Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Theoretical analysis of high-field hole transport in germanium and silicon nanowires

Tanaka H., Suda J., Kimoto T.

2016 IEEE Silicon Nanoelectronics Workshop, SNW 2016 page： 192 - 193 2016.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2016 IEEE Silicon Nanoelectronics Workshop, SNW 2016

High-field hole transport in Ge nanowires was studied using Boltzmann's transport equation. The behavior of drift velocity was analyzed based on the highly non-parabolic valence band structure. High-field hole transport properties in Si nanowires were also calculated, and the differences between Ge and Si nanowires were discussed.

DOI： 10.1109/SNW.2016.7578046

Analysis of ballistic and quasi-ballistic hole transport properties in germanium nanowires based on an extended "Top of the Barrier" model

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

SOLID-STATE ELECTRONICS Vol. 123 page： 143 - 149 2016.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Solid-State Electronics

The ballistic hole transport properties in rectangular cross-sectional germanium nanowire transistors with various geometries were studied based on the “Top of the Barrier” model. Then, by an extension of this model, the quasi-ballistic hole transport was discussed taking into account phonon and surface roughness scattering in the channel and source-to-drain direct tunneling. Among several nanowire geometries targeted in this study, the [1 1 0]-oriented nanowire with large height along [11¯0] ([1 1 0]/(1 1¯ 0) NW) exhibited the largest ballistic current. This was understood from its large density of states and resulting high hole density. Large density of states, however, enhances backscattering in the channel. An approximation analysis of quasi-ballistic transport suggested that the [1 1 0]/(0 0 1) NW with higher mobility can outperform [1 1 0]/(1 1¯ 0) NW when scattering and tunneling are considered.

DOI： 10.1016/j.sse.2016.04.015

Franz-Keldysh effect in n-type GaN Schottky barrier diode under high reverse bias voltage

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

APPLIED PHYSICS EXPRESS Vol. 9 ( 9 ) 2016.9

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

The photocurrent of GaN vertical Schottky barrier diodes was investigated under sub-bandgap wavelength light irradiation. Under a low reverse bias voltage, the photocurrent is induced by internal photoemission, while under a high reverse bias voltage, the photocurrent increases significantly with the bias voltage. This is due to sub-bandgap optical absorption in a depletion region due to the Franz-Keldysh effect. The voltage and wavelength dependences of the photocurrent are successfully explained quantitatively.

DOI： 10.7567/APEX.9.091002

SiC and GaN from the viewpoint of vertical power devices

Suda J.

Device Research Conference - Conference Digest, DRC Vol. 2016-August 2016.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Device Research Conference - Conference Digest, DRC

Wide-bandgap (WBG) semiconductors have attracted great attention as materials for the next-generation power devices since they have superior material properties compared to silicon (Si). The most advanced WBG semiconductor for power devices is silicon carbide (SiC). In 1987, the growth technology called 'step-controlled epitaxy', which enables single-phase (polytype) growth, was developed. In 1993-1994, SiC Schottky-barrier diodes (SBDs) which exceeds the Si material limit was demonstrated. In 2001, SiC SBDs were commercialized. Key technologies for SiC SBDs were edge termination to obtain an ideal breakdown voltage and a junction barrier Schottky (JBS) structure to suppress reverse leakage current. For power MOSFETs, it took longer time due to low channel mobility at SiO2/SiC and oxide reliability issues. Channel mobility was much improved by post-oxidation nitridation in NO or N2O ambient. Now, channel mobility and reliability are well controlled (balanced). SiC power MOSFETs as well as power modules with SiC MOSFETs and SiC SBDs, are commercially available. Last 5 years, the implementation of SiC devices into electronic vehicles and railway trains were extensively investigated, demonstrating a significant improvement of power efficiency.

DOI： 10.1109/DRC.2016.7548292

Characterization of n-type and p-type GaN layers grown on free-standing GaN substrates

Suda J., Horita M.

2016 Compound Semiconductor Week, CSW 2016 - Includes 28th International Conference on Indium Phosphide and Related Materials, IPRM and 43rd International Symposium on Compound Semiconductors, ISCS 2016 2016.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2016 Compound Semiconductor Week, CSW 2016 - Includes 28th International Conference on Indium Phosphide and Related Materials, IPRM and 43rd International Symposium on Compound Semiconductors, ISCS 2016

Electrical characterization of low-doped n-type and p-type GaN layers grown by metal-organic vapor phase epitaxy are presented. The GaN layers were grown on hydride-vapor-phase-epitaxy-grown free-standing GaN substrates. For n-type GaN, the impact of electron trap on electrical characterization is discussed. Charging of trap in a depletion layer affects C-V characteristics. Correction is needed for depth profiling of net donor concentration. For p-type GaN, hole mobility for various Mg doping concentrations at various temperatures are presented. At 300 K, 33 cm2/Vs is obtained for p-type GaN with Mg doping concentration of mid 1016 cm-3.

