Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Effect of Postoxidation Nitridation on Forward Current-Voltage Characteristics in 4H-SiC Mesa p-n Diodes Passivated With SiO2

Asada Satoshi, Kimoto Tsunenobu, Suda Jun

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 64 ( 7 ) page： 3016 - 3018 2017.7

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

An origin of shunt current, a ledge in forward current-voltage ( ${I}$ - ${V}$ ) characteristics, in 4H-SiC mesa p-n diodes was investigated by adopting various surface passivation processes. Experimental results indicated that the shunt current path is located along the mesa sidewall and the shunt current is enlarged with increasing NO-annealing period and temperature. Based on these results, we qualitatively explain that nitrogen-related positive charges near the SiC/SiO2 interface, which are formed by postoxidation nitridation, induce band bending and lowering of the diffusion potential along the mesa sidewall, resulting in occurrence of the shunt current.

DOI： 10.1109/TED.2017.2700336

Electrical properties of n- and p-type 4H-SiC formed by ion implantation into high-purity semi-insulating substrates

Fujihara Hiroaki, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 56 ( 7 ) 2017.7

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

Phosphorus or aluminum ions were directly implanted into semi-insulating 4H-SiC substrates with no epitaxial layers to form n- or p-type layers, respectively, with doping densities in the range from 1017 to 1019 cm-3. The electrical properties of these implanted layers annealed at 1650°C were characterized by Hall effect measurements in the temperature range of 160-900K. The electrical activation ratios of implanted dopants were 88-98%. The density of compensating defects was higher in Al+-implanted layers than in P+-implanted ones. The mobilities of the implanted layers were mostly comparable to those of epitaxial layers in the doping range investigated.

DOI： 10.7567/JJAP.56.070306

Design Criterion for SiC BJTs to Avoid ON-Characteristics Degradation Due to Base Spreading Resistance

Asada Satoshi, Kimoto Tsunenobu, Suda Jun

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 64 ( 5 ) page： 2086 - 2091 2017.5

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

It is empirically known that the ON-resistance (voltage) of the SiC bipolar junction transistors (BJTs) with a thin-base layer is prone to be larger than the resistance of a voltage-blocking collector layer. In this paper, we explain the mechanism of this degradation of ON-characteristics by focusing on a high base spreading resistance and a parasitic diode existing below the base contact. An equivalent circuit model of the SiC BJT was proposed, and SPICE simulation was performed.In addition, TCAD simulation confirmed the validity of the model well. Based on the model, a design criterion to avoid the unwanted increase of the ON-resistance is proposed.

DOI： 10.1109/TED.2017.2684181

Temperature dependence of barrier height in Ni/n-GaN Schottky barrier diode

Maeda Takuya, Okada Masaya, Ueno Masaki, Yamamoto Yoshiyuki, Kimoto Tsunenobu, Horita Masahiro, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 10 ( 5 ) 2017.5

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

The temperature dependence of barrier height in a Ni/n-GaN Schottky barrier diode fabricated on a GaN homoepitaxial layer was investigated by capacitance-voltage, current-voltage, and internal photoemission measurements in the range of 223-573 K. The barrier height obtained by these methods linearly decreased with increasing temperature. The temperature coefficient was %(1.7-2.3) ' 10-4 eV/K, which is about half of the temperature coefficient of the band gap reported previously. This indicates that the decrease in the barrier height may mainly reflect the shrinkage of the band gap (lowering of the conduction band edge) in GaN with increasing temperature.

