Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Ion Implantation Technology in SiC for High-Voltage/High-Temperature Devices

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

2016 16TH INTERNATIONAL WORKSHOP ON JUNCTION TECHNOLOGY (IWJT) page： 54 - 58 2016

Orientation and size effects on phonon-limited hole mobility in rectangular cross-sectional germanium nanowires

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

2014 Silicon Nanoelectronics Workshop, SNW 2014 2015.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2014 Silicon Nanoelectronics Workshop, SNW 2014

The phonon-limited hole mobility in rectangular cross-sectional [001], [110], [111], and [112]-oriented germanium nanowires was calculated and the hole transport characteristics were compared. The calculation revealed that [110] germanium nanowires with larger height along [001] show high hole mobility and are favorable for p-channel FETs.

DOI： 10.1109/SNW.2014.7348616

Oxidation-induced majority and minority carrier traps in n- and p-type 4H-SiC

Okuda Takafumi, Alfieri Giovanni, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 8 ( 11 ) 2015.11

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

We investigated majority and minority carrier traps in lightly doped n-and p-type 4H-SiC epitaxial layers before and after thermal oxidation using deep level transient spectroscopy and minority carrier transient spectroscopy. We detected oxidation-induced new minority carrier traps, HO1 (EV + 0.36 eV) and HO2 (EV + 0.54 eV) for n-type 4H-SiC, and EO1 (EC % 0.59 eV) and EO2 (EC % 0.84 eV) for p-type 4H-SiC after thermal oxidation at 1300 °C. After subsequent Ar annealing at 1550 °C, the HO1, HO2, and EO1 centers disappeared, whereas the concentration of the EO2 center increased. The properties of these carrier traps are discussed.

DOI： 10.7567/APEX.8.111301

Impact Ionization Coefficients in 4H-SiC Toward Ultrahigh-Voltage Power Devices

Niwa Hiroki, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 62 ( 10 ) page： 3326 - 3333 2015.10

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

A temperature dependence of impact ionization coefficients in 4H-SiC was studied in a wide range of electric field toward the accurate designing of ultrahigh-voltage devices. The photomultiplication measurement was conducted for various photodiodes with different multiplication layer structures to obtain multiplication factors and ionization coefficients in a wide range of electric field strength. Especially, using multiplication layer structure with low doping concentration, the hole impact ionization coefficient was extracted at low electric field of 1 MV/cm. In high-temperature measurement, the hole ionization coefficient decreased with the increase of temperature, as observed in other semiconductor materials. For the electron ionization coefficient, however, its temperature dependence was very small and values obtained at room temperature could be used, at least up to 150 °C.

DOI： 10.1109/TED.2015.2466445

Impacts of surface roughness scattering on hole mobility in germanium nanowires

Tanaka H., Suda J., Kimoto T.

2015 Silicon Nanoelectronics Workshop, SNW 2015 2015.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2015 Silicon Nanoelectronics Workshop, SNW 2015

The hole mobility in rectangular cross-sectional germanium nanowires was calculated taking into account phonon and surface roughness scattering (SRS). SRS was modeled based on atomistic description of electronic states, and the impacts of SRS on hole mobility were analyzed.

Temperature dependence of forward characteristics for ultrahigh-voltage SiC p-i-n diodes with a long carrier lifetime

Kaji Naoki, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 54 ( 9 ) 2015.9

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

Forward characteristics of ultrahigh-voltage 4H-SiC p-i-n diodes having four different n--layer (i-layer) thicknesses from 48 to 198μm were investigated in the temperature range from room temperature to 573 K. After enhancement of carrier lifetimes in i-layers, nearly ideal forward characteristics (differential on-resistance = 1.1-5.5mΩcm2 at 100A/cm2) were obtained at room temperature. The forward voltage drop decreased with temperature, which is consistent with the temperature dependence of junction voltage. The differential on-resistance exhibited a slight increase at elevated temperatures, which can mainly be ascribed to the increase in substrate resistance.

