Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Electron injection from GaN to SiC and fabrication of GaN/SiC heterojunction bipolar transistors

Suda J., Nakano Y., Shimada S., Amari K., Kimoto T.

Materials Science Forum Vol. 527-529 ( PART 2 ) page： 1545 - 1548 2006

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

Characterization of n+-GaN/p--SiC and n +-GaN/p+-SiC heterojunctions as well as fabrication of GaN/SiC heterojunction bipolar transistors (HBTs) using these heterojunctions is presented. The electroluminescence spectrum from n+-GaN/p +-SiC heterojunction diodes under forward bias clearly indicates electron injection from n+-GaN into P+-SiC. HBTs consisting of n+-GaN emitter /p+-SiC base/n --SiC collector/n+-SiC substrate have been fabricated. Although clear common-base properties were obtained, the current gain was very low (10-4). SiC homojunction bipolar junction transistors (BJT) using the same base-collector junction exhibited a current gain value of 0.5, suggesting the low current gain of GaN/SiC HBTs originates from low emitter efficiency.

DOI： 10.4028/0-87849-425-1.1545

Low-dislocation-density nonpolar AlN grown on 4H-SiC (11-20) substrates

Suda J., Horita M., Kimoto T.

Materials Research Society Symposium Proceedings Vol. 955 page： 61 - 62 2006

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

Growth of AlN on 4H-SiC (11-20) substrates by plasma-assisted molecular-beam epitaxy is presented. Very high-quality AlN can be grown under a slightly Al-rich condition. Transmission electron microscopy revealed that the AlN layer has 4H crystalline structure with high-phase purity (stacking-fault density of 2×105cm-1) and the density of threading dislocations is as small as 8×107cm-2. © 2007 Materials Research Society.

DOI： 10.1557/proc-0955-i06-03

Improved dielectric and interface properties of 4H-SiC MOS structures processed by oxide deposition and N<inf>2</inf>O annealing

Kimoto T., Kawano H., Noborio M., Suda J., Matsunami H.

Materials Science Forum Vol. 527-529 ( PART 2 ) page： 987 - 990 2006

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

Oxide deposition followed by high-temperature annealing in N2O has been investigated to improve the quality of 4H-SiC MOS structures. Annealing of deposited oxides in N2O at 1300°C significantly enhances the breakdown strength and decreases the interface state density to 3×10" cm-2 eV-1 at Ec- 0.2 eV. As a result, high channel mobility of 34 cm2/Vs and 52 cm2/Vs has been attained for inversion-type MOSFETs fabricated on 4H-SiC(0001)Si and (000-1)C faces, respectively. The channel mobility shows a maximum when the increase of oxide thickness during N2O annealing is approximately 5 nm. A lateral RESURF MOSFET with gate oxides formed by the proposed process has blocked 1450 V and showed a low on-resistance of 75 mΩcm2, which is one of the best performances among lateral SiC MOSFETs reported.

DOI： 10.4028/0-87849-425-1.987

Reduction of on-resistance in 4H-SiC multi-RESURF MOSFETs

Noborio M., Negoro Y., Suda J., Kimoto T.

Materials Science Forum Vol. 527-529 ( PART 2 ) page： 1305 - 1308 2006

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

SiC lateral MOSFETs with multi-RESURF structures have been fabricated by a self-aligned process. The "multi-RESURF" means "double RESURF" and "buried-p RESURF" structures, which have the buried-p region at the top and at the middle of RESURF region, respectively. The increase of net RESURF dose and the decrease of channel length lead to the reduced on-resistance. The "buried-p RESURF" MOSFETs have higher on-resistances than the "double RESURF" MOSFETs, due to the resistance of parasitic JFET inside the RESURF region. The dose designing for double RESURF MOSFETs has been optimized by using device simulation. A double RESURF MOSFET exhibits a breakdown voltage of 750 V and an on-resistance of 52 mΩcm2.

DOI： 10.4028/0-87849-425-1.1305

1200 V-Class 4H-SiC RESURF MOSFETs with low on-resistances

Kimoto T., Kawano H., Suda J.

Proceedings of the International Symposium on Power Semiconductor Devices and ICs page： 279 - 282 2005.11

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

4H-SiC{0001} RESURF MOSFETs with a two-zone structure have been simulated and fabricated. The dose dependencies of experimental breakdown voltage show good agreement with simulation. Through the optimization of implant dose, high-temperature (1700°C) annealing after ion implantation, and reduction of channel length, a high breakdown voltage of 1330 V and a low on-resistance of 69 mΩcm2 have been obtained. The 4H-SiC(000-1) face is promising for MOS-based devices owing to superior quality of MOS interface, and a performance of 1260 V - 62 mΩcm2 has been achieved. The figure-of-merit (VB2/Ron) of the present devices reaches 26 MW/cm2, being the best performance among lateral SiC MOSFETs reported. ©2005 IEEE.