DOI： 10.7567/APEX.10.051002

Interface properties of NO-annealed 4H-SiC (0001), (11(2)over-bar0), and (1(1)over-bar00) MOS structures with heavily doped p-bodies

Kobayashi Takuma, Nakazawa Seiya, Okuda Takafumi, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 121 ( 14 ) 2017.4

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

We investigated electrical characteristics of nitric oxide (NO)-annealed silicon carbide (SiC) (0001 ), (11 2 ¯ 0 ), and (1 1 ¯ 00 ) metal-oxide-semiconductor field effect transistors (MOSFETs) with heavily doped p-bodies (NA = 1 × 1017-3 × 1018 cm−3). Regardless of crystal faces or off-direction, the channel mobility decreased for higher acceptor density. We evaluated the interface state density (Dit) very near the bottom edge of 2-dimensional density of states (2D-DOS) in the conduction band of SiC from the low-temperature subthreshold slope of the MOSFETs. When the acceptor density of the p-body of the MOSFET is increased, the energy levels of 2D-DOS increase due to a stronger quantum confinement effect. Accordingly, the carriers in the heavily doped channel are influenced by the interface states located at higher energy levels. In the SiC MOS structures, the Dit values significantly increase near the conduction band edge (EC). Thus, MOSFETs on heavily doped p-bodies are affected by the higher density of Dit, leading to substantially lower mobility.

DOI： 10.1063/1.4981127

Reduction of interface state density in SiC (0001) MOS structures by post-oxidation Ar annealing at high temperature

Kobayashi Takuma, Suda Jun, Kimoto Tsunenobu

AIP ADVANCES Vol. 7 ( 4 ) 2017.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AIP Advances

We found that post-oxidation Ar annealing at high temperature is effective in reducing the interface state density (Dit) near the conduction band edge (EC) of SiC (0001) MOS structures. The Dit reduction effect is comparable to that of nitridation process (annealing in nitric oxide (NO)) which has been a standard in SiC MOS technologies, without introducing any foreign atoms into the interface/oxide. The generation of fast interface states, which have been pointed out as a problem of nitridation process, is suppressed in the case of Ar annealing. In the proposed method, the final Dit values are mainly determined by the Ar annealing temperature rather than the initial oxidation temperature. The Dit values are not sensitive to the cooling speed, which means that rapid cooling is not necessary in the proposed method.

DOI： 10.1063/1.4980024

Ultrahigh-Voltage SiC MPS Diodes With Hybrid Unipolar/Bipolar Operation

Niwa Hiroki, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 64 ( 3 ) page： 874 - 881 2017.3

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

In this paper, ultrahigh-voltage (UHV) SiC devices with hybrid unipolar/bipolar operation are introduced and demonstrated. As the first step of such a device, a merged p-i-n Schottky (MPS) diode with an epitaxial p+-anode layer is proposed to reduce the conduction loss of a bipolar device in the low current region. A 'snapback' phenomenon is intensively investigated by analytical modeling, device simulation, and experiment and a design guideline of snapback-free hybrid operating MPS diodes is presented. Using the design guideline, snapback-free MPS diodes are fabricated and forward characteristics are investigated. By using a proper edge termination structure, a UHV SiC MPS diode with breakdown voltage of 11.3 kV is demonstrated.

DOI： 10.1109/TED.2016.2636573

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations

Horita Masahiro, Takashima Shinya, Tanaka Ryo, Matsuyama Hideaki, Ueno Katsunori, Edo Masaharu, Takahashi Tokio, Shimizu Mitsuaki, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 56 ( 3 ) 2017.3

Analysis of High-Field Hole Transport in Germanium and Silicon Nanowires Based on Boltzmann's Transport Equation

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. 16 ( 1 ) page： 118 - 125 2017.1

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

In this paper, high-field hole transport in germanium nanowires was studied by using Boltzmann's transport equation in an atomistic framework. The scattering mechanisms taken into account are phonon and surface roughness. The hole drift velocities of [110], [111], and [112]-oriented germanium nanowires showed negative-differential characteristics, while that of the [001] nanowire did not. The behavior of hole drift velocity was analyzed based on the highly nonparabolic and orientation-dependent valence band structure. High-field hole transport properties in silicon nanowires were also calculated, and the differences between germanium and silicon nanowires were discussed, focusing mainly on momentum and energy relaxation times. The [110], [111], and [112] silicon nanowires showed faster hole drift velocity at high field than the germanium nanowires with the same orientation. This was attributed to faster energy relaxation in silicon nanowires, which mitigates the negative differential mobility in silicon nanowires compared to germanium nanowires.

