研究者詳細 - 堀田　昌宏

論文 - 堀田　昌宏

分割表示 >> ／全件表示 55 件中 1 - 55 件目

Nitrogen-displacement-related recombination centers generated by electron beam irradiation in n-type and p-type homoepitaxial GaN layers 査読有り

Endo, M; Horita, M; Suda, J

APPLIED PHYSICS EXPRESS 17 巻 ( 1 ) 2024年1月

記述言語：英語出版者・発行元：Applied Physics Express

Recombination centers originating from point defects generated by the displacement of N atoms in n-type and p-type GaN were investigated by analyzing Shockley-Read-Hall (SRH) recombination currents in homoepitaxial GaN p-n junctions. These defects were intentionally generated by electron beam (EB) irradiation at 137 keV. The net doping concentrations in p+-n junction diodes were not changed following irradiation although the levels in p-n+ junction diodes decreased as the EB fluence was increased. The SRH recombination current also increased with increases in the fluence. This work additionally evaluated the relationship between recombination lifetimes and trap concentrations obtained by deep level transient spectroscopy.

DOI： 10.35848/1882-0786/ad16ad

High Hall electron mobility in the inversion layer of 4H-SiC (0001)/SiO<sub>2</sub> interfaces annealed in POCl<sub>3</sub> 査読有り

Ito, K; Horita, M; Suda, J; Kimoto, T

APPLIED PHYSICS EXPRESS 16 巻 ( 7 ) 2023年7月

記述言語：英語出版者・発行元：Applied Physics Express

Hall effect measurements were conducted for MOSFETs with and without post-oxidation-annealing (POA) fabricated on the p-body doping in a wide doping range to vary the effective normal field (E eff). The Hall mobility (μ Hall) in the high-E eff region of the MOSFETs annealed in phosphoryl chloride (μ Hall = 41 cm2 V−1 s−1 at E eff = 1.1 MV cm−1) is much higher than that of MOSFETs annealed in nitric oxide (NO) (μ Hall = 14 cm2 V−1 s−1 at E eff = 1.1 MV cm−1), suggesting that the trapped electrons act as strong Coulomb scattering centers for the MOSFETs annealed in NO and without POA.

DOI： 10.35848/1882-0786/ace150

Correlation between non-ionizing energy loss and production rate of electron trap at <i>E</i><sub>C</sub> - (0.12-0.20) eV formed in gallium nitride by various types of radiation 査読有り

Aoshima, K; Horita, M; Suda, J

APPLIED PHYSICS LETTERS 122 巻 ( 1 ) 2023年1月

記述言語：英語出版者・発行元：Applied Physics Letters

Production rate (PR = trap concentration/incident fluence) of traps formed by energetic particles is important for predicting device degradation caused by radiation when developing radiation-resistant devices. We demonstrate a clear correlation between non-ionizing energy loss (NIEL) and PR of an electron trap at about 0.12-0.20 eV below the conduction band edge [EC - (0.12-0.20) eV] for various types of energetic particles in gallium nitride (GaN). NIEL values in GaN for electrons, protons, and α-rays were calculated using a screened-relativistic treatment, and NIEL values for gamma-rays were calculated by simulating slowed-down spectra due to shielding material. To obtain the PRs of the electron trap, 60Co gamma-rays with an average photon energy of 1.25 MeV and electron beams with energies from 137 keV to 2 MeV were irradiated onto n-type GaN Schottky barrier diodes. We measured the concentration of an electron trap at EC - (0.13-0.14) eV using deep-level transient spectroscopy. We also used the PRs of electron traps with similar energy levels of EC - (0.12-0.20) eV from previous studies on electrons, protons, and α-rays irradiated on GaN. All the trap PRs were proportional to the NIEL in a range of eight orders of magnitude, which confirms that the energy levels formed by various energetic particles have the same origin of being generated by atomic displacements. The obtained relationship coefficient between the NIEL and PRs of the trap is useful for predicting the degradation of GaN-based devices due to traps formed by various kinds of radiation.

DOI： 10.1063/5.0128709

Polarization Engineering in AlSiO/p-type GaN MOSFETs Using AIN Interlayers Formed by Plasma-Enhanced Atomic Layer Deposition 査読有り

Ito K., Narita T., Iguchi H., Iwasaki S., Kikuta D., Kano E., Ikarashi N., Tomita K., Horita M., Suda J.

Technical Digest - International Electron Devices Meeting, IEDM 2023年

記述言語：英語出版者・発行元：Technical Digest - International Electron Devices Meeting, IEDM

Polarization engineering by AIN interlayers (AlN-ILs) deposited via plasma-enhanced atomic layer deposition was demonstrated in AlSiO/p-type GaN MOSFETs. Transmission electron microscopy observations revealed that the AlN-ILs were grown on GaN epitaxially and therefore could induce polarization charges, similar to AlGaN/GaN. The decrease in the threshold voltage (Vth) with increasing AIN-IL thickness corresponded to the polarization charge density. In addition, insertion of the AIN-IL suppressed the positive bias instability by less than 0.05 V. By controlling the AIN-IL thickness and the channel p-type doping, we controlled the Vth the range from -3 to 5 V and achieved enhanced channel mobility compared with that for the corresponding MOSFET without an AIN-IL.

DOI： 10.1109/IEDM45741.2023.10413714

Depth profiling of E <inf>C</inf> - 0.26 eV electron traps introduced in homoepitaxial n-type GaN by ultra-low-dose Si-ion implantation and subsequent annealing 査読有り

Iguchi H., Horita M., Suda J.

