研究者詳細 - 須田　淳

論文 - 須田　淳

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Effects of Dosage Increase on Electrical Properties of Metal-Oxide-Semiconductor Diodes with Mg-Ion-Implanted GaN Before Activation Annealing Open Access

Akazawa, M; Kamoshida, R; Murai, S; Narita, T; Omori, M; Suda, J; Kachi, T

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 257 巻 ( 2 ) 2020年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physica Status Solidi (B) Basic Research

The effect of increasing the dosage on the electrical properties of Mg-ion-implanted GaN before activation annealing is investigated to obtain knowledge on the defect levels generated by ion implantation. To probe the near-surface region, GaN metal-oxide-semiconductor (MOS) structures with Al2O3 are used. Two kinds of MOS diodes with Mg-ion dosages of 1.5 × 1011 and 1.5 × 1012 cm−2 implanted at 50 keV are prepared. Although anomalous capacitance–voltage (C–V) characteristics are observed for the low-dosage sample, they are improved by annealing at 600 °C for 3 h. However, for the high-dosage sample, more severe and persistent frequency dispersion is observed in the C–V characteristics, which is not improved by the same annealing. On the basis of the detailed analysis of capacitance–frequency (C–f) characteristics, it is concluded that the discrete interface trap at 0.2–0.3 eV below the conduction band is responsible for the frequency dispersion observed for the high-dosage sample. Combined with the results of deep-level transient spectroscopy, it is highly likely that the bulk deep levels affect the C–V and C–f characteristics. The possibility that the dominant deep levels are changed by the increase in Mg-ion dosage is discussed.

DOI： 10.1002/pssb.201900367

Overview of carrier compensation in GaN layers grown by MOVPE: toward the application of vertical power devices

Narita, T; Tomita, K; Kataoka, K; Tokuda, Y; Kogiso, T; Yoshida, H; Ikarashi, N; Iwata, K; Nagao, M; Sawada, N; Horita, M; Suda, J; Kachi, T

JAPANESE JOURNAL OF APPLIED PHYSICS 59 巻 ( SA ) 2020年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Sources of carrier compensation in n-type and p-type GaN layers grown by metalorganic vapor phase epitaxy were quantitatively identified by a combination of Hall-effect analysis and deep level transient spectroscopy. For n-type GaN, we identified three electron compensation sources: Residual carbon atoms likely sitting on nitrogen sites (CN), an electron trap at the energy level of E C-0.6 eV (the E3 trap), and self-compensation appearing with increasing donor concentration. We showed that the CN also play a key role in hole compensation in p-type GaN by forming donor-like charged states. We also investigated the reduction of acceptor concentrations (N a) in highly Mg-doped GaN. Atomic-resolution scanning transmission electron microscopy revealed that electrically inactive Mg atoms of 3/2 atomic layers are segregated at the boundary of pyramidal inversion domains. The N a reduction can be explained by this Mg segregation.

DOI： 10.7567/1347-4065/ab4610

Reduction of plasma-induced damage in n-type GaN by multistep-bias etching in inductively coupled plasma reactive ion etching

Yamada, S; Omori, M; Sakurai, H; Osada, Y; Kamimura, R; Hashizume, T; Suda, J; Kachi, T

APPLIED PHYSICS EXPRESS 13 巻 ( 1 ) 2020年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Plasma-induced damage was reduced by multistep-bias etching that involved a stepwise decrease of the etching bias power (P bias) and subsequent annealing. The depth of damage at P bias = 60 W was determined to be 60 nm from the capacitance-voltage characteristics of Ni/Al2O3/etched-GaN metal-oxide-semiconductor diodes. The damaged layer was removed by subsequent etching at P bias = 5 W and 2.5 W. The residual and shallow damage induced by the low P bias was then recovered by subsequent annealing at 400 °C. The multistep-bias etching of inductively coupled plasma reactive ion etching was thus confirmed to be effective for achieving a high etching rate with low damage.

DOI： 10.7567/1882-0786/ab5ffe

Impacts of high temperature annealing above 1400 °C under N<sub>2</sub> overpressure to activate acceptors in Mg-implanted GaN

Sakurai, H; Narita, T; Hirukawa, K; Yamada, S; Koura, A; Kataoka, K; Horita, M; Ikarashi, N; Bockowski, M; Suda, J; Kachi, T

PROCEEDINGS OF THE 2020 32ND INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND ICS (ISPSD 2020) 頁： 321 - 324 2020年

Impact Ionization Coefficients in GaN Measured by Above- and Sub-E<inf>g</inf> Illuminations for p<sup>-</sup>/n<sup>+</sup> Junction

Maeda T., Narita T., Yamada S., Kachi T., Kimoto T., Horita M., Suda J.

