Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Breakdown Characteristics of 15-kV-Class 4H-SiC PiN Diodes With Various Junction Termination Structures

Niwa Hiroki, Feng Gan, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 59 ( 10 ) page： 2748 - 2752 2012.10

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

15-kV-class 4H-SiC PiN diodes with various junction termination structures have been experimentally investigated. Employment of the space-modulated junction termination extension (SM-JTE) and the two-zone JTE have realized a breakdown voltage over 15 kV, corresponding to 93% of the parallel-plane breakdown voltage. The window of the implanted JTE dose to achieve the ultrahigh voltage has been enlarged, which indicates the robustness to the deviation of effective JTE dose. From the comparison of the experimental JTE-dose dependence of breakdown voltage with the numerical device simulation, a shift toward the heavier JTE-dose region was observed. To explain the phenomenon, effects of the charges at the SiO 2/SiC interface are discussed. © 2012 IEEE.

DOI： 10.1109/TED.2012.2210044

Carrier Recombination in n-Type 4H-SiC Epilayers with Long Carrier Lifetimes

Ichikawa Shuhei, Kawahara Koutarou, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS EXPRESS Vol. 5 ( 10 ) 2012.10

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

A longest carrier lifetime of 33.2 μs was achieved by eliminating the Z 1/2 center via thermal oxidation at 1400 °C for 48 h and subsequent surface passivation with a nitrided oxide on a 220-μm-thick n-type 4H-SiC epilayer. By deep-level elimination, photoluminescence (PL) in the infrared region (wavelength: 700-950 nm) was remarkably enhanced at locations of threading dislocations. A threading screw dislocation exhibited much stronger infrared PL than a threading edge dislocation. The present results indicate that carrier recombination at extended defects becomes pronounced through the elimination of the Z 1/2 center in the epilayers. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.101301

Over-700-nm Critical Thickness of AlN Grown on 6H-SiC(0001) by Molecular Beam Epitaxy

Okumura Hironori, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 5 ( 10 ) 2012.10

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

We report on the critical thickness of AlN on SiC(0001). AlN was directly grown on 6H-SiC(0001) at 650 °C by rf-plasma-assisted molecular beam epitaxy. The growth layer had a relatively low threading dislocation density of 4 × 10 8-4 × 10 9 cm -2. Although the critical thickness of AlN on SiC(0001) is estimated to be 3.5nm using a Matthews-Blakeslee model, the critical thickness in our experiment was over 700 nm. Low dislocation density, a layer-by-layer growth mode, and low growth temperature may contribute to such a large critical thickness. Sharp and intense free exciton emission was observed in low-temperature PL measurements of the AlN layer. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.105502

Enhancement and control of carrier lifetimes in p-type 4H-SiC epilayers

Hayashi T., Asano K., Suda J., Kimoto T.

JOURNAL OF APPLIED PHYSICS Vol. 112 ( 6 ) 2012.9

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

Enhancement and control of carrier lifetimes in p-type 4H-SiC have been investigated. In this study, thermal oxidation and carbon ion implantation methods, both of which are effective for lifetime enhancement in n-type SiC, were attempted on 147-μm thick p-type 4H-SiC epilayers. Effects of surface passivation on carrier lifetimes were also investigated. The carrier lifetimes in p-type SiC could be enhanced from 0.9 μs (as-grown) to 2.6 μs by either thermal oxidation or carbon implantation and subsequent Ar annealing, although the improvement effect for the p-type epilayers was smaller than that for the n-type epilayers. After the lifetime enhancement, electron irradiation was performed to control the carrier lifetime. The distribution of carrier lifetimes in each irradiated region was rather uniform, along with successful lifetime control in the p-type epilayer in the range from 0.1 to 1.6 μs. © 2012 American Institute of Physics.

