Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Temperature dependence of electrical properties of NiO thin films for Resistive Random Access Memory

Suzuki Ryota, Suda Jun, Kimoto Tsunenobu

MATERIALS SCIENCE AND TECHNOLOGY FOR NONVOLATILE MEMORIES Vol. 1071 page： 69 - 74 2008

Fabrication and electronic characteristics of silicon nanowire mosfets

Yoshioka H., Nanen Y., Suda J., Kimoto T.

Materials Research Society Symposium Proceedings Vol. 1080 page： 90 - 95 2008

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

The n-type silicon nanowire MOSFETs with a nanowire shape being triangular or trapezoidal, have been fabricated on SOI substrates and characterized. The height and bottom-width of the triangular nanowire has been 10 nm and 19 nm, respectively. The devices have shown good gate control, such as a nearly ideal subthreshold slope of 63 mV/decade, high Ion/Ioff ratio of 107, and small drain-induced barrier lowering of 5 mV/V at room temperature. The low field mobility of triangular nanowire has been estimated to be 130 cm2/V·s and shown no difference with the change of the nanowire shape and direction within the investigated range. © 2008 Materials Research Society.

DOI： 10.1557/proc-1080-o12-02

Temperature dependence of electrical properties of NiO thin films for resistive random access memory

Suzuki R., Suda J., Kimoto T.

Materials Research Society Symposium Proceedings Vol. 1071 page： 69 - 74 2008

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Temperature dependence of electrical properties in NiO thin films for ReRAM applications has been investigated. I-V measurements have been carried out in the temperature range from 100K to 523K. The resistance in the high resistance state (HRS) is almost independent of temperature below 250K, whereas it decreases with an activation energy of 300 meV above 250K. Hopping conduction and band conduction may be dominant in the low- and high-temperature range, respectively. Admittance spectroscopy on the NiO/n+-Si structure reveals the existence of a high density of traps, which may contribute to the conduction in HRS. In the low resistance state (LRS), however, the resistance slightly increased in the whole temperature range and the trend is similar to that of metallic Ni film, indicating the metallic Ni defects is related to the conduction in LRS. The Pt/NiO/Pt structure demonstrated stable resistance switching even at temperature as high as 250°C or higher. Since other competitive nonvolatile memories will face severe difficulty in high-temperature operation, the present ReRAM shows promise for high-temperature application. © 2008 Materials Research Society.

DOI： 10.1557/proc-1071-f08-08

4H-SiC lateral double RESURF MOSFETs with low ON resistance

Noborio Masato, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 54 ( 5 ) page： 1216 - 1223 2007.5

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

Designing and fabrication of 4H-SiC (0001) lateral MOSFETs with a double reduced surface field (RESURF) structure have been investigated to reduce on resistance. In order to achieve high breakdown voltage, a two-zone RESURF structure was also employed in addition to the double RESURF structure. The simulated double RESURF MOSFETs with optimum doses exhibit slightly higher breakdown voltage and lower drift resistance than the simulated single RESURF MOSFETs. The double RESURF structure is attractive to suppress oxide breakdown at gate edge. After the device simulation for dose optimization, the 4H-SiC two-zone double RESURF MOSFETs have been fabricated by using a self-aligned process. The fabricated MOSFET has demonstrated a high breakdown voltage of 1380 V and a low on resistance of 66 mΩ · cm2 (including a drift resistance of 24 mΩ · cm2). The drift resistance of the fabricated double RESURF MOSFETs is only 50% or even lower than that of the single RESURF MOSFETs. © 2007 IEEE.

DOI： 10.1109/TED.2007.894249

A comparative study of nonpolar a-plane and m-plane AlN grown on 4H-SiC by plasma-assisted molecular-beam epitaxy

Suda J., Horita M., Armitage R., Kimoto T.