DOI： 10.1109/TNANO.2016.2635110

Phonon frequencies of a highly strained AIN layer coherently grown on 6H-SiC (0001)

Kaneko M., Kimoto T., Suda J.

AIP ADVANCES Vol. 7 ( 1 ) 2017.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AIP Advances

Phonon frequencies of a high-quality AlN layer coherently grown on a 6H-SiC (0001) substrate are investigated by Raman scattering. Owing to the largest strain in our coherent AlN layer among heteroepitaxially grown AlN layers ever reported, phonon frequencies of the E2 (low), E2 (high), and A1 (LO) modes are considerably shifted to 244.5 (−3.3, compared with bulk AlN), 672.1 (+16.3), and 899 (+11)cm−1, respectively. Full widths at half maximum of the phonon modes in the coherent AlN are almost equal to those of high-quality bulk AlN, clearly indicating its high crystalline quality and uniform strain. We discuss accuracy of phonon deformation potentials reported by several other groups thorough comparing our experimental results.

DOI： 10.1063/1.4974500

Characterization of lightly-doped n- and p-type homoepitaxial GaN on free-standing substrates

Horita Masahiro, Suda Jun

2017 IEEE INTERNATIONAL MEETING FOR FUTURE OF ELECTRON DEVICES, KANSAI (IMFEDK) page： 86 - 87 2017

Analysis of quasi-ballistic hole transport capability of Ge and Si nanowire pMOSFETs by a quantum-corrected Boltzmann transport equation

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

2017 INTERNATIONAL CONFERENCE ON SIMULATION OF SEMICONDUCTOR PROCESSES AND DEVICES (SISPAD 2017) page： 277 - 280 2017

Correlation between shapes of Shockley stacking faults and structures of basal plane dislocations in 4H-SiC epilayers

Iijima Akifumi, Kamata Isaho, Tsuchida Hidekazu, Suda Jun, Kimoto Tsunenobu

PHILOSOPHICAL MAGAZINE Vol. 97 ( 30 ) page： 2736 - 2752 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Philosophical Magazine

Shockley-type stacking faults expanded in 4H–SiC epilayers induced by ultraviolet illumination were investigated using a photoluminescence imaging method, a photoluminescence mapping method and X-ray topography. After ultraviolet illumination, more than 30 patterns of Shockley-type stacking faults which expanded from perfect basal plane dislocations were observed by photoluminescence imaging. The initial basal plane dislocations were crystallographically classified, and individual shapes of expanded Shockley-type stacking faults were predicted. The correspondence between the predicted shapes and observed ones was discussed.

DOI： 10.1080/14786435.2017.1350788

Insight into phonon scattering in Si nanowires through high-field hole transport: Impacts of boundary condition and comparison with bulk phonon approximation

Tanaka H., Suda J., Kimoto T.

33RD INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS Vol. 864 ( 1 ) 2017

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

The impact of how to model phonon scattering on hole transport in Si nanowires was studied based on Boltzmann's transport equation. Boundary conditions for atomistic description of phonons in nanowires and approximation by bulk acoustic and optical phonons were analyzed in terms of their impacts on high-field hole transport. The boundary conditions for phonons influence the drift velocity and momentum relaxation time, especially at low electric field, but the energy relaxation time hardly depends on the boundary conditions. The impacts by the change of boundary conditions can be approximated by the change of the strength of acoustic phonon scattering in bulk phonon picture, though the behavior of energy relaxation and distribution function of holes can not be reproduced by bulk phonon approximation.

DOI： 10.1088/1742-6596/864/1/012046

Theoretical Analysis of Quasi-ballistic Hole Transport in Ge and Si Nanowires Focusing on Energy Relaxation Process

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

2017 SILICON NANOELECTRONICS WORKSHOP (SNW) page： 35 - 36 2017

Impact of annealing temperature on surface passivation of SiC epitaxial layers with deposited SiO<inf>2</inf> followed by POCl<inf>3</inf> annealing

Okuda T., Kobayashi T., Kimoto T., Suda J.

