Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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Experimental Study on Various Junction Termination Structures Applied to 15 kV 4H-SiC PiN Diodes

Niwa Hiroki, Feng Gan, Suda Jun, Kimoto Tsunenobu

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 Vol. 717-720 page： 973 - 976 2012

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

Breakdown characteristics of 4H-SiC PiN diodes with various JTE structures have been investigated. By combining two-zone JTE and Space-Modulated JTE (SM-JTE), a breakdown voltage over 15 kV, corresponding to about 93 % of the parallel-plane breakdown voltage, was realized. The window of optimum JTE dose to obtain high breakdown voltage was widened, which indicates the robustness to the deviation of JTE dose. By comparing the breakdown voltage obtained by simulation and experimental results, impacts of the charge near the SiO 2/SiC interface are discussed. © (2012) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.717-720.973

On the Formation of Intrinsic Defects in 4H-SiC by High Temperature Annealing Steps

Zippelius B., Suda J., Kimoto T.

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 Vol. 717-720 page： 247 - 250 2012

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

In this paper the impact of high temperature annealing on the formation of intrinsic defects in 4H-SiC such as Z1/2 and EH6/7 is examined. Three epitaxial layers with various initial concentrations of the Z1/2- and EH6/7-centers (1011 - 1013 cm-3) are investigated by means of deep level transient spectroscopy (DLTS). It turns out that depending on the initial defect concentration, the high temperature annealing leads to a monotonic increase of the Z1/2- and EH6/7-concentration in a temperature range from 1600 to 1750°C. For higher temperatures, the resulting defect concentration is independent of the sample's initial values. Therefore, beside the growth conditions such as C/Si ratio, the thermal post-growth processing has a severe impact on the carrier lifetime and must be taken into account during device fabrication. © (2012) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.717-720.247

4H-SiC bipolar junction transistors with record current gains of 257 on (0001) and 335 on (000-1)

Miyake H., Kimoto T., Suda J.

Proceedings of the International Symposium on Power Semiconductor Devices and ICs page： 292 - 295 2011.12

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

We demonstrate 4H-SiC bipolar junction transistors (BJTs) with record current gains. Improved current gain was achieved by utilizing optimized device geometry as well as optimized surface passivation and 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. Current gain (β) of 257 was achieved 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, for the first time, BJTs on the (000-1)C-face that showed the highest β of 335 among the SiC BJTs ever reported. © 2011 IEEE.

DOI： 10.1109/ISPSD.2011.5890848

Epitaxial growth and defect control of SiC for high-voltage power devices

Kimoto T., Suda J.

Journal of the Vacuum Society of Japan Vol. 54 ( 6 ) page： 362 - 368 2011.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Vacuum Society of Japan

Recent progress in fast epitaxial growth and defect control of silicon carbide (SiC) toward development of high-voltage power devices is reviewed. In chemical vapor deposition of 4H-SiC on off-axis (0001), a high growth rate of 85 μm/h and a low background doping of 1 × 10 13 cm -3 are achieved. Conversion of basal-plane dislocations to threading edge dislocations and generation of stacking faults during epitaxial growth are discussed. Deep levels in as-grown n-type and p-type 4H-SiC epitaxial layers have been investigated. A lifetime-killing defect, Z 1/2 center, can be almost eliminated by thermal oxidation, which leads to significant increase in carrier lifetimes. The obtained carrier lifetimes are long enough to fabricate 10 kV-class bipolar devices. Control of carrier lifetimes by lowenergy electron irradiation is demonstrated.

DOI： 10.3131/jvsj2.54.362

Reliability of Nitrided Gate Oxides for N- and P-Type 4H-SiC(0001) Metal-Oxide-Semiconductor Devices

Noborio Masato, Grieb Michael, Bauer Anton J., Peters Dethard, Friedrichs Peter, Suda Jun, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 50 ( 9 ) 2011.9

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

In this paper, we have investigated reliability of n- and p-type 4H-SiC(0001) metal-oxide-semiconductor (MOS) devices with N2O-grown oxides and deposited oxides annealed in N2O. From the results of time-dependent dielectric breakdown (TDDB) tests, it is revealed that the N 2O-grown oxides have relatively-high reliability (4-30Ccm -2 for n- and p-MOS structures). In addition, the deposited SiO 2 on n- and p-SiC exhibited a high charge-to-breakdown of 70.0 and 54.9Ccm-2, respectively. The n/p-MOS structures with the deposited SiO2 maintained a high charge-tobreakdown of 19.9/15.1Ccm -2 even at 200 °C. The deposited SiO2 annealed in N2O has promise as the gate insulator for n- and p-channel 4HSiC(0001) MOS devices because of its high charge-to-breakdown and good interface properties. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.090201