JOURNAL OF CRYSTAL GROWTH Vol. 301 ( SPEC. ISS. ) page： 410 - 413 2007.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

AlN has been grown on 4H-SiC m-plane (1 over(1, -) 0 0) and a-plane (1 1 over(2, -) 0) substrates by RF-plasma-assisted molecular-beam epitaxy. Similarities and differences between the two growth orientations are discussed. High-quality AlN can be obtained in both orientations when grown in the metastable 4H-crystal structure. For both epilayer orientations Al-rich conditions were necessary to stabilize the 4H-polytype. 4H-AlN for both growth directions shows very narrow X-ray rocking curves widths less than 100 arcsec. a-plane 4H-AlN exhibited a much smoother morphology than m-plane 4H-AlN. On the other hand, reflection high-energy diffraction intensity oscillations in the initial growth stage were observed only for m-plane AlN. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2006.11.287

Reduction in potential barrier height of AlGaN/GaN heterostructures by SiN passivation

Onojima N., Higashiwaki M., Suda J., Kimoto T., Mimura T., Matsui T.

JOURNAL OF APPLIED PHYSICS Vol. 101 ( 4 ) 2007.2

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

SiN passivation on AlGaNGaN heterostructures was carried out using catalytic or plasma-enhanced chemical vapor deposition (Cat-CVD or PECVD), which has been found to increase two-dimensional electron gas (2DEG) density. The 2DEG density can be closely related to AlGaN surface properties via polarization effects. AlGaN potential barrier heights of AlGaNGaN heterostructures with and without SiN passivation were systematically investigated using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) measurements. The results for the XPS and C-V measurements were consistent and demonstrated that a reduction in the AlGaN potential barrier height was actually induced by SiN passivation. Furthermore, Cat-CVD SiN passivation lowered the AlGaN potential barrier height more significantly than PECVD SiN passivation did, suggesting that the passivation method can influence the AlGaN potential barrier height. © 2007 American Institute of Physics.

DOI： 10.1063/1.2472255

m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates

Armitage R., Horita M., Suda J., Kimoto T.

JOURNAL OF APPLIED PHYSICS Vol. 101 ( 3 ) 2007.2

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

A series of m -plane GaN layers with the Ga beam-equivalent pressure (BEP) as the only varied parameter was grown by rf-plasma assisted molecular beam epitaxy on m -plane 4H-SiC substrates using AlN buffer layers. The smoothest growth surfaces and most complete film coalescence were found for the highest Ga BEP corresponding to the Ga droplet accumulation regime. However, better structural quality as assessed by x-ray rocking curves was observed for growth at a lower Ga BEP value below the droplet limit. The variation of rocking curve widths for planes inclined with respect to the epilayer c axis followed a different trend with Ga BEP than those of reflections parallel to the c axis. The GaN layers were found to exhibit a large residual compressive strain along the a axis. © 2007 American Institute of Physics.

DOI： 10.1063/1.2435806

Accurate determination of nonlinear optical coefficients of hexagonal silicon carbide of polytype 6H

Abe M., Maruyama K., Sato H., Tanaka H., Suda J., Shoji I., Kondo T.

Optics InfoBase Conference Papers 2007

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Optics InfoBase Conference Papers

Nonlinear optical coefficients of 6H-SiC have been measured with much improved accuracy using high quality single crystalline plane-parallel plates by the Maker-fringe technique combined with theoretical analysis taking into account of the multiple-reflection effect. © 2007 Optical Society of America.

DOI： 10.1364/nlo.2007.we25

Lateral 4H-SiC MOSFETs with low on-resistance by using two-zone double RESURF structure

Noborio M., Suda J., Kimoto T.

Materials Science Forum Vol. 556-557 page： 815 - 818 2007

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

4H-SiC lateral MOSFETs with a double reduced surface field (RESURF) structure have been fabricated in order to reduce drift resistance. A two-zone RESURF structure was also employed in addition to double RESURF structure for achieving both high breakdown voltage and low on-resistance. After device simulation for dose optimization, 4H-SiC two-zone double RESURF MOSFETs have been fabricated. The fabricated MOSFETs block 1380 V and exhibit a low on-resistance of 66 mΩcm2 (including a drift resistance of 24 mΩcm2) at a gate oxide field of 3 MV/cm. The figure-of-merit of present device is about 29 MW/cm2, which is the best performance among any lateral MOSFETs. The drift resistance of the fabricated double RESURF MOSFETs is only 50% or even lower than that of single RESURF MOSFETs. Temperature dependence of device characteristics is also discussed.