WiPDA 2016 - 4th IEEE Workshop on Wide Bandgap Power Devices and Applications page： 233 - 235 2016.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WiPDA 2016 - 4th IEEE Workshop on Wide Bandgap Power Devices and Applications

We investigate an impact of annealing temperature on surface passivation of SiC epitaxial layers with deposited SiO2 followed by POCl3 annealing. The POCl3 annealing process consists of two steps: (i) thermal annealing in POCl3 and (ii) subsequent thermal annealing in pure N2. We find that the annealing temperature of the subsequent N2 annealing is important to reduce surface recombination on SiC. For surface passivation, N2 annealing at high temperature at 1000° C is necessary.

DOI： 10.1109/WiPDA.2016.7799944

Control of carbon vacancy in SiC toward ultrahigh-voltage power devices

Kimoto T., Kawahara K., Zippelius B., Saito E., Suda J.

SUPERLATTICES AND MICROSTRUCTURES Vol. 99 page： 151 - 157 2016.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Superlattices and Microstructures

A carbon vacancy defect is one of the most abundant point defects in SiC (as-grown, irradiated, annealed) and of technological importance because the acceptor-like level of a carbon monovacancy (Z1/2 center: EC – 0.63 eV) works as the primary carrier-lifetime killer in 4H–SiC. The carbon vacancy defects can be preferentially generated by either low-energy electron irradiation or high-temperature treatment in an inert gas ambient. On the other hand, the carbon vacancy defects can be almost eliminated by either a carbon-ion implantation process or thermal oxidation. By combination of these techniques, the density of carbon vacancy defects can be controlled in the wide range from 1011 cm−3 to 1015 cm−3 or even higher.

DOI： 10.1016/j.spmi.2016.03.029

Promise and Challenges of High-Voltage SiC Bipolar Power Devices

Kimoto Tsunenobu, Yamada Kyosuke, Niwa Hiroki, Suda Jun

ENERGIES Vol. 9 ( 11 ) 2016.11

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

Although various silicon carbide (SiC) power devices with very high blocking voltages over 10 kV have been demonstrated, basic issues associated with the device operation are still not well understood. In this paper, the promise and limitations of high-voltage SiC bipolar devices are presented, taking account of the injection-level dependence of carrier lifetimes. It is shown that the major limitation of SiC bipolar devices originates from band-to-band recombination, which becomes significant at a high-injection level. A trial of unipolar/bipolar hybrid operation to reduce power loss is introduced, and an 11 kV SiC hybrid (merged pin-Schottky) diodes is experimentally demonstrated. The fabricated diodes with an epitaxial anode exhibit much better forward characteristics than diodes with an implanted anode. The temperature dependence of forward characteristics is discussed.

DOI： 10.3390/en9110908

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations (Retraction of vol 55, 05FH03, 2016)

Horita Masahiro, Takashima Shinya, Tanaka Ryo, Matsuyama Hideaki, Ueno Katsunori, Edo Masaharu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 55 ( 11 ) 2016.11

Franz-Keldysh effect in n-type GaN Schottky barrier diode under high reverse bias voltage (vol 9, 091002, 2016)

Maeda Takuya, Okada Masaya, Ueno Masaki, Yamamoto Yoshiyuki, Horita Masahiro, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 9 ( 10 ) 2016.10

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

The reduced effective masses (μhh-e and μlh-e) were incorrect in the original manuscript. Table I and Fig. 4 should be replaced with the table and the figure shown below. The description "using a reduced effective mass of 0.14m0, which is calculated from the masses reported for electrons and holes in GaN" in line 44, column 1, page 1 should be replaced with "using the effective masses reported for electrons and holes in GaN, which are listed in Table I", and "a reduced effective mass of GaN (μ∥ = 0.14m0) was used" in line 34, column 2, page 3 should be replaced with "calculation was done by the two-band-model using the effective masses listed in Table I". The calculations of the absorption coefficient and the photocurrent was done by the two-hole-band-model using me, mhh, and mlh. The correction does not affect the results and conclusions in this paper.

DOI： 10.7567/APEX.9.109201

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