Applied Physics Express 15 巻 ( 12 ) 2022年12月

記述言語：英語出版者・発行元：Applied Physics Express

Si ions were implanted into homoepitaxial n-type GaN at a peak concentration of 3 × 1014 cm−3 with subsequent annealing, and the associated formation of electron traps was investigated in detail using deep-level transient spectroscopy. A major electron trap was identified as 0.26 eV below the conduction band minimum and this trap concentration increased with increasing post-implantation annealing temperature, to a value of 6-8 × 1015 cm−3. Significant increases in the net donor concentration (N D) were also observed within the implanted region. The profile of the electron trap concentration was correlated with these increases in N D, suggesting that these traps acted as donors.

DOI： 10.35848/1882-0786/aca45d

Process engineering of GaN power devices via selective-area p-type doping with ion implantation and ultra-high-pressure annealing 査読有り

Kachi, T; Narita, T; Sakurai, H; Matys, M; Kataoka, K; Hirukawa, K; Sumida, K; Horita, M; Ikarashi, N; Sierakowski, K; Bockowski, M; Suda, J

JOURNAL OF APPLIED PHYSICS 132 巻 ( 13 ) 2022年10月

記述言語：英語出版者・発行元：Journal of Applied Physics

P-type doping in selected areas of gallium nitride (GaN) using magnesium (Mg)-ion implantation and subsequent ultra-high-pressure annealing (UHPA) are investigated to improve the performance of vertical GaN power devices. UHPA allows a high-temperature process without decomposition of the GaN surface and virtually complete activation of the implanted Mg ions in GaN. In the present paper, we provide an overview of recent challenges in making UHPA more realistic as an industrial process. Instead of UHPA at more than 1400 °C for a short duration, prolonged UHPA at 1300 °C demonstrates a comparable acceptor activation of Mg-ion-implanted GaN. This can reduce the annealing pressure to approximately 300 MPa and enlarge the processable wafer diameter. The second challenge is controlling the doping profiles in the lateral and vertical directions. We demonstrate fine patterning of the p-type regions, which indicates the limited lateral diffusion of Mg through UHPA. However, controlling the vertical doping profile is challenging. The nitrogen vacancies formed by ion implantation reduce the effective acceptor concentration near the surface, which can be compensated for by sequential nitrogen ion implantation. Defect-assisted Mg diffusion to the deeper region causes a redistribution of the Mg atoms and should be considered in the design of a device. Such anisotropic diffusion of Mg to the c-axis has potential applications in the fabrication of unique vertical device structures such as super junctions.

DOI： 10.1063/5.0107921

Effective channel mobility in phosphorus-treated 4H-SiC (0001) metal-oxide-semiconductor field-effect transistors with various p-body doping concentrations 査読有り

Ito, K; Horita, M; Suda, J; Kimoto, T

JAPANESE JOURNAL OF APPLIED PHYSICS 61 巻 ( 9 ) 2022年9月

記述言語：英語出版者・発行元：Japanese Journal of Applied Physics

Phosphorus treatment, which can substantially reduce the interface state density (D it), was used to investigate the impact of D it on effective channel mobility (μ eff) of 4H-SiC (0001) metal-oxide-semiconductor field-effect transistors (MOSFETs). A high μ eff of 126 cm2 V-1 s-1, which exceeds the reported phonon-limited mobility of 83 cm2 V-1 s-1 determined from Hall mobility of nitridation-treated MOSFETs, at a high effective normal field of 0.57 MV cm-1 was obtained in MOSFETs fabricated on a high-purity semi-insulating 4H-SiC substrate at room temperature. This high mobility may be caused by the difference of the density of electrons trapped at the interface states.

DOI： 10.35848/1347-4065/ac87e4

Increase in net donor concentration due to introduction of donor-like defects by ultra-low-dose Si-ion implantation and subsequent annealing in homoepitaxial n-type GaN 査読有り

Iguchi, H; Horita, M; Suda, J

APPLIED PHYSICS EXPRESS 15 巻 ( 7 ) 2022年7月

記述言語：英語出版者・発行元：Applied Physics Express

Si ions were implanted at a dose of 1 × 1010 cm-2 into a homoepitaxial n-type GaN layer with a net donor concentration (N D) of 3-8 × 1015 cm-3. The N D in the implanted region increased by 1-3 × 1015 cm-3 after annealing at a temperature greater than 900 °C compared with that for the as-grown homoepitaxial layer. The increase in N D was considerably larger than the peak concentration of implanted Si ions (3 × 1014 cm-3). No increase in N D was observed for an as-grown sample after annealing. These results clearly suggest that donor-like defects were introduced by implantation of Si ions and a subsequent annealing process.

DOI： 10.35848/1882-0786/ac7433

SiO<sub>2</sub>/GaN interfaces with low defect densities and high breakdown electric fields formed by plasma-enhanced atomic layer deposition 査読有り

Aoshima, K; Taoka, N; Horita, M; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS 61 巻 ( SC ) 2022年5月

記述言語：英語出版者・発行元：Japanese Journal of Applied Physics

We present SiO2/GaN interfaces with a low interface state density and a high breakdown electric field. The SiO2 films were deposited by plasma-enhanced atomic layer deposition (ALD) using bis(diethylamino)silane and O2 plasma at 300 °C on n-type GaN (0001) homoepitaxial layers. An interface state density of less than 1011 cm-2 eV-1 at 0.3 eV below the conduction band edge was confirmed by the conductance method. The value is much lower than those of previously reported ALD-SiO2/GaN interfaces (1012-1013 cm-2 eV-1). A low fixed charge density at the SiO2/GaN interface of 3.7 × 1011 cm-2 and a high dielectric breakdown field of ∼10 MV cm-1 were obtained. Moreover, the interface state density and current-voltage characteristics were further improved by post-deposition annealing at 400 °C in N2 ambient. Scanning transmission electron microscopy with energy-dispersive X-ray analysis revealed the existence of a GaO x interlayer between SiO2 and GaN. The unintentionally formed interlayer could be one of the reasons for the improvement of interface properties at ALD-SiO2/GaN.

