl flow ratio on the growth of vertical GaN microstructures by selective-area growth (SAG) hydride vapor phase epitaxy (HVPE). On various strain-induced templates such as GaN/sapphire, GaN/Si, and AlN/Si, regular arrays of Ga-polar GaN microrods were properly achieved by adjusting the growth parameters. The photoluminescence and micro-Raman measurements reveal not only the crystal quality of the GaN microrods but also strain distribution. These results will give insight into the control of the morphology of GaN microrods in terms of the strain induced from templates in SAG-HVPE. The precisely controlled arrays of GaN microrods can be used for next-generation light-emitting diodes (LEDs) by realizing InGaN/GaN multi-quantum wells (MQWs) with a radial structure. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FF03

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigated the surface reconstruction of InN(0001) during raised-pressure metalorganic vapor-phase epitaxy using an ab initio-based approach. We observed that the reconstructed structure changes from In-rich surfaces such as In bilayer and monolayer surfaces to an ideal surface with increasing growth temperature. In addition, we investigated the effects of surface reconstruction on the growth process using a newly improved thermodynamic analysis method. Although no barrier is present in the growth reaction when the In-rich surfaces appear, the results suggest that the surface phase acts as a barrier in the growth reaction when the ideal surface appears. Furthermore, we discuss the growth conditions that enable high-temperature growth with a smooth reaction path. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FM01

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Recently, GaN, which has remarkable properties as a material for optical devices and high-power electron devices, has also attracted attention as a material for radiation detectors. We previously suggested the use of BGaN as a neutron detector material. However, the radiation detection characteristics of GaN itself are not yet adequately understood. For realizing a BGaN neutron detector, the understanding of the radiation detection characteristics of GaN, which is a base material of the neutron detector, is important. In this study, we evaluated the radiation detection characteristics of GaN. We performed I-V and energy spectrum measurements under alpha ray, gamma ray, and thermal neutron irradiations to characterize the radiation detection characteristics of a GaN diode. The obtained results indicate that GaN is an effective material for our proposed new BGaN-based neutron detector. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FJ02

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the material and optical properties of core-shell InGaN layers grown on GaN nanorod arrays. The core-shell InGaN layers were well grown on polarization-reduced surfaces such as semipolar pyramids and nonpolar sidewalls. In addition, to compensate the biaxial strain between GaN and InGaN layers, we grew interlayers underneath a thick InGaN layer. Here, the interlayers were composed of multiple superlattice structures. We could observe that the indium composition of core-shell InGaN structures increased with the number of interlayers. This indicates that the absorption energy band of InGaN alloys can be better matched to the spectral irradiance of the solar spectrum in nature. We also implemented a simulation of Ga-polar and nonpolar InGaN-based solar cells based on the indium composition obtained from the experiments. The result showed that nonpolar InGaN solar cells had a much higher efficiency than Ga-polar InGaN solar cells with the same thickness of the absorption layer. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.05FG03

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We report the selective-area growth of a gallium nitride (GaN)-nanorod-based InGaN/GaN multiple-quantum-well (MQW) core-shell structure embedded in a three-dimensional (3D) light-emitting diode (LED) grown by metalorganic chemical vapor deposition (MOCVD) and its optical analysis. High-resolution transmission electron microscopy (HR-TEM) observation revealed the high quality of the GaN nanorods and the position dependence of the structural properties of the InGaN/GaN MQWs on multiple facets. The excitation and temperature dependences of photoluminescence (PL) revealed the m-plane emission behaviors of the InGaN/GaN core-shell nanorods. The electroluminescence (EL) of the InGaN/GaN core-shell-nanorod-embedded 3D LED changed color from green to blue with increasing injection current. This phenomenon was mainly due to the energy gradient and deep localization of the indium in the selectively grown InGaN/GaN core-shell MQWs on the 3D architecture.