DOI： 10.4028/www.scientific.net/MSF.556-557.815

Lateral 4H-SiC MOSFETs with low on-resistance by using two-zone double RESURF structure

Noborio M., Suda J., Kimoto T.

Materials Science Forum Vol. 556-557 page： 815 - 818 2007

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

4H-SiC lateral MOSFETs with a double reduced surface field (RESURF) structure have been fabricated in order to reduce drift resistance. A two-zone RESURF structure was also employed in addition to double RESURF structure for achieving both high breakdown voltage and low on-resistance. After device simulation for dose optimization, 4H-SiC two-zone double RESURF MOSFETs have been fabricated. The fabricated MOSFETs block 1380 V and exhibit a low on-resistance of 66 Ωcm2 (including a drift resistance of 24 mΩcm2) at a gate oxide field of 3 MV/cm. The figure-of-merit of present device is about 29 MW/cm2, which is the best performance among any lateral MOSFETs. The drift resistance of the fabricated double RESURF MOSFETs is only 50 % or even lower than that of single RESURF MOSFETs. Temperature dependence of device characteristics is also discussed.

DOI： 10.4028/0-87849-442-1.815

Impact of acceptor concentration on electronic properties of n<sup>+</sup>-GaN/p<sup>+</sup>-SiC heterojunction for gan/sic heterojunction bipolar transistor

Amari K., Suda J., Kimoto T.

Materials Science Forum Vol. 556-557 page： 1039 - 1042 2007

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

The electrical properties of n+-GaN/p+-SiC heterojunction diodes have been investigated by varying the acceptor concentration of p+-SiC epilayers (Na) and polytype of SiC (4H- and 6H-SiC). The current-voltage (I-V) characteristics of diodes with Na ~ 1x1019 cm-3 were dominated by tunneling-assisted current. The diodes with Na ~ 1x1018 cm-3 exhibit excellent characteristics and 6H-SiC may be a better choice from a view point of electron injection into p-SiC base. Compared to previous investigations (Na<1016cm-3), we could obtain good rectification with p-SiC doped to two-order-of-magnitude higher acceptor concentration.

DOI： 10.4028/www.scientific.net/MSF.556-557.1039

Impact of acceptor concentration on electronic properties of n <sup>+</sup>-GaN/p<sup>+</sup>-SiC heterojunction for GaN/SiC heterojunction bipolar transistor

Amari K., Suda J., Kimoto T.

Materials Science Forum Vol. 556-557 page： 1039 - 1042 2007

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

The electrical properties of n+-GaN/p+-SiC heterojunction diodes have been investigated by varying the acceptor concentration of P+-SiC epilayers (Na) and polytype of SiC (4H- and 6H-SiC). The current-voltage (I-V) characteristics of diodes with Na ∼1×1019 cm-3 were dominated by tunneling-assisted current. The diodes with Na ∼ 1×10 18 cm-3 exhibit excellent characteristics and 6H-SiC may be a better choice from a view point of electron injection into p-SiC base. Compared to previous investigations (Na<1016cm -3), we could obtain good rectification with p-SiC doped to two-order-of-magnitude higher acceptor concentration.

DOI： 10.4028/0-87849-442-1.1039

Dose designing and fabrication of 4H-SiC double RESURF MOSFETs

Noborio M., Suda J., Kimoto T.

Proceedings of the International Symposium on Power Semiconductor Devices and ICs Vol. 2006 2006.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of the International Symposium on Power Semiconductor Devices and ICs

Designing and fabrication of 4H-SiC (0001) lateral MOSFETs with a double reduced surface field (RESURF) structure have been investigated to reduce a drift resistance. In order to achieve high breakdown voltage, a two-zone RESURF structure was also employed In addition to the double RESURF structure. After device simulation for dose optimization, 4H-SiC two-zone double RESURF MOSFETs have been fabricated by using an original self-aligned process proposed in this paper. The fabricated MOSFETs with optimum doses exhibit a high breakdown voltage of 1380 V and a low on-resistance of 66 mΩcm2 (including a drift resistance of 13 mΩcm2). The drift resistance in the fabricated MOSFETs with double RESURF structure is only 50 % or even lower than that in the MOSFETs with a normal RESURF structure. The figure-of-merit (VB2/RON) of the present device reaches 29 MW/cm2, which is the best performance among any lateral MOSFETs ever reported. ©2006 IEEE.