DOI： 10.35848/1347-4065/ac4f79

Hole traps related to nitrogen displacement in p-type GaN grown by metalorganic vapor phase epitaxy on freestanding GaN 査読有り

Endo, M; Horita, M; Suda, J

APPLIED PHYSICS LETTERS 120 巻 ( 14 ) 2022年4月

記述言語：英語出版者・発行元：Applied Physics Letters

This work investigated deep levels in p-type GaN originating from intrinsic point defects, using deep level transient spectroscopy (DLTS) to examine homoepitaxial GaN p+-p-n+ junction diodes grown via metalorganic vapor-phase epitaxy. Following exposure to an electron beam with an energy of 137 keV that generated nitrogen vacancies (VN) and nitrogen interstitials (NI), a peak due to EHa hole traps (at 0.52 eV) was observed in DLTS spectra. The injection of minority carriers resulting from applying a forward bias generated signals for EHb (0.5 eV) and EHc (0.8 eV) hole traps while decreasing the EHa signal and increasing the net accepter concentration. The generation of EHa traps can likely be attributed to VN (3+/+) or NI (2+/+) defects based on the results of first-principles calculations. The EHb and EHc hole traps may have been associated with complex defects, including those that generated EHa traps, because these two traps appeared as the concentration of EHa traps decreased.

DOI： 10.1063/5.0086535

Breakdown Electric Field of GaN p<SUP>+</SUP>-n and p-n<SUP>+</SUP> Junction Diodes With Various Doping Concentrations 査読有り

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

IEEE ELECTRON DEVICE LETTERS 43 巻 ( 1 ) 頁： 96 - 99 2022年1月

記述言語：英語出版者・発行元：IEEE Electron Device Letters

Breakdown characteristics in homoepitaxial GaN p-n junction diodes with p+-n and p-n+ junctions with relatively heavy doping concentrations are systematically investigated. The devices have vertical deep mesa etch termination, which enables uniform (nearly ideal) avalanche breakdown without electric field (E-field) crowding at the device edge. For p+-n junction, breakdown E-field of 3.0, 3.3 and 3.8 MV/cm and breakdown voltage (BV) of 340, 207 and 128 V were achieved at the donor concentrations of 7.5 × 1016, 1.5 × 1017, 3.1× 1017 cm-3, respectively. For p-n+ junction, breakdown E-field of 3.2, 3.3 and 4.0 MV/cm and BV of 235, 180 and 110 V were achieved at the acceptor concentrations of 1.3 × 1017, 1.8 × 1017, 4.1 × 1017 cm-3, respectively. No significant difference of the breakdown characteristics between n-type and p-type voltage-blocking layers was observed. These results are consistent with numerical simulations using impact ionization coefficients (IICs) in GaN reported in our previous studies.

DOI： 10.1109/LED.2021.3125328

Effect of annealing time and pressure on electrical activation and surface morphology of Mg-implanted GaN annealed at 1300 °C in ultra-high-pressure nitrogen ambient 査読有り

Sumida, K; Hirukawa, K; Sakurai, H; Sierakowski, K; Horita, M; Bockowski, M; Kachi, T; Suda, J

APPLIED PHYSICS EXPRESS 14 巻 ( 12 ) 2021年12月

記述言語：英語出版者・発行元：Applied Physics Express

We performed an isothermal annealing study on Mg-implanted GaN at 1300 °C in an ultra-high-pressure (1 GPa) nitrogen ambient. Annealing for more than 30 min resulted in a high acceptor activation ratio and a low compensation ratio that were comparable to those obtained with annealing at 1400 °C for 5 min. We also performed annealing at 1300 °C in a reduced nitrogen pressure of 300 MPa which makes us possible to expand the inner diameter of annealing equipment in the future. High electrical activation, similar to one obtained by annealing at 1 GPa, was successfully obtained.

DOI： 10.35848/1882-0786/ac39b0

Effect of Schottky barrier height on quantitative analysis of deep-levels in n-type GaN by deep-level transient spectroscopy 査読有り

Aoshima, K; Horita, M; Suda, J

AIP ADVANCES 11 巻 ( 11 ) 2021年11月

記述言語：英語出版者・発行元：AIP Advances

Deep-level transient spectroscopy (DLTS) using Schottky barrier diodes (SBDs) is widely used for quantitative analysis of deep levels. This study focuses on the dependence of Schottky barrier height on apparent time constants and concentrations of electron traps in n-type GaN. DLTS using SBDs with various barrier heights was carried out. Experimental data show that large reverse leakage currents due to low barrier heights resulted in underestimation of time constants and concentrations. Theoretical calculations considering the impact of leakage currents reproduced experimental results well. Based on the calculations, we suggest a minimum required barrier height where accurate time constants and concentrations can be evaluated.