DOI： 10.1186/s11671-016-1441-6

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Using a SiNx insertion layer to reduce dislocations, enhanced photovoltaic properties could be obtained in p-i-n InGaN/GaN heterojunction solar cell. To investigate the influence of the dislocations on the photovoltaic behaviors, a sample grown without SiNx insertion layer was identically prepared for comparison. From optical properties measurements, the reduction in the number of non-radiative centers and a stronger In localization effect was shown in the sample with SiNx insertion layer. However, the quantum confined stark effect was almost negligible in both the samples. Electrical properties measurement showed reduced saturation current and increased shunt resistance in the sample with SiNx insertion layer due to the reduced dislocation density. By comparing these results and using a numerical model, the influence of the dislocation density on the different photovoltaic properties such as open-circuit voltage and fill factor has been confirmed. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.030306

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

To understand the effect of piezoelectric fields on carrier dynamics, we numerically investigated a simple p-GaN/i-InxGa1-xN/n-GaN solar cell structure. A reliable simulation model was obtained by comparing the experimental and simulated results in advance. The same p-i-n InGaN structures were re-simulated with and without the piezoelectric field effect, as spontaneous polarization remained unchanged. The sample with the piezoelectric field effect showed higher short current density (J(sc)), a staircase-like feature in its I-V curve, and higher open circuit voltage (V-oc) with a lower fill factor (F.F.) and reduced conversion efficiency (C.E.) than the sample with no piezoelectric fields. In addition, with increasing In fraction (x), the V-oc value gradually increased while the J(sc) value significantly decreased, correspondingly leading to a reduction in C.E. and F.F. values of the structure with the piezoelectric field effect. To solve the current loss problem, we applied various piezoelectric field elimination techniques to the simulated structures.

DOI： 10.1088/0022-3727/49/2/025103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Previously, we reported a growth method by metalorganic vapor phase epitaxy using a single two- dimensional growth step, resulting in 1.2-mu m crack-free GaN directly grown on 6H-SiC substrate. The introduction of Al-treatment prior to the standard GaN growth step resulted in improved surface wetting of gallium on the SiC substrate. Transmission electron microscope and energy dispersive spectrometer analysis of the epitaxial interface to the SiC determined that an ultra-thin AlGaN interlayer had formed measuring around 2-3 nm. We expect our growth technique can be applied to the fabrication of GaN/SiC high frequency and high power devices. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.010303

Web of Science

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

AlGaN-based LEDs are expected to be useful for sterilization, deodorization, photochemical applications such as UV curing and UV printing, medical applications such as phototherapy, and sensing. Today, it has become clear that efficient AlGaN-based LED dies are producible between 355 and 250 nm with an external quantum efficiency (EQE) of 3% on flat sapphire. These dies were realized on flat sapphire without using a special technique, i.e., reduction in threading dislocation density or light extraction enhancement techniques such as the use of a photonic crystal or a patterned sapphire substrate. Despite the limited light extraction efficiency of about 8% owing to light absorption at a thick p-GaN contact layer, high EQEs of approximately 6% has been reproducible between 300 and 280 nm without using special techniques. Moreover, an EQE of 3.9% has been shown at 271 nm, despite the smaller current injection efficiency (CIE). The high EQEs are thought to correspond to the high internal quantum efficiency (IQE), indicating a small room for improving IQE. Accordingly, resin encapsulation on a simple submount is strongly desired. Recently, we have succeeded in demonstrating fluorine resin encapsulation on a ceramic sheet (chip-on-board, COB) that is mass-producible. Furthermore, the molecular structure of a resin with a durability of more than 10,000 h is explained in this paper from the photochemical viewpoint. Thus, the key technologies of AlGaN-based DUV-LEDs having an EQE of 10% within a reasonable production cost have been established. The achieved efficiency makes AlGaN-based DUV-LEDs comparable to high-pressure mercury lamps.

DOI： 10.1117/12.2235398

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

To extend the availability of nanostructure-based optoelectronic applications, vertically elongated nanorods with precisely controlled morphology are required. For group III nitrides, pulsed-mode growth has recently been reported as an effective method for growing nanorod arrays with geometric precision. Here, we demonstrated the growth of arrays of highly elongated nanorods on Si substrates by metal-organic chemical vapor deposition using a pulsed-mode approach. Unlike the thick and high (or middle)-quality GaN templates normally used, nanorod growth was performed on an ultrathin and low-quality AlN/Si platform. Using kinetically controlled growth conditions and a patterning process, exceptionally long GaN nanorods were achieved with high geometric precision. The grown nanorods showed considerably improved optical and structural properties while remaining in uniform arrays. This approach can be used with a variety of materials to obtain nanorods with high quality, high uniformity, and high aspect ratio, and it can also serve as an effective fabrication method for InAlGaN-alloyed core/shell nanostructures for optoelectronic nano-devices with ultrahigh efficiency.