High-quality nonpolar 4H-AlN grown on 4H-SiC (11(2)over-bar20) substrate by molecular-beam epitaxy

Horita Masahiro, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS LETTERS Vol. 89 ( 11 ) 2006.9

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

Growth of very high-quality nonpolar (112̄0) a-plane face 4H-AlN on 4H-SiC (112̄0) substrate was investigated. Nonpolar 4H-AlN (112̄0) was isopolytypically grown on 4H-SiC (112̄0) substrate by molecular-beam epitaxy. A reduction of defects such as stacking faults and threading dislocations was achieved by keeping the growing surface flat. To this end, the SiC substrate was HCl gas etched and the V/III ratio was optimized for AlN growth. A full width at half maximum of symmetrical x-ray diffraction ω scan of the 4H-AlN layer was 40 arc sec. Transmission electron microscopy revealed the stacking fault density to be 2 × 105 cm -1, and the partial and perfect threading dislocation densities to be 7 × 107 and 1 × 107 cm-2, respectively. © 2006 American Institute of Physics.

DOI： 10.1063/1.2352713

Growth of nonpolar AlN and AlGaN on 4H-SiC (1-100) by molecular beam epitaxy

Armitage R., Horita M., Suda J., Kimoto T.

Materials Research Society Symposium Proceedings Vol. 892 page： 705 - 710 2006.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

AlN and AlGaN have been grown on 4H-SiC (1-100) substrates by rf-plasma molecular beam epitaxy. AlN assumes a metastable 4H structure to match the in-plane stacking arrangement of the substrate. Initial 2D nucleation of 4H-AlN is revealed by reflection high-energy electron diffraction. The epitaxial quality is evidenced by narrow x-ray diffraction co-scan line widths less than 100 arcsec for symmetric and asymmetric reflections. Structural characterization results for AlGaN/AlN multiple quantum wells are also presented. © 2006 Materials Research Society.

Extremely high quantum efficiency of donor-acceptor-pair emission in N-and-B-doped 6H-SiC

Kamiyama S., Maeda T., Nakamura Y., Iwaya M., Amano H., Akasaki I., Kinoshita H., Furusho T., Yoshimoto M., Kimoto T., Suda J., Henry A., Ivanov I. G., Bergman J. P., Monemar B., Onuma T., Chichibu S. F.

JOURNAL OF APPLIED PHYSICS Vol. 99 ( 9 ) 2006.5

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

High-efficiency visible light emission in N-and-B-doped 6H-SiC epilayers was observed in photoluminescence measurements at room temperature. The orange-yellow light emission due to the recombination of donor-acceptor pairs (DAPs) has a broad spectrum with a peak wavelength of 576 nm and a full width at half maximum of 110 nm at 250 K. The high B concentration of more than 1018 cm-3 improves the emission efficiency of the DAP recombination at a high temperature. Compared with the photoluminescence spectrum of GaN at 10 K, a high quantum efficiency of 95% was estimated for the highly B-doped sample. From time-resolved photoluminescence measurements, a DAP recombination time of 5.0 ms was obtained, which is in good agreement with the calculated value by the rate equation with the assumption of a 95% internal quantum efficiency. This is quite promising as a light-emitting medium by optical pumping, as well as monolithic light sources combined with nitride-based light-emitting diodes grown on the DA-doped SiC epilayer. © 2006 American Institute of Physics.