DOI： 10.7567/JJAP.54.098004

Impacts of orientation and cross-sectional shape on hole mobility of Si nanowire MOSFETs

Fujihara H., Morioka N., Tanaka H., Suda J., Kimoto T.

IMFEDK 2015 - 2015 International Meeting for Future of Electron Devices, Kansai page： 106 - 107 2015.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IMFEDK 2015 - 2015 International Meeting for Future of Electron Devices, Kansai

We fabricated 〈100〉, 〈110〉, 〈111〉, and 〈112〉 p-channel gate-all-around Si nanowire (SiNW) MOSFETs, cross sections of which are rectangles with various widths, and investigated the hole mobility of the SiNW MOSFETs using the double Lm method. Measured hole mobilities of SiNW MOSFETs were about 80-140 cm2/Vs at surface carrier density of 1 × 1013 cm-2. The dependences of the hole mobility on orientations and cross-sectional shapes of nanowires were analyzed. The orientation and geometry dependences can be explained by the band structures calculated by tight-binding approximation.

DOI： 10.1109/IMFEDK.2015.7158572

インタビュー：手作りのGaN pn接合型青色／紫外LEDに通電したときの発光は，目に沁(し)みる本当に鮮やかなコバルトブルーの光でした

赤﨑勇, 西永頌, 榊裕之, 須田淳, 岩谷素顕

応用物理 Vol. 84 ( 6 ) page： 492 - 504 2015.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：公益社団法人応用物理学会

<p>1949年，赤﨑先生が京都大学に在学中，湯川秀樹先生がノーベル物理学賞を受賞されました．若き赤﨑先生は「湯川先生のお仕事というのは雲の上のことだけれど，自分も何か小さいことでもいいから，今までにない何かをやりたい」と強く思ったそうです．そして，17年後の1966年，松下電器東京研究所の室長としてGaAsP系赤色LEDの開発を進めていた赤﨑先生は，「青がない」ことに気が付きます．それを実現することこそが「何か」だと確信し，窒化物の研究を始められました．その後，20年間におよぶ地道な研究を経て，1986年，ついに低温バッファ層を用いて高品質GaNの結晶成長に成功し，次いで1989年，GaN pn接合型青色／紫外LEDの作製を実現．今日のGaN光・電子デバイスの基盤が確立されることとなりました．赤﨑先生にノーベル賞受賞発表後の様子から，若い頃の思い出，研究の苦労と喜び，応用物理学会や若手会員へのメッセージを伺いました．</p>

DOI： 10.11470/oubutsu.84.6_492

Temperature dependence of current gain in 4H-SiC bipolar junction transistors

Asada Satoshi, Okuda Takafumi, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 54 ( 4 ) 2015.4

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

The temperature dependence of current gain from 140 to 460K in 4H-SiC bipolar junction transistors (SiC BJTs) was investigated. The current gain increased from 110 to 1200 with decreasing temperature from 460 to 200 K. The high current gain at the low temperature can be ascribed to the enhanced incomplete ionization of aluminum acceptors in the base layer, resulting in the increase in injection efficiency. However, when the temperature was further reduced from 200 to 140 K, the current gain decreased from 1200 to 515, which is caused by high injection condition in the base layer, because of a very low hole concentration below 200 K.

DOI： 10.7567/JJAP.54.04DP13

Progress in ultrahigh-voltage SiC devices for future power infrastructure

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

Technical Digest - International Electron Devices Meeting, IEDM Vol. 2015-February ( February ) page： 2.5.1 - 2.5.4 2015.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Technical Digest - International Electron Devices Meeting, IEDM

UHV (> 15 kV) SiC PiN diodes and IGBTs with improved on-state performance are presented. Through enhancement of carrier lifetime and optimization of junction termination, a breakdown voltage over 26.9 kV and a differential on-resistance of 9.7 mΩcm2 were achieved for PiN diodes. Flip-type n-channel IGBTs with a chip size of 8 mm × 8 mm exhibited a breakdown voltage over 16 kV, and 6.5 kV - 60 A switching at 250°C was demonstrated.

