Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Formation mechanism of threading-dislocation array in AlN layers grown on 6H-SiC (0001) substrates with 3-bilayer-high surface steps

Okumura Hironori, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS LETTERS Vol. 105 ( 7 ) 2014.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

We grew AlN layers on 6H-SiC (0001) substrates with three Si-C bilayer high (0.75nm) steps. In the AlN layers, most of the threading dislocations (TDs) were arranged in rows. The TD row consisted of arrays of a half-loop dislocation, which was formed by an AlN/SiC interfacial dislocation along the step edges of the SiC substrate surfaces and a TD pair at both ends. The configuration of the interfacial dislocation was highly relevant with two-dimensional AlN nuclei at the initial stage of growth. We concluded that the half-loop dislocation arrays were generated in the AlN nucleus coalescence over the SiC step edges. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4892807

Enhancement of carrier lifetime in lightly Al-doped p-type 4H-SiC epitaxial layers by combination of thermal oxidation and hydrogen annealing

Okuda Takafumi, Miyazawa Tetsuya, Tsuchida Hidekazu, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 7 ( 8 ) 2014.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

We investigated the enhancement of carrier lifetime in lightly Al-doped p-type 4H-SiC epilayers (NA ≃ 2 × 1014cm-3) by postgrowth processing. A carrier lifetime of 2.8 ìs in an as-grown epilayer is increased to 5.1 μs by carbon vacancy elimination, i.e., thermal oxidation at 1400 °C for 48 h. It reaches 10 μs by subsequent hydrogen annealing at 1000 °C for 10 min. The carrier lifetime in the as-grown epilayer is also increased to 4.0 μs by only hydrogen annealing. These results suggest that, in addition to carbon vacancy, there is another lifetime killer in p-type SiC, which cannot be eliminated by thermal oxidation but can be passivated by hydrogen annealing. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.7.085501

Conduction-type dependence of thermal oxidation rate on SiC(0001)

Kobayashi T., Suda J., Kimoto T.

IMFEDK 2014 - 2014 International Meeting for Future of Electron Devices, Kansai 2014.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IMFEDK 2014 - 2014 International Meeting for Future of Electron Devices, Kansai

The conduction-type dependent thermal oxidation rate in SiC was discovered. The oxidation was performed for SiC(0001) with nitrogen doping (n-type) in the range from 2.0×1016cm-3to 1.0×1019cm-3, and aluminum doping (p-type) in the range from 2.0×1015cm-3to 1.0×1019cm-3, exhibiting a clear dependence. For n-type SiC the oxide thickness increases for higher doping density, and for p-type the thickness decreases. Note that in the case of Si oxidation, there exists very little difference of oxidation rate between the conduction types in such low doping density, and the dependence is peculiar to SiC. The authors speculate the difference originates from the difference in carrier (electron/hole) density during the oxidation, which can reasonably explain the difference in the oxidation rate between Si and SiC.

DOI： 10.1109/IMFEDK.2014.6867060

Phonon-Limited Electron Mobility in Rectangular Cross-Sectional Ge Nanowires

Tanaka Hajime, Mori Seigo, Morioka Naoya, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 61 ( 6 ) page： 1993 - 1998 2014.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

The phonon-limited electron mobility in rectangular cross-sectional germanium (Ge) nanowires (NWs) with various orientations was theoretically investigated. The electronic states were calculated by a tight-binding model and the phononic states were calculated by a valence force field model. Then, transition probability was calculated by Fermi's golden rule, and Boltzmann's transport equation was solved for calculating lowfield mobility. The electron mobility of Ge NWs strongly depends on the wire orientations and cross-sectional shapes, and this dependence can be explained by the conduction band structure of Ge NWs. Among several geometries investigated in this paper, [110]-oriented NWs with wider width along [001] showed the highest electron mobility at low carrier concentration, and [112] NWs with wider width along [110] showed the highest electron mobility at high carrier concentration. This result indicates that these kinds of Ge NWs are suitable as n-channel material. © 1963-2012 IEEE.