DOI： 10.1039/c5ce02056e

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The optical properties of InGaN/GaN multiple quantum wells (MQWs) have been studied by means of photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. The radiative and nonradiative recombination lifetimes were evaluated as a function of the excitation energy density. The radiative recombination lifetime decreased and subsequently reached a nearly constant value with increasing excitation energy density, which was attributed to screening of internal electric fields by photoexcited carriers. On the other hand, the nonradiative recombination lifetime increased and subsequently decreased with increasing excitation energy density. The initial increase in the nonradiative recombination lifetime could be attributed to saturation of nonradiative recombination centers with photoexcited carriers. The nonradiative recombination lifetime was found to decrease to a considerably weaker extent than that expected for the Auger recombination process of free carriers. This indicated that the decrease in the internal quantum efficiency (IQE) at high carrier densities could not be explained only by the Auger recombination process of free carriers. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.201451491

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We demonstrated lasing action and investigated the optical properties of (1 (1) over bar 01) multiquantum-well (MQW) stripe crystals on patterned (001) Si substrates. Longitudinal and higher order transverse modes were observed from a ridge waveguide structure. These results strongly suggest the possibility of fabricating (1 (1) over bar 01) InGaN MQW laser diodes on (001) Si. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/APEX.8.022702

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Highly ordered, position-controlled gallium nitride (GaN) nanowire based multiple-quantum-wells (MQWs) core-shell architecture arrays are synthesized by metalorganic chemical vapor deposition (MOCVD). We investigate the possibility of using GaN nanowire arrays as a basal template for the growth of InxGa1-xN/GaN MQWs. The MQWs on three different crystal facets (c(-), m(-), and semipolar-plane) of GaN nanowire exhibit dissimilar structural properties. The structural characteristics of InGaN/GaN core-shell arrays are inspected by cross-sectional high-resolution transmission electron microscopy (HR-TEM). We also investigate the optical properties of MQW core-shell structure nanoarrays. The luminescent characteristics of InGaN/GaN core-shell structure arrays are determined by photoluminescence (PL) and cathodoluminescence (CL) measurements. The monochromatic CL images clearly show the light emission behavior of InGaN/GaN MQW coaxial structure. Two distinguishable light emission peaks were observed in the GaN nanowire based core-shell structure. The characteristic of light emission mainly depends on the properties of MQWs, which are generated from different crystal facets of GaN. In addition, the light emission intensity shows different behaviors depending on the area of the GaN nanowire m-plane. The results of this study suggest that GaN nanowire arrays can be used as a good alternative basal template for next-generation light-emitting diodes (LEDs). (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.nanoen.2014.11.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

High-optical-quality GaN was grown on a (111) Si substrate by metal-organic vapor phase epitaxy using an AlInN buffer layer and an indium doped AlN nucleation layer. The photoluminescence spectra at room temperature showed a strong and narrow edge-emission peak and weak defect-related emission bands. We found four spectral peaks in the green and yellow luminescence bands at G(0): 514.5 nm (2.410 eV), G(1): 546.5nm (2.269 eV), Y-1: 553.5nm (2.240 eV), and Y-0: 584.5nm (2.121 eV), independent of the growth methods/conditions. The results suggest that the emission is associated with an intrinsic defect such as a Ga vacancy. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.11RC02

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

The photocathode using Negative Electron Affinity (NBA) surface on a semiconductor has been applied for science technologies such as an elemental particle experiment as an electron beam source. Yet, since NBA-surface is fragile, it is necessary to figure out how to make its life time longer in order to develop new technologies. Then, we realized that considering the band gap in semiconductor, the life time becomes longer as the negative affinity goes even smaller. Therefore, we produced the photocathodes using GaN and InGaN that have wider band gaps than that of GaAs. As a result, using GaN and InGaN, we gained 17 times and 7 times longer life time NEA-surface than that of GaAs, respectively. On the other hand, the result indicates that we can produce the NEA-surface with only cesium.

CiNii Books

Language：English   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

We realized p-GaN by high temperature Mg ion implantation with pre-sputter(PS) technique. Due to the new PS technique and high temperature implantation, ion implantation damage was greatly reduced. This soft implantation made the post anneal more effectively to recover the implantation damage and activate the implanted Mg ions. We believe this p-GaN by Mg ion implantation will contribute to GaN to enter high output power device application field.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We realized p-GaN by high temperature Mg ion implantation with pre-sputter(PS) technique. Due to the new PS technique and high temperature implantation, ion implantation damage was greatly reduced. This soft implantation made the post anneal more effectively to recover the implantation damage and activate the implanted Mg ions. We believe this p-GaN by Mg ion implantation will contribute to GaN to enter high output power device application field.