Molecular-beam epitaxy of AlN on off-oriented SiC and demonstration of MISFET using AlN/SiC interface

Onojima N., Kaido J., Suda J., Kimoto T.

Physica Status Solidi C: Conferences Vol. 2 ( 7 ) page： 2643 - 2646 2005.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi C: Conferences

Molecular-beam epitaxy (MBE) of AlN on 4H-SiC epilayers with the off-cut angle of 8° was performed using elemental Al and rf-plasma excited active nitrogen (N*) toward the goal of MISFETs using the AlN/4H-SiC hetero-interface. AlN films grown at 600 °C had a very flat surface with monolayer-height steps. Control of atomic arrangement at the AlN/4H-SiC interface was attempted by pre-irradiation of active nitrogen to achieve MIS structures with excellent electrical characteristics. The electronic properties of AlN/4H-SiC interface were characterized by C-V measurements of Al/AlN/n-type 4H-SiC MIS capacitors. The interface states at the AlN/4H-SiC interface were revealed to be strongly influenced by preirradiation of active nitrogen. Planar-type n-channel AlN/4H-SiC MISFETs were fabricated using a gate-stacked structure with SiO2. Owing to the novel device structure as well as an optimized AlN growth condition, we could first demonstrate the good transistor operation of MISFETs using the AlN/4H-SiC interface. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200461526

Role of initial nucleation in molecular-beam epitaxy of GaN on lattice-matched ZrB<inf>2</inf> substrates

Armitage R., Suda J., Kimoto T.

Physica Status Solidi C: Conferences Vol. 2 ( 7 ) page： 2191 - 2194 2005.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi C: Conferences

Nitrogen-polar GaN was grown on lattice-matched ZrB2 substrates by a two-step rf-MBE process with conventional low-temperature GaN (LT-GaN) used as the nucleation layer. For nucleation in slightly Ga-rich conditions, a streaky RHEED pattern was maintained from the very beginning and persisted through-out subsequent high-temperature growth. However, despite the streaky RHEED pattern the initial nucleation was evidently not 2D as inferred from AFM and x-ray results. For nucleation in slightly N-rich conditions, spots appeared in the RHEED in the early stages of growth but a streak pattern was restored with high-temperature GaN growth. Tradeoffs were identified in optimizing the LT-GaN nucleation process. Slightly Ga-rich nucleation conditions offered the best x-ray characteristics with ω-scan FWHM values of 400-500 and 720-800 arcsec for the (0002) and (11̄04) reflections, respectively. Short-length atomic steps (up to ∼200 nm) were present on the surfaces of such layers, but the morphology showed a sub-grain structure. Slightly N-rich nucleation conditions yielded remarkably smooth films surfaces (rms 0.5 nm over 10 μm2) with uninterrupted atomic steps up to several urn long, but inferior x-ray ω-scans (∼50% larger FWHM values). © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200461539

Direct growth of GaN on off-oriented SiC (0001) by molecular-beam epitaxy for GaN/SiC heterojunction bipolar transistor

Nakano Y., Suda J., Kimoto T.

Physica Status Solidi C: Conferences Vol. 2 ( 7 ) page： 2208 - 2211 2005.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi C: Conferences

Direct growth of GaN on misoriented 4H- and 6H-SiC (0001) Si-face substrates and electrical characteristics of n-GaN/p-SiC heterojunction mesa diodes are presented. GaN was grown by molecular-beam epitaxy (MBE) using elemental Ga and rf plasma-excited active nitrogen. SiC substrates misoriented 8° toward the [11-20] direction were used in this study. The surfaces of MBE-grown GaN layers have wavy features with peak-to-valley height of 30 nm. These features originated from the substrate misorientation. It was found that step bunching and large faceting along [01-10] and [10-10] directions occurred during the growth of GaN. Lowering the growth temperature suppresses large faceting, and results in reduction of the peak-to-valley height to 3 nm. However, the surface still has the same undulating features (on a smaller length scale). Mesa diodes were fabricated from the grown GaN layers. The correlation between the diode electrical characteristics and GaN growth conditions is discussed. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200461549

Mechanism of stabilization of zincblende GaN on hexagonal substrates: Insight gained from growth on ZrB2(0001)

Armitage R, Nishizono K, Suda J, Kimoto T

JOURNAL OF CRYSTAL GROWTH Vol. 284 ( 3-4 ) page： 369 - 378 2005.11

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

Thin (∼25 nm) zincblende GaN (1 1 1) epilayers have been grown on hexagonal ZrB2 (0 0 0 1) substrates by plasma-assisted molecular-beam epitaxy at temperatures near 600 °C. Layers grown in near-stoichiometric conditions exhibit high phase purity; no wurtzite inclusions are detected by high-resolution X-ray diffraction or photoluminescence. For growth in the presence of excess Ga the layers are predominantly zincblende phase, but contain some wurtzite inclusions. Reducing the growth temperature to 400 °C results in a much-increased fraction of wurtzite inclusions. The growth of zincblende GaN with high phase purity on hexagonal ZrB2 implies the existence of an underlying physical mechanism rather than simply a result of "growth mistakes." A possible surface energy-related mechanism by which zincblende GaN (1 1 1) can be preferentially nucleated on hexagonal substrates is discussed. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2005.07.037