DOI： 10.1109/TED.2014.2318896

Quantitative comparison between Z(1/2) center and carbon vacancy in 4H-SiC

Kawahara Koutarou, Xuan Thang Trinh, Nguyen Tien Son, Janzen Erik, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 115 ( 14 ) 2014.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

In this study, to reveal the origin of the Z1/2 center, a lifetime killer in n-type 4H-SiC, the concentrations of the Z1/2 center and point defects are compared in the same samples, using deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). The Z1/2 concentration in the samples is varied by irradiation with 250 keV electrons with various fluences. The concentration of a single carbon vacancy (VC) measured by EPR under light illumination can well be explained with the Z1/2 concentration derived from C-V and DLTS irrespective of the doping concentration and the electron fluence, indicating that the Z1/2 center originates from a single VC. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4871076

4H-SiC MISFETs With 4H-AlN Gate Insulator Isopolytypically Grown on 4H-SiC (11(2)over-bar0)

Horita Masahiro, Noborio Masato, Kimoto Tsunenobu, Suda Jun

IEEE ELECTRON DEVICE LETTERS Vol. 35 ( 3 ) page： 339 - 341 2014.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEEE Electron Device Letters

4H silicon carbide (4H-SiC) metal-insulator-semiconductor field-effect transistors (MISFETs) with 4H aluminum nitride (4H-AlN) gate insulators have been demonstrated. The 4H-AlN layers are isopolytypically grown on 4H-SiC (1120) by molecular-beam epitaxy. Gate controlled transistor operation was realized using the AlN/SiC MISFETs. The MISFETs exhibit a low gate leakage current (<10-10~A) and normally on characteristics with a threshold voltage of approximately-10~V and a field-effect mobility of 0.5 cm 2V-1s-1. Capacitance-voltage measurements of AlN/SiC MIS capacitors reveal a large negative flat band shift of-10.9~V, which is consistent with the normally on characteristics. © 2014 IEEE.

DOI： 10.1109/LED.2014.2299557

Effect of ultrathin AIN spacer on electronic properties of GaN/SiC heterojunction bipolar transistors

Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 53 ( 3 ) 2014.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

GaN/SiC heterojunction bipolar transistors (HBTs) with an ultrathin AlN spacer layer at the n-GaN/p-SiC emitter junction are proposed for the control of the electronic properties of GaN/SiC heterojunctions. The insertion of an AlN spacer is found to be promising in terms of improving electron injection efficiency owing to the reduced potential barrier (0.54 eV) to electron injection and reduced recombination via interface traps. We also investigated the effect of pre-irradiation of active nitrogen atoms (N*) prior to AlN growth for the control of the electronic properties of GaN/ AlN/SiC heterojunctions. We found that the potential barrier was further reduced to 0.46 eV by N* pre-irradiation. The HBT structure was successfully fabricated using our newly developed process featuring ion implantation and Pd ohmic contacts to obtain a low contact resistivity to a p-SiC base at a temperature as low as 600 °C. A fabricated HBT without an AlN layer showed a low current gain (α ∼ 0.001), whereas the GaN/ AlN/SiC HBT showed improved current gains of 0.1 in the case of using a 1-nm-thick AlN spacer without N* pre-irradiation and 0.2 in the case of using a 2-nm-thick AlN spacer with N* pre-irradiation. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.034101

Quantum-confinement effects on conduction band structure of rectangular cross-sectional GaAs nanowires

Tanaka H., Morioka N., Mori S., Suda J., Kimoto T.

JOURNAL OF APPLIED PHYSICS Vol. 115 ( 5 ) 2014.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

The conduction band structure and electron effective mass of GaAs nanowires with various cross-sectional shapes and orientations were calculated by two methods, a tight-binding method and an effective mass equation taking the bulk full-band structure into account. The effective mass of nanowires increases as the cross-sectional size decreases, and this increase in effective mass depends on the orientations and substrate faces of nanowires. Among [001], [110], and [111]-oriented rectangular cross-sectional GaAs nanowires, [110]-oriented nanowires with wider width along the [001] direction showed the lightest effective mass. This dependence originates from the anisotropy of the Γ valley of bulk GaAs. The relationship between effective mass and bulk band structure is discussed. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4864490

Identification of dislocations in 4H-SiC epitaxial layers and substrates using photoluminescence imaging

