Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Growth, Electrical Characterization, and Electroluminescence of GaN/SiC Heterojunction Diodes and Bipolar Transistors Fabricated on SiC Off-Axis Substrates

Miyake Hiroki, Amari Koichi, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 52 ( 12 ) 2013.12

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

The growth, electrical characterization, and electroluminescence (EL) of GaN/SiC heterojunction bipolar transistors (HBTs) are presented. GaN grown on off-axis SiC by molecular beam epitaxy showed step bunching owing to the large off-angle of SiC substrates, which contributed to the annihilation of edge dislocations. We investigated the impact of base doping concentration and SiC polytype (4H and 6H) on the characteristics of GaN/SiC heterojunction diodes. By utilizing a reduced doping concentration of 1 × 1018 cm -3 instead of 1 × 1019 cm-3, we suppressed the tunneling current via interface traps, resulting in an improved rectifying behavior in the diodes. Capacitance-voltage (C-V) and EL characteristics revealed that the band lineup of GaN/SiC is of type II, and 6H-SiC is better for electron injection. In accordance with diode characteristics, the fabricated GaN/SiC HBTs showed an improved common-base current gain of 0.03 by employing a reduced base doping concentration of 1 × 1018 cm-3 and 6H-SiC, whereas a current gain below 1 × 10-4 was obtained in the HBTs with a base doping concentration of 1 × 1019 cm-3. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.124102

Improvement of Carrier Lifetimes in Highly Al-Doped p-Type 4H-SiC Epitaxial Layers by Hydrogen Passivation

Okuda Takafumi, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 6 ( 12 ) 2013.12

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

Carrier lifetimes in a highly Al-doped p-type epilayer (NA = 1 × 1018 cm-3) are investigated by differential microwave photoconductance decay (μ-PCD) measurements. A carrier lifetime of 310 ns in the as-grown p-type epilayer decreases to 90 ns by thermal treatment in Ar, O2, or N2 atmospheres (>700 °C), and recovers to 300 ns by H2 annealing (>750 °C). Hydrogen is detected at a concentration of (2-3) × 1015 cm-3 in the H2-annealed epilayer. These results suggest that a lifetime killer exists in the p-type epilayer, limiting the carrier lifetime to 90 ns and is passivated by hydrogen annealing, resulting in the improved carrier lifetime of 300 ns. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.121301

Size and geometric effects on conduction band structure of GaAs nanowires

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

IMFEDK 2013 - 2013 International Meeting for Future of Electron Devices, Kansai page： 118 - 119 2013.10

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IMFEDK 2013 - 2013 International Meeting for Future of Electron Devices, Kansai

The conduction band structure of GaAs nanowires with various cross-sectional shapes and orientations was calculated by a tight-binding model and an effective mass equation taking the bulk full-band structure into account. The effective mass of nanowires increases as the cross-sectional size decreases. However, the amount of the increase in mass is strongly dependent on the wire orientations and substrate faces of nanowires, which originates from the anisotropy of Γ valley of bulk GaAs. © 2013 IEEE.

DOI： 10.1109/IMFEDK.2013.6602267

AlGaN/SiC Heterojunction Bipolar Transistors Featuring AlN/GaN Short-Period Superlattice Emitter

Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 60 ( 9 ) page： 2768 - 2775 2013.9

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

Growth and electrical characterization of aluminum gallium nitride (AlGaN)/SiC heterojunction bipolar transistors (HBTs) featuring AlN/GaN short-period superlattice as a quasi-AlGaN emitter are presented. The AlN/GaN superlattice emitter was grown by molecular beam epitaxy on off-axis SiC, which showed adequate structural and electronic properties as the emitter of the HBTs. We investigated the impact of Al composition in the emitter on the transport characteristics and current gain of the HBTs. Using Al composition of over 0.5, we achieved type-I band alignment in AlGaN/SiC, and suppressed the tunneling current via interface traps, resulting in an improved current gain of up to 2.7. Toward further improvement of current gain, we also investigated the effect of n-SiC spacer between n-AlGaN and p-SiC and p-SiC base width. Using 200-nm-thick n-SiC spacer and 250-nm-thick p-SiC base layer, we achieved an improved current gain of 13 owing to the reduced interface and bulk recombination. © 1963-2012 IEEE.