DOI： 10.1063/1.4748315

4H-SiC pn Photodiodes with Temperature-Independent Photoresponse up to 300 degrees C

Watanabe Naoki, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 5 ( 9 ) 2012.9

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

4H-SiC pn photodiodes were fabricated and the temperature dependence of the photoresponse was measured for various wavelengths (280-365 nm) as a function of reverse-bias voltage. A temperature-independent photoresponse was obtained at 280nm illumination from room temperature to 300 °C under zero-bias condition. By applying reverse-bias voltage up to 150 V, the wavelength of the temperature-independent photoresponse was varied from 280 to 300 nm. The temperature-independent photoresponse was explained by the temperature dependence of optical absorption coefficient together with surface recombination effect. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.094101

Breakdown characteristics of 12-20 kV-class 4H-SiC PiN diodes with improved junction termination structures

Niwa H., Feng G., Suda J., Kimoto T.

Proceedings of the International Symposium on Power Semiconductor Devices and ICs page： 381 - 384 2012.8

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

Ultrahigh-voltage 4H-SiC PiN diodes with improved junction termination extension (JTE) structures have been investigated. Breakdown characteristics of 4H-SiC PiN diodes with conventional single-zone JTE was shown to be severely affected by the charge near the SiO 2/SiC interface from experiment and device simulation. Taking the effect of the interface charge into account, and by using "Space-Modulated" JTE structure with a wide optimum JTE-dose window to tolerate the impact of interface charge, we achieved a breakdown voltage of 21.7 kV (81 % of the ideal breakdown voltage calculated from the epilayer structure), which is the highest breakdown voltage among any semiconductor devices ever reported. © 2012 IEEE.

DOI： 10.1109/ISPSD.2012.6229101

Fundamental study on junction termination structures for ultrahigh-voltage SiC PiN diodes

Niwa H., Suda J., Kimoto T.

IMFEDK 2012 - 2012 International Meeting for Future of Electron Devices, Kansai page： 56 - 57 2012.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IMFEDK 2012 - 2012 International Meeting for Future of Electron Devices, Kansai

15 kV-class 4H-SiC PiN diodes with various junction termination extension (JTE) structures have been experimentally investigated. JTE-dose dependence of the breakdown voltage for conventional single and two-zone JTE showed a narrow window of optimum JTE-dose to obtain high breakdown voltage. To widen this window, space-modulated JTE (SM-JTE) was introduced. 4H-SiC PiN diodes with SM-JTE showed a highest breakdown voltage of 15 kV, and a widening of the optimum JTE-dose window to obtain ultrahigh-voltage was realized at the same time. © 2012 IEEE.

DOI： 10.1109/IMFEDK.2012.6218579

21.7 kV 4H-SiC PiN Diode with a Space-Modulated Junction Termination Extension

Niwa Hiroki, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS EXPRESS Vol. 5 ( 6 ) 2012.6

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

Ultrahigh-voltage 4H-SiC mesa PiN diodes are fabricated and characterized. An original space-modulated two-zone junction termination extension (SM-two-zone JTE) has realized a laterally tapered profile of the JTE dose, which enlarged the tolerance to the deviation of effective JTE dose compared with a conventional two-zone JTE. We demonstrate a SiC PiN diode with a breakdown voltage of 21.7 kV (81% of the ideal breakdown voltage calculated from the epilayer structure), which is the highest breakdown voltage among any semiconductor devices ever reported. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.064001

Lattice mismatch and crystallographic tilt induced by high-dose ion-implantation into 4H-SiC

Sasaki S., Suda J., Kimoto T.

JOURNAL OF APPLIED PHYSICS Vol. 111 ( 10 ) 2012.5

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

Lattice parameters of high-dose ion-implanted 4H-SiC were investigated with reciprocal space mapping (RSM). N, P, Al, or (CSi) ions were implanted into lightly doped epilayers to form a (330-520) nm-deep box profile with concentrations of 10 19-10 20 atoms/cm 3. After activation annealing at 1800 °C, RSM measurements were conducted. The RSM images for (0008) reflection revealed that high-dose ion implantation causes c-lattice expansion in implanted layers, irrespective of ion species. In addition, crystallographic tilt was observed after high-dose ion implantation. The tilt direction is the same for all the samples investigated; the c-axis of the implanted layers is inclined toward the ascending direction of the off-cut. The c-lattice mismatch and the tilt angle increased as the implantation dose increases, indicating that the implantation damage is responsible for the lattice parameter change. From these results and transmission electron microscopy observation, the authors conclude that the c-lattice mismatch and the crystallographic tilt are mainly caused by secondary defects formed after the ion-implantation and activation-annealing process. © 2012 American Institute of Physics.