CiNii Books

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We realized p-GaN by high temperature Mg ion implantation with pre-sputter(PS) technique. Due to the new PS technique and high temperature implantation, ion implantation damage was greatly reduced. This soft implantation made the post anneal more effectively to recover the implantation damage and activate the implanted Mg ions. We believe this p-GaN by Mg ion implantation will contribute to GaN to enter high output power device application field.

CiNii Books

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The characteristics of nonpolar a-plane (11 (2) over bar0) GaN (a-GaN) grown using single and double nanopillar SiO2 masks were investigated. The two nanopillar SiO2 masks were directly fabricated on an r-plane sapphire substrate and a-GaN by the epitaxial lateral overgrowth (ELOG) technique. Through the use of the single and double nanopillar SiO2 masks, the crystalline quality and optical properties of a-GaN were markedly improved because of the nanoscale ELOG effect and a number of voids in the single and double nanopillar SiO2 mask areas in comparison with the planar sample. The submicron pit densities of the planar, single, and double nanopillar mask samples were similar to 2 x 10(9), similar to 7 x 10(8), and similar to 4 x 10(8) cm(-2), respectively. The internal quantum efficiency (IQE) values at room temperature of three-period InGaN/GaN multiple quantum wells (MQWs) grown using the planar, single, and double nanopillar masks were 45, 60, and 68% at a carrier concentration of 1.0 x 10(18) cm(-3), respectively. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.05FL01

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The effects of GaN quantum barriers with changing growth temperatures on the interfacial characteristics of GaN/InGaN single quantum well (SQW) grown on GaN templates by metalorganic vapour phase epitaxy were in situ investigated by X-ray crystal truncation rod (CTR) scattering and X-ray reflectivity measurements at growth temperature using a laboratory level X-ray diffractometer. Comparing the curve-fitting results of X-ray CTR scattering spectra obtained at growth temperature with that at room temperature, the InxGa1-xN with indium composition less than 0.11 was stabile of the indium distribution at the interface during the whole growth processes. By using several monolayers thickness GaN capping layer to protect the InGaN well layer within temperature-ramping process, the interfacial structure of the GaN/InGaN SQW was drastically improved on the basis of the curve-fitting results of X-ray CTR scattering spectra, and the narrow full width at half-maximum and strong luminous intensity were observed in room temperature photoluminescence spectra. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4867640

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Regularly distributed nanopyramid arrays with a highly uniform size were grown by selective-area growth. The nanopyramid size could be tuned by varying the growth time. Two emission peaks were observed from multiple quantum wells grown on the nanopyramids. The longer-wavelength peak originated from the apexes of pyramids with threefold symmetry. High-density stacking faults observed at these triangular apexes might be responsible for the higher indium incorporation. The formation of embedded voids inside the pyramids was explained by the different growth rates at the edge and center of the mask window caused by the low diffusion length. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.030306

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A novel activation process for Mg-implanted GaN was demonstrated. As opposed to the conventional thermal annealing process, an H-2/NH3 alternating supply annealing process achieved better optical activation, stronger near-ullraviolel luminescence and weaker yellow luminescence in the phololuminescence spectroscopy. After this process, small hexagonal hillocks were observed on the surface, which indicated that crystal regrowth was induced by this process, consisting of decomposition of GaN by H-2 supplies and re-crystallization by NH3 supplies. It was revealed that the implanted Mg could easily be located at the activation site by means of crystal regrowth by this process. (C) 2013 Elsevier B.V. All rights reserved

DOI： 10.1016/j.jcrysgro.2013.07.011

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Nonpolar a-plane (11-20) GaN (a-GaN) layers with low overall defect density and high crystalline quality were grown on r-plane sapphire substrates using etched a-GaN. The a-GaN layer was etched by pulse NH3 interrupted etching. Subsequently, a 2-mu m-thick Si-doped a-GaN layer was regrown on the etched a-GaN layer. A fully coalescent n-type a-GaN layer with a low threading dislocation density (similar to 7.5 x 10(8) cm(-2)) and a low basal stacking fault density (similar to 1.8 x 10(5) cm(-1)) was obtained. Compared with a planar sample, the full width at half maximum of the (11-20) X-ray rocking curve was significantly decreased to 518 arcsec along the c-axis direction and 562 arcsec along the m-axis direction. (C) 2014 Optical Society of America