DOI： 10.1063/1.2195883

Structure analysis of ZrB2(0001) surface prepared by ex situ HF treatment

Suto Hirofumi, Fujii Shunjiro, Miyamae Nobuhiko, Armitage Robert D., Suda Jun, Kimoto Tsunenobu, Honda Shin-ichi, Katayama Mitsuhiro

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 45 ( 17-19 ) page： L497 - L500 2006.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 2: Letters

The surface structure of ZrB2(0001) was investigated using coaxial impact-collision ion scattering spectroscopy (CAICISS). The ZrB 2(0001) 1 × 1 surface was prepared by HF solution treatment and annealing in vacuum. It was directly evidenced that the ZrB2(0001) surface is terminated with a Zr layer. Moreover, we found that the interlayer spacing between the first Zr layer and the second B layer is expanded by 20% with regard to c-axis lattice constant. Since small amount of O atoms were detected after the cleaning, the incorporation of the residual O atoms into the subsurface region of the ZrB2(0001) surface is likely to be the origin of the large expansion. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.L497

Characterization of ZrB2(0001) surface prepared by ex situ HF solution treatment toward applications as a substrate for GaN growth

Armitage R, Suda J, Kimoto T

SURFACE SCIENCE Vol. 600 ( 7 ) page： 1439 - 1449 2006.4

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

ZrB2(0 0 0 1) crystals grown by the rf-floating zone technique were characterized by X-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and atomic force microscopy. These characteristics were investigated as a function of thermal cleaning temperature up to 1000 °C in vacuum for as-received substrates as well as substrates treated ex situ in HF aqueous solution. The HF treatment process removed the ZrO2 native oxide layer present on as-received substrates and resulted in ZrB2(0 0 0 1) surfaces exhibiting long-range order. Upon annealing the HF-treated surface in high vacuum, two types of reconstructions were observed: an incommensurate reconstruction from 650 to 900°C related to residual H 2 gas, and n × n reconstructions at 1000°C, possibly related to oxygen. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2006.01.032

Epitaxy of nonpolar AlN on 4H-SiC (1-100) substrates

Armitage R, Suda J, Kimoto T

APPLIED PHYSICS LETTERS Vol. 88 ( 1 ) 2006.1

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

AlN has been grown on 4H-SiC (1-100) substrates by rf-plasma molecular beam epitaxy. The epilayers assume a metastable 4H structure to match the in-plane stacking arrangement of the substrate. Initial two-dimensional nucleation of 4H-AlN is revealed by reflection high-energy electron diffraction. The epitaxial quality is evidenced by narrow x-ray diffraction ω-scan linewidths less than 70 arcsec for both symmetric and asymmetric reflections. The AlN growth surface exhibits a smooth and anisotropic morphology similar to that of GaN (1-100). Large residual stress is present in the epilayers, consistent with incomplete relaxation of misfit strain during growth. © 2006 American Institute of Physics.

DOI： 10.1063/1.2161809

Anisotropic etching of single crystalline SiC using molten KOH for SiC bulk micromachining

Fukunaga Katsuhiko, Suda Jun, Kimoto Tsunenobu

MICROMACHINING AND MICROFABRICATION PROCESS TECHNOLOGY XI Vol. 6109 2006

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Microelectromechanical systems (MEMS) devices made of single crystalline silicon carbide (SiC) are attractive for applications in harsh environment, because SiC is chemically inert and semiconductor devices made of SiC can be operated at very high temperature. On the other hand, due to its chemical inertness, controllable etching of SiC has been difficult. Molten KOH etching has been widely used to detect crystalline defects in SiC as etch pit in crystal growth researchers. Some etch pits have hexagonal shape, indicating anisotropic etching nature. Therefore, molten KOH etching may have potential as a SiC MEMS fabrication process. In this study we have developed the anisotropic wet chemical etching of single crystalline hexagonal SiC using molten KOH for SiC bulk micromachining, 6H-SiC (0001)Si face and (000-1)C face substrates are used. Etching rates of (0001)Si and (000-1)C faces at 490°C are evaluated to be 37 nm/min and 3.1 μm/min, respectively, indicating that the (0001)Si face is etched almost 100 times slower than the (000-1)C face is. Cross sectional analysis of etched structure of (000-1)C face revealed that inclined crystal plane was formed as a sidewall with some undercut. To assess in-plane etching anisotropy, ring shape mesa structures are formed on SiC (0001)Si face by R1E and then etched by molten KOH, Ring shape changed into hexagonal shape, clearly indicating etching rate along 〈11-20〉 direction is larger than 〈1-100〉 direction in (0001)Si face.

DOI： 10.1117/12.647116

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