Technical Digest - International Electron Devices Meeting, IEDM 2019-December 巻 2019年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Technical Digest - International Electron Devices Meeting, IEDM

We propose a novel method to extract impact ionization coefficients of electrons and holes using above-and sub-bandgap illuminations for a p-/n+ junction diode. For above-bandgap illumination, the light is absorbed near p-GaN surface. Then, generated minority carriers diffuse and reach the edge of the depletion layer, resulting in an electron-injected photocurrent. On the other hand, for sub-bandgap illumination, the light is selectively absorbed near the p-n junction interface by the Franz-Keldysh effect, resulting in a hole-injected photocurrent. The electron- and hole-initiated multiplication factors are obtained as the ratios of the measured photocurrents to the calculated unmultiplicated photocurrents. By analyzing the electron- and hole-initiated multiplication factors, the impact ionization coefficients of electrons and holes in GaN are extracted separately.

DOI： 10.1109/IEDM19573.2019.8993438

Electric-field-induced simultaneous diffusion of Mg and H in Mg-doped GaN prepared using ultra-high-pressure annealing

Narita, T; Sakurai, H; Bockowski, M; Kataoka, K; Suda, J; Kachi, T

APPLIED PHYSICS EXPRESS 12 巻 ( 11 ) 2019年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

To investigate Mg diffusion during ultra-high-pressure annealing, which activates Mg acceptors in GaN, GaN samples with p-n junctions prepared via epitaxial growth were annealed at 1573 K under 1 GPa. The profiles of Mg diffusion toward the underlying n-type layer cannot be explained by a simple diffusion model. We found that H atoms diffused along with Mg atoms. By considering the suppressed diffusion of positively charged interstitial H atoms due to the electric field in the depletion layer, we could better reproduce the Mg-H diffusion profiles, suggesting that H atoms play a key role in the Mg diffusion process.

DOI： 10.7567/1882-0786/ab4934

Demonstration of Conductivity Modulation in SiC Bipolar Junction Transistors With Reduced Base Spreading Resistance

Asada Satoshi, Suda Jun, Kimoto Tsunenobu

IEEE TRANSACTIONS ON ELECTRON DEVICES 66 巻 ( 11 ) 頁： 4870 - 4874 2019年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Transactions on Electron Devices

SiC bipolar junction transistors (BJTs) were fabricated based on the design criterion proposed in our previous study, which quantitatively proved the importance of decreasing a base spreading resistance. To reduce the base spreading resistance, Al+-implantation was performed in the parasitic base region. No negative influences due to the implantation damage on the current gain were confirmed when the implantation is performed sufficiently apart from the emitter mesa sidewall, the distance of which is longer than 3μ m. Since the fabricated BJTs satisfied the design criterion, clear conductivity modulation was achieved, resulting in a reduced collector-resistance, that is, 50% of the unipolar resistance. In addition, we experimentally demonstrated that the conductivity modulation in SiC BJTs could be enhanced by decreasing the base spreading resistance.

DOI： 10.1109/TED.2019.2941884

Measurement of avalanche multiplication utilizing Franz-Keldysh effect in GaN p-n junction diodes with double-side-depleted shallow bevel termination

Maeda, T; Narita, T; Ueda, H; Kanechika, M; Uesugi, T; Kachi, T; Kimoto, T; Horita, M; Suda, J

APPLIED PHYSICS LETTERS 115 巻 ( 14 ) 2019年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Avalanche multiplication characteristics of GaN p-n junction diodes (PNDs) with double-side-depleted shallow bevel termination, which exhibit nearly ideal avalanche breakdown, were investigated by photomultiplication measurements using sub-bandgap light. In GaN PNDs under reverse bias conditions, optical absorption induced by the Franz-Keldysh (FK) effect is observed, resulting in a predictable photocurrent. The avalanche multiplication factors were extracted as a ratio of the measured values to the calculated FK-induced photocurrent. In addition, the temperature dependences of the avalanche multiplications were also investigated.