Kawahara Chihiro, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 53 ( 2 ) 2014.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Dislocations in n- and p-type substrates as well as in epitaxial layers (epilayers) were clearly identified using a photoluminescence (PL) imaging technique. Dislocations in epilayers show large/small bright spots or lines in infrared PL images, which correspond to threading screw/edge dislocations (TSDs/TEDs) or basal plane dislocations (BPDs), respectively. In contrast, dislocations in substrates exhibit large/small dark spots or dark lines in infrared PL images, corresponding to TSDs/TEDs or BPDs, respectively. These different features (bright/dark contrast) of dislocations may originate from the different densities of point defects or impurities. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.020304

Etching-limiting process and origin of loading effects in silicon etching with hydrogen chloride gas

Morioka Naoya, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 53 ( 1 ) 2014.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

The etching-limiting step in slow Si etching with HCl/H2 at atmospheric pressure was investigated. The etching was performed at a low etching rate below 10nm/min in the temperature range of 1000-1100 °C. In the case of bare Si etching, it was confirmed that the etching rate showed little temperature dependence and was proportional to the equilibrium pressure of the etching by-product SiCl2 calculated by thermochemical analysis. In addition, the etching rates of Si(100) and (110) faces were almost the same. These results indicate that SiCl2 diffusion in the gas phase is the rate-limiting step. In the etching of the Si surface with SiO2 mask patterns, a strong loading effect (mask/opening pattern dependence of the etching rate) was observed. The simulation of the diffusion of gas species immediately above the Si surface revealed that the loading effect was attributed to the pattern-dependent diffusion of SiCl2.© 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.016502

Conduction-Type Dependence of Thermal Oxidation Rate on SiC(0001)

Kobayashi Takuma, Suda Jun, Kimoto Tsunenobu

2014 IEEE INTERNATIONAL MEETING FOR FUTURE OF ELECTRON DEVICES, KANSAI (IMFEDK) 2014

Fabrication of electrostatically actuated 4H-SiC microcantilever resonators by using n/p/n epitaxial structures and doping-selective electrochemical etching

Sato K., Adachi K., Okamoto H., Yamaguchi H., Kimoto T., Suda J.

Materials Science Forum Vol. 778-780 page： 780 - 783 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Science Forum

We fabricated electrostatically actuated single-crystalline 4H-SiC microcantilever resonators. To realize a narrow gap between cantilevers and substrate, we etched a thin p-type SiC layer in n/p/n multilayer structure by doping-selective electrochemical etching. The resonant characteristics of the fabricated 4H-SiC microcantilevers were investigated under a vacuum condition. Electrostatic actuation of microcantilevers was successfully performed by applying 10 mVrms ac voltage with 20 mV dc bias. The quality factor of 4H-SiC microcantilevers was above 100,000, which is about ten times higher than the quality factor of Si cantilevers with the same structure. Resonant characteristics were almost identical for mechanical actuation and electrostatic actuation. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/MSF.778-780.780

Identification of the negative carbon vacancy at quasi-cubic site in 4H-SIC by EPR and theoretical calculations

Trinh X.T., Szász K., Hornos T., Kawahara K., Suda J., Kimoto T., Gali A., Janzén E., Son N.T.

Materials Science Forum Vol. 778-780 page： 285 - 288 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Science Forum

In freestanding n-type 4H-SiC epilayers irradiated with low-energy (250 keV) electrons at room temperature, the electron paramagnetic resonance (EPR) spectrum of the negative carbon vacancy at the hexagonal site, V-C(h), and a new signal were observed. From the similarity in defect formation and the spin-Hamiltonian parameters of the two defects, the new center is suggested to be the negative C vacancy at the quasi-cubic site, V-C (k). The identification is further supported by hyperfine calculations. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/MSF.778-780.285

Ion Implantation Technology in SiC for Power Device Applications

Kimoto Tsunenobu, Kawahara Koutaro, Niwa Hiroki, Kaji Naoki, Suda Jun

2014 INTERNATIONAL WORKSHOP ON JUNCTION TECHNOLOGY (IWJT) page： 1 - 6 2014

Orientation and Size Effects on Phonon-limited Hole Mobility in Rectangular Cross-sectional Germanium Nanowires

Tanaka Hajime, Mori Seigo, Morioka Naoya, Suda Jun, Kimoto Tsunenobu

2014 IEEE SILICON NANOELECTRONICS WORKSHOP (SNW) 2014

Ion implantation technology in SiC for power device applications

Kimoto T., Kawahara K., Niwa H., Kaji N., Suda J.