DOI： 10.1109/TED.2013.2273499

Single-crystalline 4H-SiC micro cantilevers with a high quality factor

Adachi Kohei, Watanabe Naoki, Okamoto Hajime, Yamaguchi Hiroshi, Kimoto Tsunenobu, Suda Jun

SENSORS AND ACTUATORS A-PHYSICAL Vol. 197 page： 122 - 125 2013.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Sensors and Actuators, A: Physical

Single-crystalline 4H-SiC micro cantilevers were fabricated by doping-type selective electrochemical etching of 4H-SiC. Using this method, n-type 4H-SiC cantilevers were fabricated on a p-type 4H-SiC substrate, and resonance characteristics of the fabricated 4H-SiC cantilevers were investigated under a vacuum condition. The resonant frequencies agreed very well with the results of numerical simulations. The maximum quality factor in first-mode resonance of the 4H-SiC cantilevers was 230,000. This is 10 times higher than the quality factor of conventional 3C-SiC cantilevers fabricated on an Si substrate. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sna.2013.04.014

Coherent Growth of AlN/GaN Short-Period Superlattice with Average GaN Mole Fraction of up to 20% on 6H-SiC(0001) Substrates by Plasma-Assisted Molecular-Beam Epitaxy

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 52 ( 8 ) 2013.8

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

To obtain a high-crystalline-quality AlN/GaN short-period superlattice with higher average GaN mole fraction, the effects of the thicknesses of AlN barrier and GaN well layers on the superlattice growth were investigated. Coherent growth with an average GaN mole fraction of 20% was realized by reducing the AlN barrier layer thickness to 8 bilayers (BL) while keeping the GaN well layer thickness at 2 BL. Further reduction in the AlN barrier layer thickness resulted in lattice relaxation and degradation of the crystalline quality. Grown layers with various well and barrier thicknesses were investigated by transmission electron microscopy, X-ray diffraction, and atomic force microscopy. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.08JE21

Ultrahigh-Voltage SiC PiN Diodes with an Improved Junction Termination Extension Structure and Enhanced Carrier Lifetime

Kaji Naoki, Niwa Hiroki, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 52 ( 7 ) 2013.7

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

Ultrahigh-voltage SiC PiN diodes with an improved junction termination extension (JTE) structure and improved forward characteristics are presented in this paper. An improved space-modulated JTE (SM-JTE) structure was designed by device simulation, and a breakdown voltage of over 17 kV was obtained in a wider range of JTE dose with the improved SM-JTE. In addition, a lifetime enhancement process (thermal oxidation) was performed to improve the forward characteristics. The on-resistance of the SiC PiN diodes with the lifetime enhancement process was reduced to 13m°Cm2 at 150°C compared with that of the SiC PiN diodes with the conventional process (32m°Cm2). © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.070204

Optical Properties of Highly Strained AlN Coherently Grown on 6H-SiC(0001)

Kaneko Mitsuaki, Okumura Hironori, Ishii Ryota, Funato Mitsuru, Kawakami Yoichi, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 6 ( 6 ) 2013.6

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

The optical properties of wurtzite AlN under large compressive strain are investigated by photoluminescence and optical reflectivity measurements with two different geometries. The AlN layer was coherently grown on 6H-SiC(0001), resulting in strains of ∈xx = ∈yy = -9.6 × 10-3 and ∈zz = 5.12 × 10-3, as confirmed by high-resolution X-ray diffraction. Free exciton transitions were clearly observed. The transition energy of A free exciton (with Γ1 symmetry) was estimated to be 6.246 eV at 10 K. The large energy shift of the free exciton transition with respect to the transition in unstrained AlN was well explained by the reported deformation potentials of AlN. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.062604

Deep Levels Generated by Thermal Oxidation in n-Type 4H-SiC

Kawahara Koutarou, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS EXPRESS Vol. 6 ( 5 ) 2013.5

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

The Z1/2 center (EC - 0:67 eV), which is a lifetime killer in n-type 4H-SiC epilayers, is reduced by thermal oxidation. The oxidation, however, simultaneously generates other deep levels: ON1 (E C - 0:84 eV) and ON2 (EC - 1:1 eV) centers. From the behaviors (generation condition, thermal stability, and change in the depth profiles) of the ON1 and ON2 centers in samples (i) oxidized in O2, (ii) implanted with C+ or Si+ atoms, and (iii) oxidized in N2O (or NO), we suggest that these defects may originate from the same defect in different charge states, related to both carbon interstitials and N atoms. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.051301

Investigation on origin of Z(1/2) center in SiC by deep level transient spectroscopy and electron paramagnetic resonance

Kawahara Koutarou, Xuan Thang Trinh, Nguyen Tien Son, Janzen Erik, Suda Jun, Kimoto Tsunenobu

APPLIED PHYSICS LETTERS Vol. 102 ( 11 ) 2013.3

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

The Z1/2 center in n-type 4H-SiC epilayers-a dominant deep level limiting the carrier lifetime-has been investigated. Using capacitance versus voltage (C-V) measurements and deep level transient spectroscopy (DLTS), we show that the Z1/2 center is responsible for the carrier compensation in n-type 4H-SiC epilayers irradiated by low-energy (250 keV) electrons. The concentration of the Z1/2 defect obtained by C-V and DLTS correlates well with that of the carbon vacancy (VC) determined by electron paramagnetic resonance, suggesting that the Z1/2 deep level originates from VC. © 2013 American Institute of Physics.