1330 V, 67 m Omega center dot cm(2) 4H-SiC(0001) RESURF MOSFET

Kimoto T, Kawano H, Suda J

IEEE ELECTRON DEVICE LETTERS Vol. 26 ( 9 ) page： 649 - 651 2005.9

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

Design and fabrication of 4H-SiC(0001) lateral MOSFETs with a two-zone reduced surface field structure have been investigated. The dose dependencies of experimental breakdown voltage show good agreement with simulation. Through the optimization of implant dose, high-temperature (1700 °C) annealing after ion implantation, and reduction of channel length, a breakdown voltage of 1330 V and a low on-resistance of 67 mΩ · cm2 have been obtained. The figure-of-merit (VB2/Ron) of the present device reaches 26 MW/cm2, being the best performance among lateral MOSFETs reported. The temperature dependence of static characteristics is also presented. © 2005 IEEE.

DOI： 10.1109/LED.2005.854371

Experimental and theoretical investigations on short-channel effects in 4H-SiC MOSFETs

Noborio M, Kanzaki Y, Suda J, Kimoto T

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 52 ( 9 ) page： 1954 - 1962 2005.9

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

In this paper, a fundamental investigation on short-channel effects (SCEs) in 4H-SiC MOSFETs is given. Planar MOSFETs with various channel lengths have been fabricated on p-type 4H-SiC (0001), (0001̄) and (112̄0) faces. In the fabricated MOSFETs, SCEs such as punchthrough behavior, decrease of threshold voltage, deterioration of subthreshold characteristics, and saturation of transconductance occur by reducing channel length. The critical channel lengths below which SCEs occur are analyzed as a function of p-body doping and oxide thickness by using device simulation. The critical channel lengths obtained from the device simulation is in good agreement with the empirical relationship for Si MOSFETs. The critical channel lengths in the fabricated SiC MOSFETs are slightly longer than simulation results. The dependence of crystal face orientations on SCEs is hardly observed. Impacts of interface charge on the appearance of SCEs are discussed. © 2005 IEEE.

DOI： 10.1109/TED.2005.854269

Influence of substrate misorientation angle and direction in growth of GaN on off-axis SiC (0001)

Suda J., Nakano Y., Kimoto T.

Materials Research Society Symposium Proceedings Vol. 831 page： 471 - 476 2005.8

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

Growth of GaN on 4H- or 6H-SiC (0001) Si-face substrates with various misorientation angles and directions is presented. GaN layers were directly grown on the SiC substrates by molecular-beam epitaxy using elemental Ga and rf plasma-excited active nitrogen. First, 4H-SiC (0001) 8o-off toward the [11-20] direction was investigated. Before the growth of GaN, ex-situ high-temperature gas etching was carried out, resulting in a smooth SiC initial surface. However, the surface of the subsequently grown GaN layer has wavy features with peak-to-valley height of 30 nm. Since the direction of the undulations is parallel to the misorientation direction, this feature must originate from the substrate misorientation. Step bunching and large faceting along 〈01-10〉 and 〈10-10〉 directions occurred during the growth of GaN. Lowering the growth temperature suppresses large faceting, and results in reduction of the peak-to-valley height to 3 nm. However, the surface still has the same undulating features on a smaller length scale. On the other hand such morphology was not observed for GaN grown on (0001) on-axis SiC substrates (misorientation < 0.3o). The influence of the polytype of the SiC substrate and the misorientation angle and direction are also discussed. © 2005 Materials Research Society.

Molecular beam epitaxy of GaN on lattice-matched ZrB<inf>2</inf> substrates using low-temperature GaN and AlN nucleation layers

Armitage R., Nishizono K., Suda J., Kimoto T.

Materials Research Society Symposium Proceedings Vol. 831 page： 477 - 482 2005.8

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

GaN epilayers have been grown by plasma-assisted molecular-beam epitaxy on ZrB2 substrates with close in-plane lattice match. Growth processes utilizing both low-temperature GaN (LT-GaN) and AlN nucleation layers were investigated. The x-ray ω-scan widths for the optimized LT-GaN nucleation process were 400 and 750 arcsec for symmetric and asymmetric reflections, respectively. When using LT-GaN nucleation layers, the chemical incompatibility of ZrB2 results in a high dislocation density despite the in-plane lattice match. The epilayer polarity was N-polar for LT-GaN nucleation layers under all conditions investigated. For AlN nucleation layers, Gapolar epilayers were obtained under suitable conditions (Al-rich, lower nucleation temperatures) for nominal AlN thickness as low as 1 nm. From RHEED analysis it appears that a psuedomorphic Al wetting layer forms on the ZrB2 surface, and that using AlN as the nucleation layer may offer promise for reducing the epilayer defect density. © 2005 Materials Research Society.