2014 International Workshop on Junction Technology, IWJT 2014 page： 1 - 6 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2014 International Workshop on Junction Technology, IWJT 2014

Silicon carbide (SiC) is a newly-emerging wide bandgap semiconductor, by which high-voltage, low-loss power devices can be realized owing to its superior properties. Because of its strong bonding energy and thermal stability, however, special cares must be paid to form high-quality junctions by ion implantation. This paper reviews present status and remaining issues of ion implantation technology in SiC. Requirements of hot implantation and high-temperature annealing are discussed in terms of electrical activation, defect generation, and junction characteristics. Furthermore, recent progress in junction termination for high-voltage SiC devices by using ion implantation is described. © 2014 IEEE.

DOI： 10.1109/IWJT.2014.6842018

100 mm diameter mono-crystalline 4H-SiC/polycrystalline-SiC bonded wafers fabricated by SAB for power device

Yagi K., Hatta N., Sakata T., Minami A., Kawahara T., Uchida H., Imaoka K., Okuda T., Suda J., Kurashima Y., Takagi H.

Proceedings of 2014 4th IEEE International Workshop on Low Temperature Bonding for 3D Integration, LTB-3D 2014 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of 2014 4th IEEE International Workshop on Low Temperature Bonding for 3D Integration, LTB-3D 2014

We have developed 100mm in diameter 4H-SiC/poly-SiC bonded wafer by SAB method. The SiC bonded wafer demonstrated an excellent thermal stability against device processing temperature. SBDs fabricated on the SiC bonded wafer exhibited good I-V characteristics. These results suggest that it is a promising alternative wafer for SiC power device. © 2014 IEEE.

DOI： 10.1109/LTB-3D.2014.6886195

100 mm diameter mono-crystalline 4H-SiC/polycrystalline-SiC bonded wafers fabricated by SAB for power device

Yagi Kuniaki, Hatta Naoki, Sakata Toyokazu, Minami Akiyuki, Kawahara Takamitsu, Uchida Hidetsugu, Imaoka Kou, Okuda Takafumi, Suda Jun, Kurashima Yuichi, Takagi Hideki

2014 4TH IEEE INTERNATIONAL WORKSHOP ON LOW TEMPERATURE BONDING FOR 3D INTEGRATION (LTB-3D) page： 56 - 56 2014

Progress in Ultrahigh-Voltage SiC Devices for Future Power Infrastructure

Kimoto T., Suda J., Yonezawa Y., Asano K., Fukuda K., Okumura H.

2014 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM) 2014

Negative-U carbon vacancy in 4H-SiC: Assessment of charge correction schemes and identification of the negative carbon vacancy at the quasicubic site

Trinh X. T., Szasz K., Hornos T., Kawahara K., Suda J., Kimoto T., Gali A., Janzen E., Son N. T.

PHYSICAL REVIEW B Vol. 88 ( 23 ) 2013.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physical Review B - Condensed Matter and Materials Physics

The carbon vacancy (VC) has been suggested by different studies to be involved in the Z1/Z2 defect-a carrier lifetime killer in SiC. However, the correlation between the Z1/Z2 deep level with VC is not possible since only the negative carbon vacancy (VC-) at the hexagonal site, VC-(h), with unclear negative-U behaviors was identified by electron paramagnetic resonance (EPR). Using freestanding n-type 4H-SiC epilayers irradiated with low energy (250 keV) electrons at room temperature to introduce mainly VC and defects in the C sublattice, we observed the strong EPR signals of VC-(h) and another S = 1/2 center. Electron paramagnetic resonance experiments show a negative-U behavior of the two centers and their similar symmetry lowering from C3v to C1h at low temperatures. Comparing the 29Si and 13C ligand hyperfine constants observed by EPR and first principles calculations, the new center is identified as VC-(k). The negative-U behavior is further confirmed by large scale density functional theory supercell calculations using different charge correction schemes. The results support the identification of the lifetime limiting Z1/Z2 defect to be related to acceptor states of the carbon vacancy. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.235209

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