DOI： 10.1063/5.0073747

Effects of the sequential implantation of Mg and N ions into GaN for p-type doping 査読有り

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

APPLIED PHYSICS EXPRESS 14 巻 ( 11 ) 2021年11月

記述言語：英語出版者・発行元：Applied Physics Express

The sequential implantation of Mg and N ions into GaN was investigated using conventional rapid thermal annealing and ultra-high-pressure annealing (UHPA). In cathodoluminescence, the green luminescence related to nitrogen vacancies (VNs) was mostly suppressed at the Mg/N ratio of 0.5-1.0, whereas the donor-acceptor pair (DAP) emission as a signature of Mg acceptors was maintained high. The excess N implantation reduced the DAP emission through the formation of nonradiative recombination centers. The combined process of optimal Mg/N implantation and UHPA at 1673 K improved ohmic contacts by increasing Mg concentration and suppressing VNs near the surface.

DOI： 10.35848/1882-0786/ac2ae7

GaN縦型パワーデバイス実現に向けた点欠陥評価査読有り

須田淳, 堀田昌宏, 鐘ヶ江一孝

応用物理 90 巻 ( 10 ) 頁： 628 - 631 2021年10月

記述言語：日本語出版者・発行元：公益社団法人応用物理学会

<p>GaN縦型パワーデバイスのエピタキシャル成長，デバイスプロセスの開発，あるいは，デバイス設計に点欠陥の知見は不可欠であるが，SiやGaAsに比べると，GaNの点欠陥の理解はまだまだ不足している．議論が分かれていた電子トラップの起源特定，n型GaN中の正孔トラップの簡便な定量評価方法の開発や測定の高速化によるウェーハマッピング，電子線照射により意図的に窒素原子のみを変位させることにより，窒素空孔や格子間窒素の作るトラップ準位，アニール挙動など，筆者らが取り組んできた研究について紹介する．</p>

DOI： 10.11470/oubutsu.90.10_628

Depth profiles of electron traps generated during reactive ion etching in n-type 4H-SiC characterized by using isothermal capacitance transient spectroscopy 査読有り

Kanegae, K; Okuda, T; Horita, M; Suda, J; Kimoto, T

JOURNAL OF APPLIED PHYSICS 130 巻 ( 10 ) 2021年9月

記述言語：英語出版者・発行元：Journal of Applied Physics

Electron traps generated during the reactive ion etching (RIE) process in n-type 4H-SiC are investigated using the deep-level transient spectroscopy technique and isothermal capacitance transient spectroscopy (ICTS) technique. Two electron traps of the Z1/2 center are detected in the RIE-etched sample by ICTS measurement at 300 K. A method is proposed to determine the depth profiles of the electron traps that are localized near the etched surface, whereby a depth profile is extracted from the dependence of averaged trap density on the depletion layer width. An exponential distribution is assumed as the depth profile of the electron traps generated during the RIE process. The extracted depth profile was confirmed to be consistent with that determined by the double-correlation method. An appropriate function for the depth profile of carrier traps is assumed and the dependence of the averaged trap density on the depletion layer width is analyzed, which enables the extraction of a depth profile that has both higher depth resolution and higher resolution in the carrier trap density with the proposed method than that with the double-correlation method.

DOI： 10.1063/5.0059588

Photoionization cross section ratio of nitrogen-site carbon in GaN under sub-bandgap-light irradiation determined by isothermal capacitance transient spectroscopy 査読有り

Kanegae, K; Narita, T; Tomita, K; Kachi, T; Horita, M; Kimoto, T; Suda, J

APPLIED PHYSICS EXPRESS 14 巻 ( 9 ) 2021年9月

記述言語：英語出版者・発行元：Applied Physics Express

The ratio of the photoionization cross sections (σo/n σ o/p) of carbon substituting at the nitrogen site [CN (0/-)] in n-type GaN, which is detected as a hole trap H1 (EV + 0.85 eV) under sub-bandgap-light irradiation (390 nm), is determined with isothermal capacitance transient spectroscopy (ICTS). The current-injection ICTS and the sub-bandgap-light-excited ICTS were compared for the same p+-n junction diode, whereby the hole occupancy ratio (fT) was obtained. Analysis of the dependence of fT on the temperature gave σo/n σ o/p of 3.0 was then used to estimate the charge state of CN (0/-) under sub-bandgap-light irradiation.

DOI： 10.35848/1882-0786/ac16ba

Impact ionization coefficients and critical electric field in GaN 査読有り

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

JOURNAL OF APPLIED PHYSICS 129 巻 ( 18 ) 2021年5月

記述言語：英語出版者・発行元：Journal of Applied Physics

Avalanche multiplication characteristics in a reverse-biased homoepitaxial GaN p-n junction diode are experimentally investigated at 223-373 K by novel photomultiplication measurements utilizing above- and below-bandgap illumination. The device has a non-punch-through one-side abrupt p--n+ junction structure, in which the depletion layer mainly extends to the p-type region. For above-bandgap illumination, the light is absorbed at the surface p+-layer, and the generated electrons diffuse and reach the depletion layer, resulting in an electron-injected photocurrent. On the other hand, for below-bandgap illumination, the light penetrates a GaN layer and is absorbed owing to the Franz-Keldysh effect in the high electric field region (near the p-n junction interface), resulting in a hole-induced photocurrent. The theoretical (non-multiplicated) photocurrents are calculated elaborately, and the electron- and hole-initiated multiplication factors are extracted as ratios of the experimental data to the calculated values. Through the mathematical analyses of the multiplication factors, the temperature dependences of the impact ionization coefficients of electrons and holes in GaN are extracted and formulated by the Okuto-Crowell model. The ideal breakdown voltage and the critical electric field for GaN p-n junctions of varying doping concentration are simulated using the obtained impact ionization coefficients, and their temperature dependence and conduction-type dependence were discussed. The simulated breakdown characteristics show good agreement with data reported previously, suggesting the high accuracy of the impact ionization coefficients obtained in this study.