Design and Fabrication of RESURF MOSFETs on 4H-SiC(0001), (1120), and 6H-SiC(0001)

Kimoto T, Kosugi H, Suda J, Kanzaki Y, Matsunami H

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 52 ( 1 ) page： 112 - 117 2005.1

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

Design and fabrication of lateral SiC reduced surface field (RESURF) MOSFETs have been investigated. The doping concentration (dose) of the RESURF and lightly doped drain regions has been optimized to reduce the electric field crowding at the drain edge or in the gate oxide by using device simulation. The optimum oxidation condition depends on the polytype: N2O oxidation at 1300 °C seems to be suitable for 4H-SiC, and dry O2 oxidation at 1250 °C for 6H-SiC. The average inversion-channel mobility is 22, 78, and 68 cm2 /Vs for 4H-SiC(0001), (112̄0), and 6H-SiC(0001) MOSFETs, respectively. RESURF MOSFETs have been fabricated on 10-μm-thick p-type 4H-SiC(0001), (112̄0), and 6H-SiC(0001) epilayers with an acceptor concentration of 1 × 1016 cm-3. A 6H-SiC(0001) RESURF MOSFET with a 3-μm channel length exhibits a high breakdown voltage of 1620 V and an on-resistance of 234 mΩ · cm2. A 4H-SiC(112̄0) RESURF MOSFET shows the characteristics of 1230 V-138 mΩ · cm2. © 2005 IEEE.

DOI： 10.1109/TED.2004.841358

1200 V-class 4H-SiC RIESURF MOSFETs with low on-resistances

Kimoto T, Kawano H, Suda J

PROCEEDINGS OF THE 17TH INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES & ICS page： 279 - 282 2005

Molecular beam epitaxy of GaN on lattice-matched ZrB2 substrates using low-temperature GaN and AlN nucleation layers

Armitage R, Nishizono K, Suda J, Kimoto T

GaN, AIN, InN and Their Alloys Vol. 831 page： 477 - 482 2005

Short-Channel Effects in 4H-SiC MOSFETs

Noborio M, Kanzaki Y, Suda J, Kimoto T, Matsunami H

SILICON CARBIDE AND RELATED MATERIALS 2004 Vol. 483 page： 821 - 824 2005

Dose designing for high-voltage 4H-SiC RESURF MOSFETs - device simulation and fabrication

Kawano H, Kimoto T, Suda J, Matsunami H

SILICON CARBIDE AND RELATED MATERIALS 2004 Vol. 483 page： 809 - 812 2005

Dose designing for high-voltage 4H-SiC RESURF MOSFETs - Device simulation and fabrication

Kawano H., Kimoto T., Suda J., Matsunami H.

Materials Science Forum Vol. 483-485 page： 809 - 812 2005

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

Optimum dose designing for 4H-SiC (0001) two-zone RESURF MOSFETs is investigated by device simulation and fabrication. Simulated results suggest that negative charge at the SiC/SiO2 interface significantly influences breakdown voltage. Simulation has also showed that breakdown voltage strongly depends on LDD (Lightly-Doped Drain) dose. The dose dependencies of the breakdown voltage experimentally obtained are in good agreement with the device simulation. A RESURF MOSFET, processed by N2O oxidation, with an optimized dose blocks 1080V and has a low on-resistance of 79 mΩcm 2 at a gate oxide field of 3.0 MV/cm, which is the best 4H-SiC RESURF MOSFET ever reported.

DOI： 10.4028/0-87849-963-6.809

Short-channel effects in 4H-SiC MOSFETs

Noborio M., Kanzaki Y., Suda J., Kimoto T., Matsunami H.

Materials Science Forum Vol. 483-485 page： 821 - 824 2005

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

Short-channel effects in SiC MOSFETs have been investigated. Planar MOSFETs with various channel lengths have been fabricated on p-type 4H-SiC (0001), (000-1) and (11-20) faces. Short-channel effects such as punchthrough behavior, decrease of threshold voltage and deterioration of subthreshold characteristics are observed. Furthermore, the critical channel lengths below which short-channel effects occur are analyzed as a function of p-body doping and oxide thickness by using device simulation. The critical channel lengths in the fabricated SiC MOSFETs are in agreement with those obtained from the device simulation. The results are also in agreement with the empirical relationship for Si MOSFETs.

DOI： 10.4028/0-87849-963-6.821

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