DOI： 10.1109/ICIPRM.2016.7528835

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 2016 page： 54 - 58 2016.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2016 16th International Workshop on Junction Technology, IWJT 2016

Electrical activation of implanted dopants and defect generation in SiC have been investigated. A nearly perfect (> 95%) electrical activation can be obtained including the implant tail region after annealing at 1650-1700 °C. The majority of point defects generated in implanted SiC can remarkably be reduced by thermal oxidation. The high activation ratio of implanted Al acceptors is a key factor for fabricating effective junction termination structures in high-voltage SiC devices. Recent high-quality semi-insulating SiC wafers offer the opportunity of high-temperature SiC integrated devices, which can be fabricated by only ion implantation without an epitaxial growth process.

DOI： 10.1109/IWJT.2016.7486673

Control of carrier lifetime of thick n-type 4H-SiC epilayers by high-temperature Ar annealing

Saito Eiji, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS EXPRESS Vol. 9 ( 6 ) 2016.6

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

We investigated the carrier lifetime and Z1/2 center density of thick n-type 4H-SiC epilayers, which were oxidized and subsequently annealed in Ar at high temperatures. The Z1/2 center density decreased below the detection limit in the region to, at least, a 130μm depth by thermal oxidation. After subsequent high-temperature annealing, the Z1/2 center density increased with increasing annealing temperature, while the distribution of the Z1/2 center density was nearly uniform to a 130μm depth. The carrier lifetime could be controlled from 26 to 2.4 μs by changing the annealing temperature from 1600 to 1800 °C.

DOI： 10.7567/APEX.9.061303

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, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 55 ( 5 ) 2016.5

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

Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016cm-3 (lightly doped) to 3.8 × 1019cm-3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of the p-GaN was 4 × 106cm-2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 160 to 450 K. A low compensation ratio of less than 1-was revealed. We also obtained the depth of the Mg acceptor level of 235 meV considering the lowering effect by the Coulomb potential of ionized acceptors. The hole mobilities of 33 cm2V-1 s-1 at 300K and 72cm2V-1 s-1 at 200K were observed in lightly doped p-GaN.

DOI： 10.7567/JJAP.55.05FH03

Strain control in AlN top layer by inserting an ultrathin GaN interlayer on an AlN template coherently grown on SiC(0001) by PAMBE

Kaneko Mitsuaki, Kimoto Tsunenobu, Suda Jun

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 253 ( 5 ) page： 814 - 818 2016.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (B) Basic Research

Abstractauthoren We propose partially relaxed ultrathin GaN interlayer for strain control of AlN on SiC substrates. According to the degree of relaxation of the GaN interlayer, the lattice constant of the interlayer changes from that of SiC to that of bulk GaN, which leads to strain control of an AlN top layer grown on the interlayer. Growth of these layers is conducted by plasma-assisted molecular beam epitaxy. Before growing the interlayer, an AlN layer coherently grown on SiC is used as a template layer. The interlayers that have different degrees of relaxation are successfully obtained by changing the interlayer thickness. As a result, strain values of the AlN top layer grown on the interlayers are widely controlled from compressive (-0.53%) to tensile (+ 0.07%). TEM observation revealed the relaxation is induced by U-shaped half-loop dislocations originating from the GaN interlayer.

DOI： 10.1002/pssb.201552649

Surface passivation on 4H-SiC epitaxial layers by SiO2 with POCl3 annealing

Okuda Takafumi, Kobayashi Takuma, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 9 ( 5 ) 2016.5

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

We investigated surface passivation on 4H-SiC epitaxial layers with deposited or thermally grown SiO2 followed by POCl3 annealing. The measured carrier lifetime in a p-type epilayer with deposited SiO2 was limited to 0.5 μs and it was improved to 3.0 μs after POCl3 annealing. In an n-type epilayer, a measured carrier lifetime of 5.8 μs was improved to 12 μs after POCl3 annealing. We found a clear relationship between the measured carrier lifetime and the interface state density at SiO2/n-SiC after POCl3 annealing, suggesting that the reduction in interface state density lowered the surface recombination velocity on the 4H-SiC.

DOI： 10.7567/APEX.9.051301

Interface state density of SiO2/p-type 4H-SiC (0001), (11(2)over-bar0), (1(1)over-bar00) metal-oxide-semiconductor structures characterized by low-temperature subthreshold slopes

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

APPLIED PHYSICS LETTERS Vol. 108 ( 15 ) 2016.4

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

Interface properties of heavily Al-doped 4H-SiC (0001) (Si-face), (1120) (a-face), and (1100) (m-face) metal-oxide-semiconductor (MOS) structures were characterized from the low-temperature gate characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs). From low-temperature subthreshold slopes, interface state density (Dit) at very shallow energy levels (ET) near the conduction band edge (Ec) was evaluated. We discovered that the Dit near Ec (Ec - 0.01 eV < ET < Ec) increases in MOS structures with higher Al doping density for every crystal face (Si-, a-, and m-face). Linear correlation is observed between the channel mobility and Dit near Ec, and we concluded that the mobility drop observed in heavily doped MOSFETs is mainly caused by the increase of Dit near Ec.