DOI： 10.1109/IEDM.2014.7046967

Interface Properties of 4H-SiC (11(2)over-bar0) and (1(1)over-bar00) MOS Structures Annealed in NO

Nakazawa Seiya, Okuda Takafumi, Suda Jun, Nakamura Takashi, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 62 ( 2 ) page： 309 - 315 2015.2

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

Interface properties of 4H-SiC (1120) and (1100) metal-oxide-semiconductor (MOS) structures annealed in nitric oxide are characterized by conductance, high-low, and C-Ψs methods. Compared with 4H-SiC (0001) MOS structures, generation of very fast interface states by nitridation is much smaller in 4H-SiC (1120) and (1100). The effective mobility of planar MOSFETs fabricated on Al+-implanted p-body doped to 1×1017 cm-3 is 103 cm2/Vs on (1100), 92 cm2/Vs on (1120), and 20 cm2/Vs on (0001). The mobility-limiting factors are discussed on the basis of experimental results. The high channel mobilities for (1120) and (1100) MOSFETs can be correlated with the lower density of fast interface states generated by nitridation.

DOI： 10.1109/TED.2014.2352117

Ultrahigh- Voltage SiC p-i-n Diodes With Improved Forward Characteristics

Kaji Naoki, Niwa Hiroki, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 62 ( 2 ) page： 374 - 381 2015.2

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

Silicon carbide (SiC) p-i-n diodes having five different n--layer ( i-layer) thicknesses from 48 to 268 μm are fabricated. The forward characteristics of SiC p-i-n diodes are significantly improved by carrier-lifetime enhancement. After this improvement, the differential on-resistance is inversely proportional to the square root of current density for all the diodes with different thicknesses of n--layer. As a result, the forward current density-voltage characteristics can be approximately expressed by a parabolic function, as in the case of Si p-i-n diodes. Using a 268- μm-thick n--layer, the lifetime enhancement, and an improved space-modulated junction termination extension structure, a very high blocking voltage over 26.9 kV and low differential on-resistance of 9.7 mΩ·cm2 are achieved.

DOI： 10.1109/TED.2014.2352279

High-temperature operation of electrostatically-excited single-crystalline 4H-SiC microcantilever resonators

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

Materials Science Forum Vol. 821-823 page： 914 - 918 2015

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

We fabricated electrostatically-excited single-crystalline 4H-SiC microcantilever resonators with various thicknesses and lengths. Their resonant characteristics were investigated from room temperature (RT) up to 600°C. The resonant frequency of the cantilevers decreased with increasing temperature. From the results, the temperature dependence of Young’s modulus of single-crystalline 4H-SiC was obtained, i.e., 3% decrement with increasing temperature from RT to 600°C. The cantilevers with different thicknesses showed different temperature dependences of the quality factor. A 2-μm-thick cantilever exhibited a high quality factor (Q) (250,000) at RT and the Q decreased to 6,000 at 600°C, which can be explained by thermoelastic damping. On the other hand, a Q of a 0.45-μm-thick cantilever was still high (50,000) even at 600°C.

DOI： 10.4028/www.scientific.net/MSF.821-823.914

Impacts of Surface Roughness Scattering on Hole Mobility in Germanium Nanowires

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

2015 SILICON NANOELECTRONICS WORKSHOP (SNW) 2015

Impacts of Orientation and Cross-sectional Shape on Hole Mobility of Si Nanowire MOSFETs

Fujihara Hiroaki, Morioka Naoya, Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

2015 IEEE INTERNATIONAL MEETING FOR FUTURE OF ELECTRON DEVICES, KANSAI (IMFEDK) 2015

Influence of conduction-type on thermal oxidation rate in SiC(0001) with various doping densities

Kobayashi T., Suda J., Kimoto T.

Materials Science Forum Vol. 821-823 page： 456 - 459 2015

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

It was discovered that the oxidation rate for SiC depended on the conduction type. The oxidation was performed for SiC(0001) with nitrogen doping (n-type) in the range from 2×1016 cm-3 to 1×1019 cm-3, and aluminum doping (p-type) in the range from 2×1015 cm-3 to 1×1019 cm-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.