DOI： 10.1063/1.4796141

Effects of Nitridation on 4H-SiC MOSFETs Fabricated on Various Crystal Faces

Nanen Yuichiro, Kato Muneharu, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 60 ( 3 ) page： 1260 - 1262 2013.3

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

Effects of nitric oxide (NO) and nitrous oxide (N2O) annealing on 4H-SiCmetal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated on the (0001), (000-1), and (11-20) faces are investigated. MOSFETs on (11-20) exhibited high channel mobility (108 cm2/V s) compared to those on (0001) (29-37 cm2/V s) and (000-1) (39-46 cm2/V s). The MOSFET characteristics are discussed in terms of oxidation taking place during the nitridation annealing and crystal faces.

DOI： 10.1109/TED.2012.2236333

Orientation and Shape Effects on Ballistic Transport Properties in Gate-All-Around Rectangular Germanium Nanowire nFETs

Mori Seigo, Morioka Naoya, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 60 ( 3 ) page： 944 - 950 2013.3

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

The electron transport properties of square and rectangular cross-sectional germanium nanowire (GeNW) field-effect transistors (FETs) with [001], [110], [111], and [112] crystal orientations are investigated. The electronic states of GeNWs are calculated by using an sp^{3}d^{5}s\ast tight-binding model coupled to a Poisson equation self-consistently. A semiclassical ballistic FET model is used to evaluate the electron transport characteristics. For the square cross section, electron injection velocity dominates the drive current in GeNW FETs because the inversion electron density in the GeNW channels is mainly determined by the capacitance of the gate insulator, and a [110] GeNW FET achieves the highest drive current of all the orientations. In the case of rectangular cross section, the electron density in GeNWs is dependent on their orientations and cross-sectional geometries due to the small quantum capacitance, and the difference of the density of states of GeNWs significantly affects the drive current. A [112] GeNW FET on a (\hbox{1}\bar{\hbox{1}}\hbox{0} ) face exhibits the highest injection velocity of all the calculated FETs but low drive current because of its insufficient density of states. As a result, a [110] GeNW FET on a (001) face, which has both large density of states and high injection velocity, achieves the highest drive current. © 1963-2012 IEEE.

DOI： 10.1109/TED.2013.2237779

Deep levels generated by thermal oxidation in p-type 4H-SiC

Kawahara Koutarou, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 113 ( 3 ) 2013.1

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

Thermal oxidation is an effective method to reduce deep levels, especially the Z1/2-center (EC - 0.67 eV), which strongly suppresses carrier lifetimes in n-type 4H-SiC epilayers. The oxidation, however, simultaneously generates other deep levels, HK0 (EV + 0.79 eV) and HK2 (EV + 0.98 eV) centers, within the lower half of the bandgap of SiC, where the HK0 center is a dominant deep level with a concentration of about 1 × 1013 cm-3 after oxidation. By comparing deep levels observed in three sets of p-type 4H-SiC: oxidized, electron-irradiated, and C+- or Si+-implanted samples, we find that the HK0 and HK2 centers are complexes including carbon interstitials such as the di-carbon interstitial or di-carbon antisite. Other defects observed in p-type 4H-SiC after electron irradiation or after C+/Si+ implantation are also studied. © 2013 American Institute of Physics.

DOI： 10.1063/1.4776240

Long Photoconductivity Decay Characteristics in p-Type 4H-SiC Bulk Crystals

Okuda Takafumi, Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 52 ( 1 ) 2013.1

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

We investigated the photoconductivity decay characteristics of p-type 4H-SiC bulk crystals by differential microwave photoconductance decay (μ-PCD) measurements using a 349-nm laser as an excitation source. The decay time at room temperature was 2600 μs, which is much longer than that of n-type 4H-SiC bulk crystals (40 ns). Decay time decreased with increasing temperature, resulting in 120 μs at 250 °C, and the activation energy of decay time was determined to be 140 ± 10 meV. Long decay characteristics were also observed by below-band-gap excitation at 523 nm. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.010202

Junction technology in SiC for high-voltage power devices

Kimoto T., Kawahara K., Niwa H., Okuda T., Suda J.