DOI： 10.1063/1.5114844

Highly effective activation of Mg-implanted p-type GaN by ultra-high-pressure annealing

Sakurai, H; Omori, M; Yamada, S; Furukawa, Y; Suzuki, H; Narita, T; Kataoka, K; Horita, M; Bockowski, M; Suda, J; Kachi, T

APPLIED PHYSICS LETTERS 115 巻 ( 14 ) 2019年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

A high activation ratio of acceptors to Mg ions implanted into a homoepitaxial GaN layer was achieved through an ultra-high-pressure annealing (UHPA) process. Capless annealing under a nitrogen pressure of 1 GPa in a temperature range of 1573-1753 K activated acceptors without thermally decomposing the GaN layer. Conventional rapid thermal annealing leads to a serious decomposition at 1573 K, even with an AlN protective cap. The sample annealed at 1673 K under UHPA exhibited very intense cathodoluminescence in near-band edge and donor-acceptor-pair band emissions. The intensities were over one order of magnitude higher than those of the sample treated by conventional annealing. A Hall-effect measurement was obtained in the temperature range of 275-500 K for the UHPA sample. The obtained hole concentration and mobility at 300 K were 3.6 × 1016 cm-3 and 24.1 cm2 V-1 s-1, respectively. The mobility value was close to that of an epitaxial p-type GaN with the same doping concentration. An Arrhenius plot of hole concentrations showed that the acceptor concentration and ionization energy were separately estimated to be (2.6 ± 0.8) × 1018 cm-3 and 212 ± 5 meV, respectively. By comparing the Mg concentrations obtained from secondary ion mass spectrometry, the acceptor activation ratio (acceptor concentration/Mg concentration) of the UHPA samples exceeded 70%. These results suggest that the UHPA process as a postimplantation annealing technique is promising for the fabrication of GaN-based power devices with selective area doping.

DOI： 10.1063/1.5116866

Franz-Keldysh effect in 4H-SiC p-n junction diodes under high electric field along the ⟨11(2)over-bar0⟩ direction

Maeda, T; Chi, XL; Tanaka, H; Horita, M; Suda, J; Kimoto, T

JAPANESE JOURNAL OF APPLIED PHYSICS 58 巻 ( 9 ) 2019年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Electric-field dependence of optical absorption induced by Franz-Keldysh (FK) effect strongly depends on the value of the reduced effective mass along electric field. In this study, reverse current-voltage characteristics of 4H-SiC{1120} p-n junction diodes under sub-bandgap illumination were investigated. Under a reverse bias condition, a photocurrent induced by FK effect was observed and increased with the reverse voltage. We calculated a photocurrent with consideration of phonon-assisted optical absorption induced by FK effect in a depletion region using the reduced effective mass perpendicular to the c-axis (μ⊥ = 0.26 m0), and the calculated values showed good agreement with the experimental values. This result indicates that the anisotropy of optical absorption induced by FK effect in 4H-SiC is small, since the reduced effective mass perpendicular to the c-axis (μ⊥ = 0.26 m0) is close to that parallel to the c-axis (μ∥ m = 0.28 m0).

DOI： 10.7567/1347-4065/ab3873

Deep-level transient spectroscopy studies of electron and hole traps in n-type GaN homoepitaxial layers grown by quartz-free hydride-vapor-phase epitaxy

Kanegae, K; Fujikura, H; Otoki, Y; Konno, T; Yoshida, T; Horita, M; Kimoto, T; Suda, J

APPLIED PHYSICS LETTERS 115 巻 ( 1 ) 2019年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

We studied deep levels in quartz-free hydride-vapor-phase epitaxy (QF-HVPE)-grown homoepitaxial n-type GaN layers within which three electron and eight hole traps were detected. The dominant electron and hole traps observed in the QF-HVPE-grown GaN layers were E3 (EC - 0.60 eV) and H1 (EV + 0.87 eV), respectively. We found that the E3 trap density of QF-HVPE-grown GaN (∼1014 cm-3) was comparable with that of MOVPE-grown GaN layers, whereas the H1 trap density of QF-HVPE-grown GaN (∼1014 cm-3) was much smaller than that of an MOVPE-grown GaN layer with a low-residual-carbon growth condition. A detailed analysis of the QF-HVPE-grown GaN layers revealed that the H1 trap density is almost equal to the carbon impurity concentration and other impurities that compensate the Si donors besides the carbon impurity were hardly detected in the QF-HVPE-grown GaN layers.