DOI： 10.1063/5.0050793

Isochronal annealing study of Mg-implanted p-type GaN activated by ultra-high-pressure annealing 査読有り

Hirukawa, K; Sumida, K; Sakurai, H; Fujikura, H; Horita, M; Otoki, Y; Sierakowski, K; Bockowski, M; Kachi, T; Suda, J

APPLIED PHYSICS EXPRESS 14 巻 ( 5 ) 2021年5月

記述言語：英語出版者・発行元：Applied Physics Express

Isochronal annealing was performed on Mg-ion-implanted GaN under 1 GPa N2 ambient pressure for 5 min at temperatures of 1573-1753 K. Secondary ion mass spectrometry showed diffusion of Mg atoms and introduction of H atoms during annealing. Deeper diffusion was observed with increasing temperature. From Hall-effect measurements, p-type conductivity was found even for the sample with the lowest annealing temperature of 1573 K. For this sample, the acceptor activation ratio was 23% and the compensation ratio was 93%. The acceptor activation ratio increased to almost 100% and the compensation ratio decreased to 12% with increasing annealing temperature.

DOI： 10.35848/1882-0786/abf4f3

Analysis of channel mobility in GaN-based metal-oxide-semiconductor field-effect transistors 査読有り

Ito, K; Tomita, K; Kikuta, D; Horita, M; Narita, T

JOURNAL OF APPLIED PHYSICS 129 巻 ( 8 ) 2021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：Journal of Applied Physics

The factors limiting channel mobility in AlSiO/p-type GaN-based metal-oxide-semiconductor field-effect transistors (MOSFETs) were systematically investigated. MOSFETs with various thin interfacial layers (ILs) between Al0.78Si0.22Oy films and Mg-doped GaN layers were prepared and found to exhibit different channel mobilities. The maximum effective mobility showed a significant correlation with the threshold voltage (Vt) and the hysteresis (ΔVt) in the transfer characteristics of these devices, such that the mobility decreased with increasing Vt and ΔVt. This effect can be explained by electron capture in and emission from border traps situated near the conduction band minimum for GaN. The insertion of a 3-nm-thick SiO2 IL drastically enhanced the effective mobility and simultaneously reduced the ΔVt value. Hall effect measurements with an applied gate voltage were used to determine the mobility of free electrons while excluding electrons captured in the border traps. The Hall effect mobility was much higher than the effective mobility, indicating that mobility was in fact reduced by the capture of electrons by the border traps. The ratio of electrons captured by border traps to the overall electrons induced by a gate bias was greatly lowered in a MOSFET incorporating a SiO2 IL. When a high vertical electric field of approximately 1 MV/cm was present in the device channel, the Hall effect mobility was slightly increased following the insertion of an IL. These results suggest that the IL reduced the interfacial roughness and/or affected the screening out of scattering due to potential fluctuations of the AlSiO.

DOI： 10.1063/5.0040700

Nitrogen-displacement-related electron traps in <i>n</i>-type GaN grown on a GaN freestanding substrate 査読有り

Horita, M; Narita, T; Kachi, T; Suda, J

APPLIED PHYSICS LETTERS 118 巻 ( 1 ) 2021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 Letters

Energy levels due to intrinsic point defects are identified by deep-level transient spectroscopy (DLTS). Electron-beam (EB) irradiation created nitrogen vacancies (VN) and nitrogen interstitials (NI) in n-type GaN layers grown via metalorganic vapor phase epitaxy on freestanding GaN substrates, where the irradiation energies were selected to be within 100-401 keV to displace only nitrogen atoms in GaN. Two electron traps, EE1 (0.13 eV) and EE2 (0.98 eV), were observed in the DLTS spectra. The production rates of EE1 and EE2 were 0.093 and 0.109 cm-1 under 401 keV irradiation, which were nearly equal values. In the DLTS spectra recorded for EB-irradiated samples at the energy ranging from 100 to 401 keV, EE1 and EE2 were found to appear simultaneously at an irradiation energy of 137 keV and were observed at energies greater than 137 keV. On the basis of a comparison with the results of recent first-principles calculations, we attributed the EE1 and EE2 peaks to nitrogen vacancies VN (+/0) and nitrogen interstitials NI (0/-), respectively. Furthermore, annealing led to reductions of the densities of these traps at the same rate. The reduction of the densities of EE1 and EE2 can be explained by the migration of NI and the subsequent recombination with VN. The displacement energy of 21.8 eV for nitrogen in GaN was obtained from the irradiation-energy dependence of EE1.

DOI： 10.1063/5.0035235

Impact of gamma-ray irradiation on capacitance-voltage characteristics of Al<sub>2</sub>O<sub>3</sub>/GaN MOS diodes with and without post-metallization annealing 査読有り

Aoshima, K; Horita, M; Suda, J; Hashizume, T

APPLIED PHYSICS EXPRESS 14 巻 ( 1 ) 2021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

Atomic layer deposited Al2O3/GaN metal-oxide-semiconductor (MOS) diodes with and without post-metallization annealing (PMA) were irradiated with gamma-rays. Capacitance-voltage measurements were made before and after irradiation to investigate trap formation in Al2O3 films and interface states between Al2O3 and GaN. Negative flat-band voltage shifts were observed. The flat-band voltage shift depends on the Al2O3 thickness, showing different distributions of gamma-ray-induced positive charges for samples with and without PMA. The interface state density of the PMA sample slightly increased after irradiation, but was lower than that of the sample without PMA before irradiation.