Nonradiative recombination at threading dislocations in 4H-SiC epilayers studied by micro-photoluminescence mapping

Feng Gan, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 110 ( 3 ) 2011.8

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

Threading dislocations (TDs) in 4H-SiC epilayers have been investigated by means of micro-photoluminescence (-PL) mapping at room temperature. Enhanced nonradiative recombination at TDs was confirmed experimentally, resulting in a reduced local PL emission intensity in the -PL intensity map performed at 390 nm (near band-edge emission). The behavior of nonradiative recombination at TDs depends on the dislocation type: the screw type of TDs shows stronger effect on the nonradiative recombination activity than the edge type, evidencing a larger local reduction of PL emission intensity. Furthermore, the contrast of TDs in the μ-PL intensity map greatly depends on the carrier lifetimes of the 4H-SiC epilayers. Lifetimes longer than 0.5 s are essential to obtain a discernible contrast for the individual TDs. © 2011 American Institute of Physics.

DOI： 10.1063/1.3622336

4H-SiC BJTs With Record Current Gains of 257 on (0001) and 335 on (0001)

Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

IEEE ELECTRON DEVICE LETTERS Vol. 32 ( 7 ) page： 841 - 843 2011.7

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

We demonstrate 4H-SiC bipolar junction transistors (BJTs) with record current gains. An improved current gain was achieved by utilizing optimized device geometry and continuous epitaxial growth of the emitterbase junction, combined with an intentional deep-level-reduction process based on thermal oxidation to improve the lifetime in p-SiC base. A current gain (β) of 257 was achieved for 4H-SiC BJTs fabricated on the (0001) Si face. A gain of 257 is twice as large as the previous record gain. We also demonstrate BJTs on the (0001) C face that showed the highest β of 335 among the SiC BJTs ever reported. © 2011 IEEE.

DOI： 10.1109/LED.2011.2142291

Anomalously low Ga incorporation in high Al-content AlGaN grown on (11(2)over-bar0) non-polar plane by molecular beam epitaxy

Ueta Shunsaku, Horita Masahiro, Kimoto Tsunenobu, Suda Jun

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 208 ( 7 ) page： 1498 - 1500 2011.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (A) Applications and Materials Science

Crystalline orientation dependence of Ga incorporation in growth of high Al-content AlGaN was investigated. Growth was carried out by molecular-beam epitaxy (MBE) using elemental Al, Ga, and rf-plasma-excited nitrogen under various V/III ratios. 6H-SiC (0001), 4H-SiC (1√100) and 4H-SiC (11√20) were used as substrates. Ga incorporation increased with increase of V/III ratio in the layers grown on (0001) and (1√100) planes. On the other hand, Ga was not incorporated in the layer grown on (11√20) plane even when the layer was grown under a nitrogen rich condition, indicating much lower Ga incorporation on (11√20) plane than those of other planes. AlGaN with good quality was successfully grown on (1√100) plane. Utilization of (1√100) plane is suitable in MBE growth of AlGaN-based deep-ultraviolet light emitting devices. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.201001033

Impacts of reduction of deep levels and surface passivation on carrier lifetimes in p-type 4H-SiC epilayers

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

JOURNAL OF APPLIED PHYSICS Vol. 109 ( 11 ) 2011.6

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

Impacts of reduction of deep levels and surface passivation on carrier lifetimes in p-type 4H-SiC epilayers are investigated. The authors reported that the carrier lifetime in n-type epilayers increased by reduction of deep levels through thermal oxidation and thermal annealing. However, the carrier lifetimes in p-type epilayers were not significantly enhanced. In this study, in order to investigate the influence of surface passivation on the carrier lifetimes, the epilayer surface was passivated by different oxidation techniques. While the improvement of the carrier lifetime in n-type epilayers was small, the carrier lifetime in p-type epilayers were remarkably improved by appropriate surface passivation. For instance, the carrier lifetime was improved from 1.4 s to 2.6 s by passivation with deposited SiO2 annealed in NO. From these results, it was revealed that surface recombination is a limiting factor of carrier lifetimes in p-type 4H-SiC epilayers. © 2011 American Institute of Physics.

DOI： 10.1063/1.3583657

Lifetime-Killing Defects in 4H-SiC Epilayers and Lifetime Control by Low-Energy Electron Irradiation

Kimoto T.

