研究者詳細 - 堀田　昌宏

論文 - 堀田　昌宏

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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 Open Access

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 Open Access

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 Open Access

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

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