DOI： 10.35848/1882-0786/abd71a

Space charge profile study of AlGaN-based p-type distributed polarization doped claddings without impurity doping for UV-C laser diodes 査読有り

Zhang, ZY; Kushimoto, M; Horita, M; Sugiyama, N; Schowalter, LJ; Sasaoka, C; Amano, H

APPLIED PHYSICS LETTERS 117 巻 ( 15 ) 2020年10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

The space charge density profile of the nondoped AlGaN-based p-type cladding layer for UV-C laser diodes realized by distributed polarization doping is examined theoretically and experimentally. The analysis of the capacitance-voltage measurement revealed that the average effective acceptor density of 4.2×1017 cm-3 is achieved even without impurity doping, and it is in good agreement with the theoretical prediction from the measured Al composition profile. This result suggests that the cladding layer is ideal for UV-C LDs because it provides sufficient hole injection while potentially avoiding internal losses due to impurity doping.

DOI： 10.1063/5.0027789

Why do electron traps at<i>E</i><sub>C</sub>-0.6 eV have inverse correlation with carbon concentrations in n-type GaN layers? 査読有り

Narita, T; Horita, M; Tomita, K; Kachi, T; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS 59 巻 ( 10 ) 2020年10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

We found that the graphite elements in a metalorganic vapor phase epitaxy reactor are a significant source of iron atoms, and lead to the formation of E3 electron traps at an energy E C-0.6 eV in n-type GaN layers. Thus, the previously reported inverse correlation between the E3 trap and carbon concentrations can be explained in terms of the correlation between the growth parameters. A high V/III ratio reduced carbon incorporation and simultaneously decreased the growth rate, resulting in increased iron incorporation in the layer grown. A high temperature also reduced carbon incorporation, while iron incorporation and the formation of E3 traps were both increased by enhanced etching of the graphite elements. By optimizing the growth conditions, we successfully suppressed both E3 trap formation and carbon incorporation in n-type GaN layers on 2 inch wafers.

DOI： 10.35848/1347-4065/abb9ca

Progress on and challenges of p-type formation for GaN power devices 査読有り

Narita, T; Yoshida, H; Tomita, K; Kataoka, K; Sakurai, H; Horita, M; Bockowski, M; Ikarashi, N; Suda, J; Kachi, T; Tokuda, Y

JOURNAL OF APPLIED PHYSICS 128 巻 ( 9 ) 2020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：Journal of Applied Physics

The fabrication processes of p-type regions for vertical GaN power devices are investigated. A p-type body layer in a trench gate metal-oxide-semiconductor field-effect transistor requires precise control of the effective acceptor concentration, which is equal to the difference between the Mg acceptor concentration (Na) and the compensating donor concentration (Nd). The carbon atoms incorporated during growth via metalorganic vapor phase epitaxy substitute nitrogen sites (CN) and function as donor sources in a p-type GaN layer. Since interstitial H atoms (H i) also compensate holes, their removal from an Mg-doped layer is crucial. Extended anneals to release H atoms cause the formation of extra hole traps. The p+ capping layer allows effective and rapid removal of H atoms from a p-type body layer owing to the electric field across the p+/p- junction. On the other hand, selective area p-type doping via Mg ion implantation is needed to control the electrical field distribution at the device edge. Ultrahigh-pressure annealing (UHPA) under a nitrogen pressure of 1 GPa enables post-implantation annealing up to 1753 K without thermal decomposition. Cathodoluminescence spectra and Hall-effect measurements suggest that the acceptor activation ratio improves dramatically by annealing above 1673 K as compared to annealing at up to 1573 K. High-temperature UHPA also induces Mg atom diffusion. We demonstrate that vacancy diffusion and the introduction of H atoms from the UHPA ambient play a key role in the redistribution of Mg atoms.

DOI： 10.1063/5.0022198

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

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 International Symposium on Power Semiconductor Devices and ICs 2020-September 巻頁： 321 - 324 2020年9月

記述言語：英語出版者・発行元：Proceedings of the International Symposium on Power Semiconductor Devices and ICs

In this study, we clarify the impact of annealing pressure and temperature of the ultra-high-pressure annealing (UHPA) as a post-implantation-annealing (PIA) on the acceptor activation for Mg-ions-implanted GaN samples. The pressure to prevent the thermal decomposition is absolutely determined by the equilibrium N2 partial pressure in the phase diagram of GaN-Ga-N2 system, so that the pressure below the critical pressure always leads to the serious surface decomposition of GaN. In low temperature cathodoluminescence examinations, the samples processed at 1400°C or above exhibited more intense emissions in the near band edge and donor-acceptor pair band with a suppression of green luminescence related to point defects. Temperature dependent Hall-effect measurement was allowed for the UHPA samples annealed at 1400°C or above, whereas free holes were not observed for the 1300°C-UHPA. Moreover, the acceptor concentrations (Na) for samples annealed at 1400°C or above were close to Mg concentrations. We thus revealed the key process parameters in UHPA, which is at more than 1400°C under the N2 overpressure exceeding the equilibrium partial pressure. These findings can play as a key role in the selective area doping using UHPA.