Silicon Carbide Vol. 1 page： 267 - 286 2011.4

4H-SiC MISFETs with Nitrogen-Containing Insulators

Noborio M.

Silicon Carbide Vol. 2 page： 235 - 265 2011.3

Bandgap shift by quantum confinement effect in < 100 > Si-nanowires derived from threshold-voltage shift of fabricated metal-oxide-semiconductor field effect transistors and theoretical calculations

Yoshioka Hironori, Morioka Naoya, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 109 ( 6 ) 2011.3

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

Si-nanowire (Si-NW) MOSFETs, the cross-sectional size (square root of the cross-sectional area of NWs) of which was changed from 18 to 4 nm, were fabricated and characterized. Both n- and p-channel MOSFETs have shown a nearly ideal subthreshold swing of 63 mV/decade. The threshold voltage of n-/p-channel MOSFETs has gradually increased/decreased with decreasing the cross-sectional size. The bandgap shift from bulk Si has been derived from the threshold-voltage shift. The bandgap of Si-NWs was calculated by a density functional theory, tight binding method, and effective mass approximation. The calculated bandgap shows good agreement with that derived from threshold voltage. The theoretical calculation indicates that the bandgap is dominated by the cross-sectional size (area) and is not very sensitive to the shape within the aspect-ratio range of 1.0-2.5. © 2011 American Institute of Physics.

DOI： 10.1063/1.3559265

Quantum-confinement effect on holes in silicon nanowires: Relationship between wave function and band structure

Morioka Naoya, Yoshioka Hironori, Suda Jun, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS Vol. 109 ( 6 ) 2011.3

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

The authors theoretically studied the valence band structure and hole effective mass of rectangular cross-sectional Si nanowires (NWs) with the crystal orientation of [110], [111], and [001]. The E-k dispersion and the wave function were calculated using an sp3d5s tight-binding method and analyzed with the focus on the nature of p orbitals constituting the subbands. In [110] and [111] nanowires, longitudinal/transverse p orbitals are well separated and longitudinal component makes light (top) subbands and transverse component makes heavy subbands. The heavy subbands are located far below the top light band when NW has square cross-section, but they gain their energy with the increase in the NW width and come near the band edge. This energy shift of heavy bands in [110] NWs shows strong anisotropy to the direction of quantum confinement whereas that in [111] NWs does not have such anisotropy. This anisotropic behavior and the difference among orientations are understandable by the character of the wave function of heavy subbands. Regarding the [001] nanowires, the top valence state is formed by the mixture of longitudinal/transverse p orbitals, which results in heavy effective mass and large susceptibility to lateral-size variation. The correlation of the wave function of hole states between nanowires and bulk is also discussed briefly. © 2011 American Institute of Physics.

DOI： 10.1063/1.3552593

Improvement of Current Gain in 4H-SiC BJTs by Surface Passivation With Deposited Oxides Nitrided in N2O or NO

Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

IEEE ELECTRON DEVICE LETTERS Vol. 32 ( 3 ) page： 285 - 287 2011.3

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

We report the improvement of current gain in 4H-SiC bipolar junction transistors (BJTs) by utilizing deposited oxides as a surface passivation layer. Various postdeposition annealing processes, including annealing ambient (N 2, N2O, and NO) and annealing time, were investigated. We successfully demonstrate SiC BJTs with high current gains β of 73 and 102 using deposited oxides annealed in N2O and NO, respectively, whereas BJTs having conventional thermally grown oxides showed a current gain of 50. © 2006 IEEE.

DOI： 10.1109/LED.2010.2101575

Origin of Etch Hillocks Formed on On-Axis SiC(000(1)over-bar) Surfaces by Molten KOH Etching

Suda Jun, Shoji Haruki, Kimoto Tsunenobu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 50 ( 3 ) 2011.3

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

Molten KOH etching of 6H- and 4H-SiC{0001} on-axis substrates was investigated. After molten KOH etching, etch pits originating from threading dislocations (TDs) and basal-plane dislocations (BPDs) were observed on (0001) surfaces. On the other hand, large and small hillocks were observed on (0001̄) surfaces. The etch hillocks consist of SiC, indicating slower etching at TDs. By comparing the (0001) side and (0001̄) side of the same substrate, it was found that large hillocks correspond to edge-type TDs, while small hillocks correspond to screw-type TDs. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.038002

Reduction of Threading Dislocation Density in 2H-AlN Grown on 6H-SiC(0001) by Minimizing Unintentional Active-Nitrogen Exposure before Growth