DOI： 10.1364/OE.22.003585

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PubMed

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DOI： 10.1002/pssc.201300437

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

A GaN layer of 20 mu m thickness grown by the liquid-phase epitaxy on c-plane sapphire was used as a template for the growth of blue light-emitting diodes (LEDs) with emission peak wavelengths of about 450 nm. As the underlying layer of the active region, an InGaN/GaN superlattice or two pairs of 100 nm undoped GaN and 20 nm GaN: Si layers on an n-type GaN: Si layer was found to be effective for reducing the forward voltage. By optimizing the multiple-quantumwell structure, LEDs having a 2.5-nm-thick InGaN well and 5-nm-thick GaN barrier exhibited the highest internal quantum efficiency (IQE) at both low and high currents. This IQE was much higher than that of LEDs on a sapphire substrate. The IQE of LEDs using the liquid-phase GaN grown on sapphire substrate exceeded more than 75% at a forward current density of over 200 A/cm(2).

DOI： 10.1117/12.2038764

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

In this paper, we demonstrate a scalable process for the precise position-controlled selective growth of GaN nanowire arrays by metalorganic chemical vapor deposition (MOCVD) using a pulsed-mode growth technique. The location, orientation, length, and diameter of each GaN nanowire are controlled via pulsed-mode growth parameters such as growth temperature and precursor injection and interruption durations. The diameter and length of each GaN nanowire are in the ranges of more than 240 nm and 250-1250 nm, respectively, with different vertical-to-lateral aspect ratios that depend on the growth temperature. Also, it is found that a higher growth temperature helps increase the vertical growth rate and reduces the lateral growth rate of GaN nanowire arrays. Furthermore, in the case of longer TMGa injection duration, the Ga-rich region allows the higher lateral growth rate of GaN nanostructures, which leads to a transition in the morphology from nanowires to a thin film, while in the case of longer NH3 injection duration, the surface morphology changes from nanowires to pyramidal structures. In addition, the surface structure can also be controlled by varying the precursor interruption duration. Finally, we report and discuss a growth model for GaN nanowire arrays under pulsed-mode MOCVD growth.

DOI： 10.1039/c3ce42266f

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1002/pssc.201300470

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1002/pssc.201300670

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

MOVPE法を用いてGaN及びAlGaNへのMgとCの同時ドーピングを行い、電気的、光学的特性を評価した。GaNへの同時ドーピングでは比較的低濃度のCドーピングにより正孔密度の増加が確認できたが、AlGaNにおいてはC_2H_2流量増加に伴い正孔密度は減少した。cathodeluminescence(CL)測定により、全ての試料で440nm付近の発光を確認した。GaNへのMgとCのδドーピングを行った試料に対して同様の測定を行った。MgとCの同時δドーピングは通常のMgドーピングよりも高い正孔密度を示した。

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

MOVPE法を用いてGaN及びAlGaNへのMgとCの同時ドーピングを行い、電気的、光学的特性を評価した。GaNへの同時ドーピングでは比較的低濃度のCドーピングにより正孔密度の増加が確認できたが、AlGaNにおいてはC_2H_2流量増加に伴い正孔密度は減少した。cathodeluminescence(CL)測定により、全ての試料で440nm付近の発光を確認した。GaNへのMgとCのδドーピングを行った試料に対して同様の測定を行った。MgとCの同時δドーピングは通常のMgドーピングよりも高い正孔密度を示した。

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

MOVPE法を用いてGaN及びAlGaNへのMgとCの同時ドーピングを行い、電気的、光学的特性を評価した。GaNへの同時ドーピングでは比較的低濃度のCドーピングにより正孔密度の増加が確認できたが、AlGaNにおいてはC_2H_2流量増加に伴い正孔密度は減少した。cathodeluminescence(CL)測定により、全ての試料で440nm付近の発光を確認した。GaNへのMgとCのδドーピングを行った試料に対して同様の測定を行った。MgとCの同時δドーピングは通常のMgドーピングよりも高い正孔密度を示した。