DOI： 10.4028/www.scientific.net/MSF.821-823.456

Geometrical and band-structure effects on phonon-limited hole mobility in rectangular cross-sectional germanium nanowires

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

JOURNAL OF APPLIED PHYSICS Vol. 116 ( 23 ) 2014.12

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

We calculated the phonon-limited hole mobility in rectangular cross-sectional [001], [110], [111], and [112]-oriented germanium nanowires, and the hole transport characteristics were investigated. A tight-binding approximation was used for holes, and phonons were described by a valence force field model. Then, scattering probability of holes by phonons was calculated taking account of hole-phonon interaction atomistically, and the linearized Boltzmann's transport equation was solved to calculate the hole mobility at low longitudinal field. The dependence of the hole mobility on nanowire geometry was analyzed in terms of the valence band structure of germanium nanowires, and it was found that the dependence was qualitatively reproduced by considering an average effective mass and the density of states of holes. The calculation revealed that [110] germanium nanowires with large height along the [001] direction show high hole mobility. Germanium nanowires with this geometry are also expected to exhibit high electron mobility in our previous work, and thus they are promising for complementary metal-oxide-semiconductor (CMOS) applications.

DOI： 10.1063/1.4904844

Impact of conduction type and doping density on thermal oxidation rate of SiC(0001)

Kobayashi Takuma, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS EXPRESS Vol. 7 ( 12 ) 2014.12

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

We discovered that the oxidation rate of SiC depends on the conduction type. The oxidation was faster in n-type SiC than in p-type SiC. The linear rate constant B/A was higher for n-type SiC than for p-type SiC, which may be caused by the stability of Si vacancies. The parabolic rate constant B was nearly constant for n-type SiC, whereas it decreased dramatically for heavily doped p-type SiC. Secondary-ion mass spectrometry measurements revealed that a high density of Al atoms was incorporated in the oxide of p-type SiC, which may hinder the diffusion of O2 or COx.

DOI： 10.7567/APEX.7.121301

Decay curve analyses in carrier lifetime measurements of p- and n-type 4H-SiC epilayers

Hayashi Toshihiko, Okuda Takafumi, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 53 ( 11 ) 2014.11

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

The impacts of the ambipolar diffusion constant and surface recombination in carrier lifetime measurements of p- and n-type 4H-SiC epilayers are investigated in detail by comparing a numerical simulation based on a diffusion equation and the measurement of microwave photoconductance decay (μ-PCD) curves measured from 4H-SiC epilayers. The simulation reveals that the shapes of decay curves of excess carrier concentration in epilayers, which defines the effective carrier lifetime, are different between p- and n-type 4H-SiC under a low-level injection condition, even when the bulk lifetime and the surface recombination velocity are fixed to the same values for p- and n-type epilayers. In experiments, the shapes of the microwave photoconductance decay curves measured from p- and n-type 4H-SiC epilayers show a similar tendency to the simulation results under a low-level injection condition. This is attributed to the difference in the dependence of the ambipolar diffusion constant on the excess carrier concentration for p- and n-type 4H-SiC. The comparison of μ-PCD decay curves obtained from 50-μm-thick epilayers with different surface passivation indicates that the surface recombination velocity on the epilayer passivated with deposited SiO2 followed by NO annealing is about one order of magnitude lower than that of the epilayer passivated with the dry oxide.

DOI： 10.7567/JJAP.53.111301

Temperature dependence of optical absorption coefficient of 4H-and 6H-SiC from room temperature to 300 degrees C

Watanabe Naoki, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 53 ( 10 ) 2014.10

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

Optical absorption coefficients of 4H- and 6H-SiC were measured at cutoff wavelengths from a value of 0 to 400-500cm-1 at various temperatures that is from room temperature to 300 °C. The redshift of the absorption edge with increasing temperature was observed. It is caused by a decrease in bandgap energy and a change in phonon occupation with increasing temperature. By considering TA-, LA-, and TO-mode phonon-assisted indirect transitions, the measured data are well fitted using a theoretical model. The obtained parameters are reported.

DOI： 10.7567/JJAP.53.108003

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