Okumura Hironori, Kimoto Tsunenobu, Suda Jun

APPLIED PHYSICS EXPRESS Vol. 4 ( 2 ) 2011.2

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

300-nm-thick AlN layers were grown directly on 6H-SiC(0001) with six Si-C bilayer-height (1.5 nm) steps by rf-plasma-assisted molecular-beam epitaxy (MBE). To avoid unintentional active-nitrogen exposure, AlN was grown just after the nitrogen plasma ignition. By combining optimized Ga pre-deposition and no active-nitrogen exposure, layer-by-layer growth was realized from the first layer of AlN. Screw-type and edge-type threading dislocation densities in the AlN layer were reduced to 6 × 104 and 4 × 108 cm-2, respectively. Most of the edge-type dislocations were located at the step edge of the SiC substrate. The dislocation density of the AlN grown on the terrace of the SiC substrate was as low as 8 × 107 cm-2. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.4.025502

Temperature and injection level dependencies and impact of thermal oxidation on carrier lifetimes in p-type and n-type 4H-SiC epilayers

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

JOURNAL OF APPLIED PHYSICS Vol. 109 ( 1 ) 2011.1

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

Dependencies of temperature and injection level on carrier lifetimes in 50 μm thick p-type and n-type 4H-SiC epilayers have been investigated. The carrier lifetimes have been measured by differential microwave photoconductance decay measurements at various injection levels and temperatures. In both p-type and n-type epilayers, the carrier lifetimes gradually increased with increasing the injection level, which were naturally expected from the Shockley-Read-Hall (SRH) model, and after taking a maximum, the lifetimes dropped at the very high-injection level. In contrast, the carrier lifetimes exhibited continuous increase with elevating the temperature for both epilayers. In addition, the impact of thermal oxidation process on the carrier lifetimes has been also investigated. The thermal oxidation process, by which the Z1/2 and EH6/7 centers were remarkably reduced that had been observed in n-type 4H-SiC in our previous work, led to the improvement of the carrier lifetimes especially for n-type epilayers. The carrier lifetime reached 4.1 μs in p-type and 6.1 μs in n-type epilayers at 250 °C with an injection level of 1.8×1016 cm-3 through the thermal oxidation processing. © 2011 American Institute of Physics.

DOI： 10.1063/1.3524266

4H-SiC Bipolar Junction Transistors with Record Current Gains of 257 on (0001) and 335 on (000-1)

Miyake Hiroki, Kimoto Tsunenobu, Suda Jun

2011 IEEE 23RD INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND ICS (ISPSD) page： 292 - 295 2011

Fabrication of Electrostatic-actuated Single-crystalline 4H-SiC Bridge Structures by Photoelectrochemical Etching

Watanabe Naoki, Kimoto Tsunenobu, Suda Jun

MICROMACHINING AND MICROFABRICATION PROCESS TECHNOLOGY XVI Vol. 7926 2011

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

An electrostatic-actuated suspended bridge structure composed by single-crystalline silicon carbide (SiC) is fabricated. The structure is entirely made of homoepitaxially grown single-crystalline 4H-SiC. Electrical isolation between the suspended bridge and the base plate is established with a pnp junction formed by multiple ion implantation. The structure is fabricated by a combination of reactive ion etching (RIE) and doping-selective photoelectrochemical (PEC) etching. The suspended bridge is actuated by applying a voltage between the bridge and the base plate.

DOI： 10.1117/12.874543

Thermo-optic Coefficients of SiC, GaN, and AlN up to 512 degrees C from Infrared to Ultraviolet Region for Tunable Filter Applications

Watanabe Naoki, Kimoto Tsunenobu, Suda Jun

MICROMACHINING AND MICROFABRICATION PROCESS TECHNOLOGY XVI Vol. 7926 2011

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering

The temperature dependence of the refractive indices of 4H-SiC, GaN, and AlN were investigated in a wavelength range from the near band edge (392 nm for SiC, 367 nm for GaN, and 217 nm for AlN) to infrared (1700 nm) and a temperature range from room temperature to 512°C. Optical interference measurements with vertical incident configuration were employed to precisely evaluate ordinary refractive indices. In visible region, the thermo-optic coefficient of GaN has the largest value in these materials. Optical simulation of GaN-based tunable band-pass filter with AlGaN/GaN distributed Bragg reflectors (DBRs) was also carried out by using the obtained thermo-optic coefficients. It revealed that 9 nm red-shift can be obtained from room temperature to 500°C.

DOI： 10.1117/12.874531

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