Extended Abstracts of the 13th International Workshop on Junction Technology 2013, IWJT 2013 page： 54 - 57 2013

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Extended Abstracts of the 13th International Workshop on Junction Technology 2013, IWJT 2013

In electric power conversion systems of power infrastructures, electric vehicles, and power supplies, Si-based power semiconductor devices are employed as a key hardware. Reduction of power dissipation in the conversion systems is strongly required for energy saving. In particular, ultrahigh-voltage power converters with high efficiency are essential to realize a stable and highly efficient electric power network by optimizing the use of solar power and wind-generated power in the future. The efficiency of power converters/inverters strongly relies on the performance of power semiconductor devices employed in the power electronic systems. Silicon carbide (SiC) is a newly-emerging wide bandgap semiconductor, by which high-voltage, low-loss power devices can be realized owing to its superior properties [1-3]. The major features of SiC power devices include high-voltage blocking capability, low on-state resistance, fast switching speed, and high-temperature operation. © 2013 IEEE.

DOI： 10.1109/IWJT.2013.6644492

Size and Geometric Effects on Conduction Band Structure of GaAs Nanowires

Tanaka Hajime, Morioka Naoya, Mori Seigo, Suda Jun, Kimoto Tsunenobu

2013 IEEE INTERNATIONAL MEETING FOR FUTURE OF ELECTRON DEVICES, KANSAI (IMFEDK2013) 2013

21-kV SiC BJTs With Space-Modulated Junction Termination Extension

Miyake Hiroki, Okuda Takafumi, Niwa Hiroki, Kimoto Tsunenobu, Suda Jun

IEEE ELECTRON DEVICE LETTERS Vol. 33 ( 11 ) page： 1598 - 1600 2012.11

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

We report here 20-kV-class small-area (0.035 mm 2 ) 4H-SiC bipolar junction transistors. We implemented edge termination techniques featuring two-zone junction termination extension and space-modulated rings. on-state characteristics showed a current gain of 63 and a specific on-resistance of 321 mΩ cm 2, which is slightly below the SiC unipolar limit. We achieved the open-base blocking voltage of 21 kV at a leakage current of 0.1 mA/cm 2 , which is the highest blocking voltage among any semiconductor switching devices. © 2012 IEEE.

DOI： 10.1109/LED.2012.2215004

Thermo-Optic Coefficients of 4H-SiC, GaN, and AIN for Ultraviolet to Infrared Regions up to 500 degrees C

Watanabe Naoki, Kimoto Tsunenobu, Suda Jun

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 51 ( 11 ) 2012.11

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

The temperature dependence of the refractive indices of 4H-SiC, GaN, and AlN were determined in a wavelength range from the near band edge (392 nm for 4H-SiC, 367nm for GaN, and 217nm for AlN) to infrared (1700 nm) and a temperature range from room temperature to 500 °C. Optical interference measurements with vertical incidence along a c-axis configuration were employed to precisely evaluate ordinary refractive indices. Near the band-edge region, the temperature dependence of the refractive index mainly originates from the temperature change of the bandgap. At 450 nm, the thermo-optic coefficients of 4H-SiC, GaN, and AlN were measured to be 7:8 × 10 -5, 1:6 × 10 -4, and 3:6 × 10 -5 K -1, respectively. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.112101

Negative-U System of Carbon Vacancy in 4H-SiC

Son N. T., Trinh X. T., Lovlie L. S., Svensson B. G., Kawahara K., Suda J., Kimoto T., Umeda T., Isoya J., Makino T., Ohshima T., Janzen E.

PHYSICAL REVIEW LETTERS Vol. 109 ( 18 ) 2012.10

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

Using electron paramagnetic resonance (EPR), energy levels of the carbon vacancy (V C) in 4H-SiC and its negative-U properties have been determined. Combining EPR and deep-level transient spectroscopy we show that the two most common defects in as-grown 4H-SiC-the Z 1/2 lifetime-limiting defect and the EH 7 deep defect-are related to the double acceptor (2-|0) and single donor (0|+) levels of V C, respectively. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.109.187603

Orientation and size effects on ballistic electron transport properties in gate-all-around rectangular germanium nanowire FETs

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

2012 IEEE Silicon Nanoelectronics Workshop, SNW 2012 2012.10

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：2012 IEEE Silicon Nanoelectronics Workshop, SNW 2012

We calculated the conduction band structure of GeNWs by a tight-binding model and obtained the fundamental understanding of electron transport characteristics in [001], [110], [111], and [112] GeNW FETs. The simulation of ballistic electron transport revealed that [110] GeNW FETs on the (001) face achieve high drive current as well as high injection velocity, being the best choice for n-channel FETs. © 2012 IEEE.

DOI： 10.1109/SNW.2012.6243360

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