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

我々は、負の電子親和力を持つ半導体表面を用いた電子源(NEA半導体フォトカソード電子源)の高輝度、高耐久化を目指して、p-GaN半導体を用いた機能性表面の寿命に対する電子源の高輝度条件を検討した。超高真空中でp-GaN基板に対してNEA表面活性化を行った後、その量子効率の波長依存性及びその寿命の測定実験を行った。その結果から、p-GaN基板は、従来技術のp-GaAs基板に比べて20倍以上寿命が長く、より高耐久性能を持つことが分かった。また、表面機能が低下するに連れて、バンドギャップエネルギー以下の励起エネルギーでの量子効率が優先的に減少することが分かった。これらの結果より、p-GaN基板を用いたNEA半導体フォトカソード電子源は、高耐久である一方で、表面機能が劣化した状態がより電子ビーム源として単色化に適していることを明らかにした。

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

我々は、負の電子親和力を持つ半導体表面を用いた電子源(NEA半導体フォトカソード電子源)の高輝度、高耐久化を目指して、p-GaN半導体を用いた機能性表面の寿命に対する電子源の高輝度条件を検討した。超高真空中でp-GaN基板に対してNEA表面活性化を行った後、その量子効率の波長依存性及びその寿命の測定実験を行った。その結果から、p-GaN基板は、従来技術のp-GaAs基板に比べて20倍以上寿命が長く、より高耐久性能を持つことが分かった。また、表面機能が低下するに連れて、バンドギャップエネルギー以下の励起エネルギーでの量子効率が優先的に減少することが分かった。これらの結果より、p-GaN基板を用いたNEA半導体フォトカソード電子源は、高耐久である一方で、表面機能が劣化した状態がより電子ビーム源として単色化に適していることを明らかにした。

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人電子情報通信学会  

我々は、負の電子親和力を持つ半導体表面を用いた電子源(NEA半導体フォトカソード電子源)の高輝度、高耐久化を目指して、p-GaN半導体を用いた機能性表面の寿命に対する電子源の高輝度条件を検討した。超高真空中でp-GaN基板に対してNEA表面活性化を行った後、その量子効率の波長依存性及びその寿命の測定実験を行った。その結果から、p-GaN基板は、従来技術のp-GaAs基板に比べて20倍以上寿命が長く、より高耐久性能を持つことが分かった。また、表面機能が低下するに連れて、バンドギャップエネルギー以下の励起エネルギーでの量子効率が優先的に減少することが分かった。これらの結果より、p-GaN基板を用いたNEA半導体フォトカソード電子源は、高耐久である一方で、表面機能が劣化した状態がより電子ビーム源として単色化に適していることを明らかにした。

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssc.201200587

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We grew high-quality semipolar (1-101) GaN stripes on a Si substrate by selective area growth and regrew InGaN/GaN MQW on these stripes with MOVPE. The PL peak wavelength at 300 K and InGaN well thickness for the obtained samples were 435-590 nm and 2-9 nm, respectively. In PL measurements from the surface, we found that a shorter wavelength and thinner well sample have PL polarization perpendicular to the c axis. On the other hand, as the PL wavelength is longer and/or the well is thicker, the PL polarization shifts from perpendicular to parallel. In the PL measurement from the (11 -22) edge surface of the sample with shorter wavelength, we observed the narrowing of PL spectrum. In addition, the parallel component of PL polarization increased with increase in well thickness. Therefore, we can control the direction of polarization by managing well thickness and indium composition and apply to make a LD structure.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We grew high-quality semipolar (1-101) GaN stripes on a Si substrate by selective area growth and regrew InGaN/GaN MQW on these stripes with MOVPE. The PL peak wavelength at 300 K and InGaN well thickness for the obtained samples were 435-590 nm and 2-9 nm, respectively. In PL measurements from the surface, we found that a shorter wavelength and thinner well sample have PL polarization perpendicular to the c axis. On the other hand, as the PL wavelength is longer and/or the well is thicker, the PL polarization shifts from perpendicular to parallel. In the PL measurement from the (11 -22) edge surface of the sample with shorter wavelength, we observed the narrowing of PL spectrum. In addition, the parallel component of PL polarization increased with increase in well thickness. Therefore, we can control the direction of polarization by managing well thickness and indium composition and apply to make a LD structure.

Language：English   Publishing type：Research paper (scientific journal)