DOI： 10.1063/1.4720435

AlN/GaN Short-Period Superlattice Coherently Grown on 6H-SiC(0001) Substrates by Molecular Beam Epitaxy

Kikuchi Ryosuke, Okumura Hironori, Kaneko Mitsuaki, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 5 ( 5 ) 2012.5

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

We demonstrate the coherent growth of AIN/GaN short-period superlattice (SPSL) on 6H-SiC(0001) substrates by molecular beam epitaxy. A high-quality 5-nm-thick AIN layer was grown on SiC as a template layer, followed by the growth of AIN (12BL)/GaN (2BL) SPSL, which consists of 40 periods (total thickness: 140nm). The SPSL was coherently grown on SiC, and its threading dislocation density (TDD) was as low as 8 × 10 8cm -2. The SPSL, which had 3-BL-thick GaN layers, was relaxed, and the TDD increased to 8 × 10 10cm -2. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.5.051002

Current Transport Characteristics of Quasi-AlxGa1-xN/SiC Heterojunction Bipolar Transistors with Various Band Discontinuities

Okuda Takafumi, Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 51 ( 4 ) 2012.4

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

The current transport characteristics of quasi-Al xGa 1-xN/SiC heterojunction bipolar transistors (HBTs) with various band discontinuities were investigated in a low-current range using a Gummel plot. In the low-current range, the base currents of the HBTs were dominated by recombination currents. The collector current characteristics of the HBTs in the low-current range were almost the same in spite of the various band discontinuities, and the ideality factor n was 1.0. The band discontinuities at the heterojunction had no effect on electron injection in the lowcurrent range. This is because the collector currents were dominated by diffusion process in the base region rather than by injection process at the AlGaN/SiC interface. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.04DP09

Analytical model for reduction of deep levels in SiC by thermal oxidation

Kawahara Koutarou, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 111 ( 5 ) 2012.3

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

Two trap-reduction processes, thermal oxidation and C + implantation followed by Ar annealing, have been discovered, being effective ways for reducing the Z 12 center (E C - 0.67 eV), which is a lifetime killer in n-type 4H-SiC. In this study, it is shown that new deep levels are generated by the trap-reduction processes in parallel with the reduction of the Z 12 center. A comparison of defect behaviors (reduction, generation, and change of the depth profile) for the two trap-reduction processes shows that the reduction of deep levels by thermal oxidation can be explained by an interstitial diffusion model. Prediction of the defect distributions after oxidation was achieved by a numerical calculation based on a diffusion equation, in which interstitials generated at the SiO 2SiC interface diffuse to the SiC bulk and occupy vacancies related to the origin of the Z 12 center. The prediction based on the proposed analytical model is mostly valid for SiC after oxidation at any temperature, for any oxidation time, and any initial Z 12-concentration. Based on the results, the authors experimentally achieved the elimination of the Z 12 center to a depth of about 90 μm in the sample with a relatively high initial-Z 12-concentration of 10 13 cm -3 by thermal oxidation at 1400°C for 16.5 h. Furthermore, prediction of carrier lifetimes in SiC from the Z 12 profiles was realized through calculation based on a diffusion equation, which considers excited-carrier diffusion and recombination in the epilayer, in the substrate, and at the surface. © 2012 American Institute of Physics.