DOI： 10.1063/1.5098965

Shockley-Read-Hall lifetime in homoepitaxial p-GaN extracted from recombination current in GaN p-n<SUP>+</SUP> junction diodes Open Access

Maeda, T; Narita, T; Ueda, H; Kanechika, M; Uesugi, T; Kachi, T; Kimoto, T; Horita, M; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS 58 巻 ( SC ) 2019年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

The Shockley-Read-Hall (SRH) lifetime in homoepitaxial p-GaN (N a = 1 × 1017 cm-3) is investigated by analyzing forward current-voltage (I-V) characteristics in GaN-on-GaN p-n+ junction diodes with mesa-isolation structure. The ideality factor around 2 due to recombination current was obtained in the 1.8-2.7 V window, which is different from the characteristic of a p+-n- junction involving considerable diffusion current. The recombination current was proportional to the junction area, indicating that the recombination current is a bulk component, not a mesa-surface component. Analyzing the recombination current with consideration of the SRH recombination rate in the depletion layer, we obtained an SRH lifetime of 46 ps at 298 K. The temperature dependence of the I-V characteristics was also investigated and the SRH lifetimes were extracted in the range of 223-573 K. The SRH lifetime in homoepitaxial p-GaN followed the empirical power law of = 1.2 × 10-16 × T 2.25 (s).

DOI： 10.7567/1347-4065/ab07ad

Frontiers of Nitride Semiconductor Research FOREWORD

Chichibu, SF; Kumagai, Y; Kojima, K; Deura, M; Akiyama, T; Arita, M; Fujioka, H; Fujiwara, Y; Hara, N; Hashizume, T; Hirayama, H; Holmes, M; Honda, Y; Imura, M; Ishii, R; Ishitani, Y; Iwaya, M; Kamiyama, S; Kangawa, Y; Katayama, R; Kawakami, Y; Kawamura, T; Kobayashi, A; Kuzuhara, M; Matsumoto, K; Mori, Y; Mukai, T; Murakami, H; Murotani, H; Nakazawa, S; Okada, N; Saito, Y; Sakai, A; Sekiguchi, H; Shiozaki, K; Shojiki, K; Suda, J; Takeuchi, T; Tanikawa, T; Tatebayashi, J; Tomiya, S; Yamada, Y

JAPANESE JOURNAL OF APPLIED PHYSICS 58 巻 2019年6月

Design and Fabrication of GaN p-n Junction Diodes With Negative Beveled-Mesa Termination

Maeda, T; Narita, T; Ueda, H; Kanechika, M; Uesugi, T; Kachi, T; Kimoto, T; Horita, M; Suda, J

IEEE ELECTRON DEVICE LETTERS 40 巻 ( 6 ) 頁： 941 - 944 2019年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Electron Device Letters

We report on homoepitaxial GaN p-n junction diodes with a negative beveled-mesa termination. The electric field distribution in a beveled-mesa was investigated using TCAD simulation, and the devices were designed using currently available GaN growth techniques. Shallow-angle (ca. 10°) negative bevel GaN p-n junction diodes were fabricated with various Mg acceptor concentrations in the p-layers. The suppression of electric field crowding and improvement of the breakdown voltage were observed, as the Mg concentration was decreased. The parallel-plane breakdown field of 2.86 MV/cm was obtained for a device with the breakdown voltage of 425 V.

DOI： 10.1109/LED.2019.2912395

Process Technologies for GaN High Voltage Devices

Kachi T., Narita T., Sakurai H., Suda J.

Device Research Conference - Conference Digest, DRC 2019-June 巻頁： 235 - 236 2019年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Device Research Conference - Conference Digest, DRC

The vertical structure of the power device has advantages such as small chip size, easy wiring, and high breakdown voltage. Furthermore, wideband gap semiconductors have the greatest feature of low on-resistance. GaN is a material having the ability to fully exhibit these properties and in recent years development of GaN vertical devices has been accelerated. For example, GaN vertical devices with over lkV breakdown voltage have been reported recently1-5). Moreover, over 3kV pn diodes were also reported6,7). Therefore, ability of GaN for high voltage devices has been proven. Next issues are developments of fabrication process technologies which make devices stable operation. In this paper, we will report recent advances in process technology for GaN vertical devices.