DOI： 10.1109/ISPSD46842.2020.9170174

Redistribution of Mg and H atoms in Mg-implanted GaN through ultra-high-pressure annealing 査読有り

Sakurai Hideki, Narita Tetsuo, Omori Masato, Yamada Shinji, Koura Akihiko, Iwinska Malgorzata, Kataoka Keita, Horita Masahiro, Ikarashi Nobuyuki, Bockowski Michal, Suda Jun, Kachi Tetsu

APPLIED PHYSICS EXPRESS 13 巻 ( 8 ) 2020年8月

Identification of origin ofE(C)-0.6 eV electron trap level by correlation with iron concentration in n-type GaN grown on GaN freestanding substrate by metalorganic vapor phase epitaxy 査読有り

Horita Masahiro, Narita Tetsuo, Kachi Tetsu, Suda Jun

APPLIED PHYSICS EXPRESS 13 巻 ( 7 ) 2020年7月

Dual-color-sub-bandgap-light-excited isothermal capacitance transient spectroscopy for quick measurement of carbon-related hole trap density in n-type GaN 査読有り

Kanegae K., Narita T., Tomita K., Kachi T., Horita M., Kimoto T., Suda J.

Japanese Journal of Applied Physics 59 巻 ( SG ) 2020年4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

A quick method is proposed for measurement of the carbon-related hole trap (H1: +0.87 eV) density in an n-type GaN homoepitaxial layer using dual-color-sub-bandgap-light-excited isothermal capacitance transient spectroscopy. Shorter wavelength (390 nm) light irradiation is employed to cause the hole traps to be in the hole-occupied state. Longer wavelength (660 nm) light irradiation is then used to emit the hole from the trap to the valence band. The photoemission of holes is much quicker than the thermal emission, which reduces the measurement time. The trap density can be calculated from the capacitance transient.

DOI： 10.35848/1347-4065/ab6863

Electron traps formed by gamma-ray irradiation in homoepitaxial <i>n</i>-type GaN and their annealing behavior 査読有り

Aoshima, K; Kanegae, K; Horita, M; Suda, J

AIP ADVANCES 10 巻 ( 4 ) 2020年4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：AIP Advances

Gamma-ray irradiations of up to 500 kGy on homoepitaxial n-type GaN layers were carried out, and the formation of electron traps was investigated by deep-level transient spectroscopy (DLTS) using Ni Schottky barrier diodes (SBDs). Before performing DLTS, current-voltage (I-V) and capacitance-voltage (C-V) measurements of the SBDs were performed and it was found that there was no change in the net donor concentration, ideality factor, and Schottky barrier height after irradiation. In the DLTS measurements, two new peaks, labeled G1 and G2, were observed after irradiation. The filling pulse width dependence of G1 revealed that the peak consists of two electron trap levels, labeled G1a (EC - 0.13 eV) and G1b (EC - 0.14 eV). Isothermal capacitance transient spectroscopy measurements of samples with different Schottky barrier heights showed that the G2 peak is a complex peak consisting of at least three electron traps, labeled G2a (EC - 0.80 eV), G2b (EC - 0.98 eV), and G2c (EC - 1.08 eV). The production rates (formation rates of traps by gamma-ray irradiation) for each trap were obtained. Finally, we investigated the annealing behavior of each trap and found that G1b and G2b decreased by the same amount with increasing annealing temperature, suggesting that the behavior originates from a recombination of vacancy-interstitial (Frenkel) pairs.

DOI： 10.1063/1.5144158

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

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

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

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 査読有り

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

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

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

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

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

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

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 査読有り

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 査読有り

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

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

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

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

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

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

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

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

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

The origin of carbon-related carrier compensation in p-type GaN layers grown by MOVPE

Narita, T; Tomita, K; Tokuda, Y; Kogiso, T; Horita, M; Kachi, T

JOURNAL OF APPLIED PHYSICS 124 巻 ( 21 ) 2018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：Journal of Applied Physics

The role of carbon impurities in p-type GaN layers grown by metalorganic vapor phase epitaxy (MOVPE) was investigated. The lightly Mg-doped (∼1017 cm-3) p-type GaN samples with different carbon concentration [C] were prepared by controlling growth temperature and pressure. Temperature-dependent Hall-effect analyses exhibited an increase in donor concentration with increasing [C]. The low-temperature mobility also decreased with increasing [C], as a result of mobility limitation due to ionized impurity scattering. These results show that carbon atoms in MOVPE-grown p-GaN layers act as ionized donors and cause carrier compensation. Deep-level transient spectroscopy (DLTS) using bias pulses detected the existence of Hd traps (EV +0.88 eV) arising from the 0/-1 charge state of carbon on nitrogen sites (CN). The concentrations of Hd traps closely corresponded to [C] values in p-type GaN layers. Employing low-frequency capacitance DLTS to avoid carrier freeze-out at low temperatures, we newly discovered the Ha trap (EV +0.29 eV) whose concentration was directly proportional to the [C] value. These findings suggest that the Ha trap originates from CN identical to the Hd trap. Based on prior theoretical calculations of energy levels, the Ha trap can reasonably be assigned to a +1/0 donor state of CN. These results strongly suggest that a CN having two different charged states can compensate an electron and a hole in n-type and p-type GaN layers, respectively.

DOI： 10.1063/1.5057373

Phonon-assisted optical absorption due to Franz-Keldysh effect in 4H-SiC p-n junction diode under high reverse bias voltage

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

APPLIED PHYSICS EXPRESS 11 巻 ( 9 ) 2018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 Express

Photocurrent in a 4H-SiC p-n junction diode under illumination with sub-bandgap light was investigated. Under a high reverse bias condition, the photocurrent significantly increased with an increase in the reverse bias voltage. We calculated the photocurrent taking into consideration the phonon-assisted optical absorption due to the Franz-Keldysh effect. The calculated photocurrent showed good agreement with the experimental results. The photocurrent also increased at elevated temperatures, which could be quantitatively explained by the redshift of the 4H-SiC absorption edge (the shrinkage of the bandgap) and the increase in the phonon occupation number with rising temperature.