DOI： 10.1063/1.4946863

Modeling of surface roughness scattering in nanowires based on atomistic wave function: Application to hole mobility in rectangular germanium nanowires

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

PHYSICAL REVIEW B Vol. 93 ( 15 ) 2016.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physical Review B

The authors present a calculation model of surface roughness scattering (SRS) in nanowires (NWs) based on atomistic description of electronic states by an sp3d5s∗ tight-binding scheme, and then this model is applied to hole transport in rectangular cross-sectional germanium (Ge) NWs. In this SRS model, the change of electronic band structures due to width or height reduction is first computed, and then it is expressed using an equivalent potential near the surface. The perturbation corresponding to a surface roughness is calculated from this equivalent potential. Using the aforementioned SRS model, hole mobility in Ge NWs was computed taking into account phonon scattering and SRS. The impacts of SRS on hole mobility in Ge NWs were analyzed, focusing on the valence band structure and hole states of NWs. The main results are as follows. At low hole density, the impacts of SRS are strongly dependent on NW geometry, and Ge NWs with high phonon-limited hole mobility, such as rectangular cross-sectional [110]-oriented NWs with large height along the [001] direction and square cross-sectional [111]-oriented NWs, tend to be less affected by SRS. At high hole density, however, the geometry dependence of hole mobility becomes weaker. These are understood from the nature of hole states and the valence band structure.

DOI： 10.1103/PhysRevB.93.155303

Hall scattering factors in p-type 4H-SiC with various doping concentrations

Asada Satoshi, Okuda Takafumi, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 9 ( 4 ) 2016.4

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

The Hall scattering factor (γH) in p-type 4H-SiC with various aluminum doping concentrations of 5.8 ' 1014-7.1 ' 1018cm%3 was investigated from 300 to 900 K. γH was determined by comparing the Hall coefficient with the theoretical carrier concentration derived from acceptor and donor concentrations obtained from secondary ion mab spectrometry and capacitance-voltage measurements. γH decreased with increasing temperature or doping concentration; γH = 1-0.4 for the doping concentration of 5.8 ' 1014cm%3 and γH = 0.5-0.2 for the doping concentration of 7.1 ' 1018cm%3. The dependence might be caused by the anisotropic and nonparabolic valence band structure of 4H-SiC.

DOI： 10.7567/APEX.9.041301

Special issue on wide-bandgap semiconductor power electronics Preface

Suda Jun

SEMICONDUCTOR SCIENCE AND TECHNOLOGY Vol. 31 ( 3 ) 2016.3

Strong impact of the initial III/V ratio on the crystalline quality of an AlN layer grown by rf-plasma-assisted molecular-beam epitaxy

Kaneko Mitsuaki, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 9 ( 2 ) 2016.2

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

The initial Al/N ratio for AlN growth of plasma-assisted molecular-beam epitaxy without plasma stabilization is investigated. The in situ growth rate of AlN gradually increased and its temporal variation corresponded to that of nitrogen atoms, which indicated that the initial Al/N ratio was excessively Al-rich. For AlN growth, such a high-Al/N-ratio condition resulted in a three-dimensional growth mode in the initial stage of the growth, and AlN with high threading dislocation density was obtained. By controlling the initial Al/N ratio by introducing a short standby time, the resulting two-dimensional initial growth mode leads to high-quality growth of AlN.

DOI： 10.7567/APEX.9.025502

Characterization of N-Type and P-Type GaN Layers Grown on Free-Standing GaN Substrates

Suda Jun, Horita Masahiro

2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016

ESR study on hydrogen passivation of intrinsic defects in p-type and semi-insulating 4H-SiC

Murakami K., Tanai S., Okuda T., Suda J., Kimoto T., Umeda T.

Materials Science Forum Vol. 858 page： 318 - 321 2016

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

We studied the hydrogen passivation/depassivation of four types of intrinsic defects (EI5/6, HEI7/8, HEI9/10, and P6/7) in p-type and semi-insulating 4H-SiC by means of electron spin resonance (ESR) for examining the origin of carrier-lifetime-killing defects. We suggest that the HEI7/8 and P6/7 centers are the strongest candidate for the origin of the lifetime-killing defects.

DOI： 10.4028/www.scientific.net/MSF.858.318

Impact of Annealing Temperature on Surface Passivation of SiC Epitaxial Layers with Deposited SiO2 Followed by POCl3 Annealing

Okuda Takafumi, Kobayashi Takuma, Kimoto Tsunenobu, Suda Jun

2016 IEEE 4TH WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS (WIPDA) page： 233 - 235 2016

SiC and GaN from the Viewpoint of Vertical Power Devices

Suda Jun

2016 74TH ANNUAL DEVICE RESEARCH CONFERENCE (DRC) 2016

Theoretical Analysis of High-field Hole Transport in Germanium and Silicon Nanowires

Tanaka Hajime, Suda Jun, Kimoto Tsunenobu

2016 IEEE SILICON NANOELECTRONICS WORKSHOP (SNW) page： 192 - 193 2016

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