DOI： 10.1109/DRC46940.2019.9046467

Estimation of Impact Ionization Coefficient in GaN by Photomulitiplication Measurement Utilizing Franz-Keldysh Effect

Maeda T., Narita T., Ueda H., Kanechika M., Uesugi T., Kachi T., Kimoto T., Horita M., Suda J.

Proceedings of the International Symposium on Power Semiconductor Devices and ICs 2019-May 巻頁： 59 - 62 2019年5月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Proceedings of the International Symposium on Power Semiconductor Devices and ICs

A valanche multiplication characteristics in GaN p-n junction diodes (PNDs) under high reverse bias conditions were investigated. The GaN-on-GaN PNDs with double-side-depleted shallow bevel termination, which showed low reverse leakage current and excellent avalanche capability, were used for the measurements. Under sub-bandgap light illumination, the photocurrents induced by Franz-Keldysh (FK) effect, which can be well reproduced by the theoretical calculations of the optical absorption, and their avalanche multiplications were observed. The multiplication factors were extracted as the ratios of the experimental photocurrents to the calculated FK-induced photocurrent. Under an assumption of equal impact ionization coefficients of electrons and holes, the electric-field dependence of an impact ionization coefficient in GaN were estimated.

DOI： 10.1109/ISPSD.2019.8757676

Parallel-Plane Breakdown Fields of 2.8-3.5 MV/cm in GaN-on-GaN p-n Junction Diodes with Double-Side-Depleted Shallow Bevel Termination

Maeda T., Narita T., Ueda H., Kanechika M., Uesugi T., Kachi T., Kimoto T., Horita M., Suda J.

Technical Digest - International Electron Devices Meeting, IEDM 2018-December 巻頁： 30.1.1 - 30.1.4 2019年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Technical Digest - International Electron Devices Meeting, IEDM

We report homoepitaxial GaN p-n junction diodes with novel beveled-mesa structures. The n-layers and p-layers, the doping concentrations of which are comparable, were prepared. We found that electric field crowding does not occur in the structure using TCAD simulation. The fabricated devices showed the breakdown voltages of 180-480 V, small leakage currents, and excellent avalanche capabilities. The breakdown voltages increased at elevated temperature. At the breakdown, nearly uniform luminescence in the entire p-n junctions was observed in all the devices. These results are strong evidences that the uniform avalanche breakdowns occurred in the devices. We carefully characterized the depletion layer width at the breakdown, and the parallel-plane breakdown electric fields of 2.8-3.5 MV/cm were obtained, which are among the best of the reported non-punch-through GaN vertical devices.

DOI： 10.1109/IEDM.2018.8614669

Estimation of Impact Ionization Coefficient in GaN by Photomulitiplication Measurement Utilizing Franz-Keldysh Effect

Maeda Takuya, Narita Tetsuo, Ueda Hiroyuki, Kanechika Masakazu, Uesugi Tsutomu, Kachi Tetsu, Kimoto Tsunenobu, Horita Masahiro, Suda Jun

2019 31ST INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES AND ICS (ISPSD) 頁： 59 - 62 2019年

Impact Ionization Coefficients in GaN Measured by Above- and Sub-<i>E</i><sub>g</sub> Illuminations for p<SUP>-</SUP>/n<SUP>+</SUP> Junction

Maeda, T; Narita, T; Yamada, S; Kachi, T; Kimoto, T; Horita, M; Suda, J

2019 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM) 2019年

Acceptors activation of Mg-ion implanted GaN by ultra-high-pressure annealing

Sakurai, H; Omori, M; Yamada, S; Koura, A; Suzuki, H; Narita, T; Kataoka, K; Horita, M; Kowski, MB; Suda, J; Kachi, T

2019 NINETEENTH INTERNATIONAL WORKSHOP ON JUNCTION TECHNOLOGY (IWJT) 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：19th International Workshop on Junction Technology, IWJT 2019

For the solution to global energy issues, highly-efficient energy conversion using next-generation power devices is required. Gallium nitride (GaN) having superior properties such as high breakdown electric field (2.8-3.75 MV/cm) is a powerful candidate for next-generation high-power semiconductor devices. [1] , [2] The selective area doping makes it possible to precisely engineer high-power devices with complex structures, allowing formation of low-resistivity region for contacting electrodes and optimization of the electric field configuration in the edge termination represented by the field limiting ring (FLR) and in the junction barrier Schottky (JBS) structures, as used in Si and SiC power devices.

DOI： 10.23919/iwjt.2019.8802621

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