DOI： 10.7567/APEX.11.091302

Accurate method for estimating hole trap concentration in n-type GaN via minority carrier transient spectroscopy

Kanegae, K; Horita, M; Kimoto, T; Suda, J

APPLIED PHYSICS EXPRESS 11 巻 ( 7 ) 2018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 Express

We propose an analysis method for the accurate estimation of the hole trap (H1, EV + 0.85 eV) concentration in n-type GaN via minority carrier transient spectroscopy (MCTS). The proposed method considers both the hole occupation during a filling (current injection) period and the quick carrier recombination via the hole traps near the depletion layer edge immediately after a reverse bias is applied. The reverse bias voltage dependence of the MCTS spectrum indicates that an accurate trap concentration, as well as the hole diffusion length and electron capture cross section of the hole trap, can be determined.

DOI： 10.7567/APEX.11.071002

Characterization of carrier concentration and mobility of GaN bulk substrates by Raman scattering and infrared reflectance spectroscopies

Kanegae, K; Kaneko, M; Kimoto, T; Horita, M; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS 57 巻 ( 7 ) 2018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：Japanese Journal of Applied Physics

n-Type GaN bulk substrates with carrier concentrations (n) of 1016-1020 cm%3 were characterized by Raman scattering (350-5000 cm-1) and infrared reflectance (400-5000 cm%1) spectroscopies. Experimental spectra were fitted with the curves calculated from the dielectric function and carrier concentration and mobility of the GaN bulk. The obtained values agree well with the values from Hall-effect measurements for n of 1016-1019 cm-3 in Raman scattering measurements and for n of 1018-1020 cm-3 in infrared reflectance measurements.

DOI： 10.7567/JJAP.57.070309

Franz-Keldysh effect in GaN p-n junction diode under high reverse bias voltage

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

APPLIED PHYSICS LETTERS 112 巻 ( 25 ) 2018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：Applied Physics Letters

Photocurrent induced by sub-bandgap light absorption due to the Franz-Keldysh effect was observed in GaN p-n junction diodes under a high reverse bias voltage. The photocurrent increased with the reverse bias voltage and the increase was found to be more significant as the wavelength approached the absorption edge of GaN. The photocurrent was calculated with consideration of light absorption induced by the Franz-Keldysh effect in the depletion layer. The calculated curves showed excellent agreement with the experimental curves. The photocurrent also increased with an increase in temperature and this could be quantitatively explained by the red-shift of the GaN absorption edge with the increase in temperature.

DOI： 10.1063/1.5031215

Sources of carrier compensation in metalorganic vapor phase epitaxy-grown homoepitaxial n-type GaN layers with various doping concentrations

Sawada, N; Narita, T; Kanechika, M; Uesugi, T; Kachi, T; Horita, M; Kimoto, T; Suda, J

APPLIED PHYSICS EXPRESS 11 巻 ( 4 ) 2018年4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

The source of carrier compensation in metalorganic vapor phase epitaxy (MOVPE)-grown n-type GaN was quantitatively investigated by Halleffect measurement, deep-level transient spectroscopy, and secondary ion mass spectrometry. These analysis techniques revealed that there were at least three different compensation sources. The carrier compensation for samples with donor concentrations below 5 1016 cm3 can be explained by residual carbon and electron trap E3 (EC % 0.6 eV). For samples with higher donor concentrations, we found a proportional relationship between donor concentration and compensating acceptor concentration, which resulted from a third source of compensation. This is possibly due to the self-compensation effect.

DOI： 10.7567/APEX.11.041001

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 査読有り

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

2018 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM) 2018年

Characterization of lightly-doped n- and p-type homoepitaxial GaN on free-standing substrates 招待有り査読有り

Horita M., Suda J.

IMFEDK 2017 - 2017 International Meeting for Future of Electron Devices, Kansai 頁： 86 - 87 2017年7月

記述言語：英語出版者・発行元：IMFEDK 2017 - 2017 International Meeting for Future of Electron Devices, Kansai

Hall-effect measurements for n-type and p-type GaN with low doping concentration are presented. The GaN layers were grown by metal-organic vapor phase epitaxy on hydride-vapor-phase-epitaxy-grown free-standing GaN substrates. For n-GaN, the origin of acceptor which compensating donor is not only C but also native defects for the Si doping concentration of 1016 cm-3 level. The electron mobility is mainly limited by ionized impurity scattering or polar optical phonon scattering in the temperature less or higher than 200 K, respectively. For p-GaN, lightly Mg doping of mid 1016 cm-3 was achieved, which shows the donor concentration of 3.2×1016 cm-3 and the mobility of 31 cm2/Vs at 300 K.

DOI： 10.1109/IMFEDK.2017.7998055

Solution-derived SiO2 gate insulator formed by CO2 laser annealing for polycrystalline silicon thin-film transistors 査読有り

Daisuke Hishitani, Masahiro Horita, Yasuaki Ishikawa, Hiroshi Ikenoue, Yukiharu Uraoka

Japanese Journal of Applied Physics 56 巻 ( 5 ) 2017年5月

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

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

Applied Physics Express 10 巻 ( 5 ) 2017年5月

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

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

Japanese Journal of Applied Physics 56 巻 ( 3 ) 2017年3月

Characterization of lightly-doped n- and p-type homoepitaxial GaN on free-standing substrates 招待有り査読有り

Horita, M; Suda, J

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

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) 頁： 86-87 2017年

　前のページ - 次のページ　

1