DOI： 10.1063/1.3692766

High temperature annealing of n-type 4H-SiC: Impact on intrinsic defects and carrier lifetime

Zippelius Bernd, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 111 ( 3 ) 2012.2

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

In this paper, the impact of high-temperature annealing of 4H silicon carbide (SiC) on the formation of intrinsic defects, such as Z 1/2 and EH 6/7, and on carrier lifetimes was studied. Four nitrogen-doped epitaxial layers with various initial concentrations of the Z 1/2- and EH 6/7-centers (10 11 - 10 14 cm -3) were investigated by means of deep level transient spectroscopy and microwave photoconductance decay. It turned out that the high-temperature annealing leads to a monotone increase of the Z 1/2- and EH 6/7- concentration starting at temperatures between 1600°C and 1750°C, depending on the initial defect concentration. In the case of samples with high initial defect concentration (10 14 cm -3) a distinct decrease in Z 1/2- and EH 6/7-concentration in the temperature range from 1600°C to 1750°C was observed, being consistent with previous reports. For higher annealing temperatures (T anneal 1750°C), the defect concentration is independent of the samples' initial values. As a consequence, beside the growth conditions, such as C/Si ratio, the thermal post-growth processing has a severe impact on carrier lifetimes, which are strongly reduced for samples annealed at high temperatures. © 2012 American Institute of Physics.

DOI： 10.1063/1.3681806

Growth of Nitrogen-Polar 2H-AlN on Step-Height-Controlled 6H-SiC(000(1)over-bar) Substrate by Molecular-Beam Epitaxy

Okumura Hironori, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 51 ( 2 ) 2012.2

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

200-nm-thick N-polar AlN layers were grown on 6H-SiC(0001̄) substrates with 6-bilayer-high steps by molecular-beam epitaxy. During N-polar AlN growth, multinucleation growth occured easily, increasing the surface roughness of AlN. By reducing supersaturation (nucleation probability), the surface roughness was improved. The FWHMs of (0002) and (011̄2̄) ω-scan diffraction peaks of the AlN layer were 120 and 210 arcsec, respectively. The formation of stacking-mismatch boundaries (SMBs) was successfully suppressed by step-height control of the SiC substrate and the initial layer-by-layer growth. Most of the threading dislocations (TDs) were generated at the step edges of the SiC surfaces. The density of TDs in the AlN layers was 2 × 10 9 cm -2. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.02BH02

Space-Modulated Junction Termination Extension for Ultrahigh-Voltage p-i-n Diodes in 4H-SiC

Feng Gan, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 59 ( 2 ) page： 414 - 418 2012.2

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

An edge termination method, referred to as space-modulated junction termination extension (SMJTE) combined with a mesa structure, is presented for ultrahigh-voltage p-i-n diodes in 4H-SiC. Numerical device simulations have been performed for over 15-kV-class 4H-SiC p-i-n diodes with the proposed edge termination. The structure exhibits a high breakdown capability with an improved tolerance for the deviation of impurity dose in the JTE region. Unlike conventional multi-implantation, the proposed termination technique utilizes a single-step implantation with a single mask. A desired laterally tapered doping profile is achieved by fragmenting a conventional JTE region using relatively wide spaces. The simple process of the proposed edge termination makes it applicable to fabrication of various high-voltage devices in 4H-SiC. © 2006 IEEE.

DOI： 10.1109/TED.2011.2175486

Breakdown Characteristics of 12-20 kV-class 4H-SiC PiN Diodes with Improved Junction Termination Structures

Niwa Hiroki, Feng Gan, Suda Jun, Kimoto Tsunenobu

2012 24TH INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND ICS (ISPSD) page： 381 - 384 2012

Elimination of Deep Levels in Thick SiC Epilayers by Thermal Oxidation and Proposal of the Analytical Model

Kawahara Koutarou, Suda Jun, Kimoto Tsunenobu

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 Vol. 717-720 page： 241 - 246 2012

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

It has been clarified that the Z1/2 center, a well known deep level as a lifetime killer, can be reduced to the concentration below 10 11 cm-3 by thermal oxidation or C+ implantation plus Ar annealing. In this study, the authors investigate the trap-reduction phenomena systematically (experimentally), and propose a model to analyze the phenomena. Furthermore, prediction of the defect distributions is realized by solving a diffusion equation in accordance with the trap reduction model. This analytical model can explain almost all experimental data: oxidation-temperature dependence, oxidation-time dependence, and initial-Z1/2- concentration dependence of the defect reduction. Based on these results, the authors achieved the elimination of the Z1/2 center to a depth of ∼100 μm in a sample with a relatively high initial-Z1/2- concentration of 1013 cm-3 by thermal oxidation at 1400°C for 16.5 h. © (2012) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.717-720.241

Doping-Induced Lattice Mismatch and Misorientation in 4H-SiC Crystals

Sasaki S., Suda J., Kimoto T.

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 Vol. 717-720 page： 481 - 484 2012

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

The c- and a-lattice constants of nitrogen-doped 4H-SiC were measured in the wide temperature range (RT - 1100°C). The samples used in this study were heavily doped substrates and lightly-doped free-standing epilayers. The lattice constants at room temperature are almost identical for all the samples. However, the lattice contraction by heavy nitrogen doping was clearly observed at high temperatures, which indicates that the thermal expansion coefficients are dependent on the nitrogen concentration. The lattice mismatch (Δd/d) between a lightly-doped free-standing epilayer (Nd = 6×10 14 cm-3) and a heavily-doped substrate (Nd = 2×1019 cm-3) was calculated as 1.7×10 -4 at 1100°C. The authors also investigated lattice constants of high-dose N+, P+, and Al+-implanted 4H-SiC. Reciprocal space mapping (RSM) was utilized to investigate the lattice mismatch and misorientation. The RSM images show the c-lattice expansion and c-axis tilt of the ion-implanted layers, irrespective of ion species. The authors conclude that the lattice expansion is not caused by heavy doping itself, but by secondary defects formed after the ion-implantation and activation-annealing process. © (2012) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.717-720.481

Defect Electronics in SiC and Fabrication of Ultrahigh-Voltage Bipolar Devices

Kimoto T., Suda J., Feng G., Miyake H., Kawahara K., Niwa H., Okuda T., Ichikawa S., Nishi Y.

GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 2 Vol. 50 ( 3 ) page： 25 - 35 2012

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ECS Transactions

Fast epitaxial growth, defect reduction, device designing, and process development in SiC toward ultrahigh-voltage (> 10 kV) bipolar devices are investigated. 100∼200μ-thick 4H-SiC epilayers with a low background doping concentration in the low 1013 cm-3 can be grown at a growth rate greater than 50μ/h. Impacts of extended defects on carrier recombination are clarified in photoluminescence mapping measurements. Generation and reduction of Z1/2 center, the dominant lifetime killer, are summarized. After Z1/2 elimination by thermal oxidation at 1400°C, the carrier lifetime can be enhanced to 25 s or even longer. By utilizing space-modulated junction termination extension, a 21.7 kV PiN diode is demonstrated. Through unique process development, the current gain in bipolar junction transistors is increased to 250∼330. © The Electrochemical Society.

DOI： 10.1149/05003.0025ecst

Enhanced Current Gain (> 250) in 4H-SiC Bipolar Junction Transistors by A Deep-Level-Reduction Process

Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 Vol. 717-720 page： 1117 - 1122 2012

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

We demonstrate 4H-SiC bipolar junction transistors (BJTs) with an enhanced current gain over 250. High current gain was achieved by utilizing optimized device geometry as well as optimized surface passivation, continuous epitaxial growth of the emitter-base junction, combined with an intentional deep-level-reduction process based on thermal oxidation to improve the lifetime in p-SiC base. We achieved a maximum current gain (β) of 257 at room temperature and 127 at 250°C for 4H-SiC BJTs fabricated on the (0001)Si-face. The gain of 257 is twice as large as the previous record gain. We also demonstrate BJTs on the (000-1)C-face that showed the highest β of 439 among the SiC BJTs ever reported. © (2012) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.717-720.1117

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