Faculty Profiles - HORITA Masahiro

Papers - HORITA Masahiro

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Depth Analyses of Acceptor and Compensating Donor Concentrations in Mg-Ion-Implanted GaN with Ultra-High-Pressure Annealing Open Access

Sumida, K; Kataoka, K; Narita, T; Horita, M; Kachi, T; Suda, J

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 2025.3

Publisher：Physica Status Solidi (B): Basic Research

Depth analyses of acceptor concentration (Na) and compensating donor concentration (Nd) are presented for Mg-ion-implanted GaN after ultra-high-pressure annealing (UHPA). The UHPA processes are carried out at 1300 °C under 500 MPa of nitrogen for various annealing durations. Photoluminescence measurements combined with stepwise etching reveal the depth dependence of Na in both the Mg-ion-implanted region and the diffusion region where Mg atoms diffuse deeply during UHPA. In the early stage of UHPA (5 min), Na in the implanted region is approximately one-tenth that of the Mg concentration ([Mg]), whereas Na in the diffusion region is close to [Mg], indicating that the Mg activation in the implanted region requires a longer UHPA duration than that in the diffusion region. Na and Nd in the implanted region are estimated from Hall-effect measurements and a step etching. Na after 15 min UHPA reaches sufficiently high level (Na ≈ [Mg]); however, Nd remains high (Nd/Na ≈ 50%) and diminishes with the prolongation of UHPA duration (60 min), reaching a low level (Nd/Na ≈ 20%). These findings indicate that the required UHPA duration is determined by the time needed to achieve a significant reduction in Nd within the implanted region.

DOI： 10.1002/pssb.202400613

Free electron mobility limited by fixed charges and trapped electrons in 4H-SiC (1120) and (1100) MOSFETs annealed in NO

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 64 ( 1 ) 2025.1

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The impact of Coulomb scattering by fixed charges and trapped electrons on the free electron mobility (μfree) of SiC(11 2 ¯ 0) and (1 1 ¯ 00) MOSFETs annealed in NO was quantitatively discussed through numerical calculations. The fixed charge density for MOSFETs on (11 2 ¯ 0) and (1 1 ¯ 00) annealed in NO was estimated to be 1.0 × 1013 cm−2, which is four times higher than that for (0001) MOSFETs previously reported. Calculation of μfree can well reproduce the experimental Hall mobilities for all MOSFETs on (11 2 ¯ 0) and (1 1 ¯ 00) within the wide range of effective normal field (0.08 MV cm−1 ≤ Eeff ≤ 0.78 MV cm−1).

DOI： 10.35848/1347-4065/ada1b7

Engineered interface charges and traps in GaN MOSFETs providing high channel mobility and <i>E</i>-mode operation Open Access

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 63 ( 12 ) 2024.12

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

This review focuses on controlling interface charges and traps to obtain minimal channel resistance and stable enhancement-mode operation in GaN MOSFETs. Interface traps reduce the free electron density and act as Coulomb scattering centers, thus reducing the channel mobility. Oxide traps cause instability of threshold voltage (Vth) by trapping electrons or holes under gate bias. In addition, the Vth is affected by the overall distribution of interface charges. The first key is a design of a bilayer structure to simultaneously obtain good insulating properties and interface properties. The other key is the optimization of post-deposition annealing to minimize oxide traps and interface fixed charges. Consequently, the gate structure of an AlSiO/AlN/p-type GaN has been designed. Reductions in Vth as a result of polarization charges can be eliminated using an m-plane trench channel, resulting in a channel mobility of 150 cm2 V-1s-1 and Vth of 1.3 V.

DOI： 10.35848/1347-4065/ad8c4f

Transport Properties in GaN Metal-Oxide-Semiconductor Field-Effect Transistor Almost Free of Interface Traps with AlSiO/AlN/p-Type GaN Gate Stack

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

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Vol. 18 ( 12 ) 2024.12

Publisher：Physica Status Solidi - Rapid Research Letters

The factors limiting channel mobility in AlSiO/p-type GaN metal–oxide–semiconductor (MOS) field-effect transistors are examined by performing Hall-effect measurements in conjunction with a gate bias, with and without a thin AlN interlayer. In the absence of this interlayer, the free carrier concentration associated with the Hall effect is significantly reduced compared with the net gate charge density estimated from capacitance–voltage data, indicating that electrons are trapped to a significant extent at the MOS interface. These interface traps are found to have an energy ≈20 meV above the Fermi level in strong inversion based on temperature-dependent Hall effect data. The insertion of a 0.8 nm-thick AlN interlayer eliminates charge trapping such that almost all gate charges are mobile. The mobility components could be divided into types based on their effect on the effective electric field perpendicular to the channel. Coulomb scattering centers resulting from interface states are evidently reduced by inserting the AlN interlayer, which also enhances the channel mobility to over 150 cm2 V−1s−1.

DOI： 10.1002/pssr.202400141

Impact of Coulomb scattering due to trapped electrons on Hall mobilities in 4H-SiC (11(2)over-bar0) and (1(1)over-bar00) MOSFETs annealed in NO

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 63 ( 11 ) 2024.11

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The temperature dependence of Hall mobility (μ Hall) of 4H-SiC(11 2 ¯ 0) and (1 1 ¯ 00) metal-oxide-semiconductor field-effect transistors (MOSFETs) with the gate oxides annealed in NO is compared with that of MOSFETs on (0001) annealed in NO or POCl3. Coulomb scattering due to trapped electrons, which is reported to be significant in MOSFETs on (0001) annealed in NO, may be the primary limiting factor of μ Hall for MOSFETs on (11 2 ¯ 0) and (1 1 ¯ 00) annealed in NO. Furthermore, the difference in μ Hall among the MOSFETs is highlighted at 77 K, which may be attributed to the suppression of phonon scattering and the presence of strong Coulomb scattering.

DOI： 10.35848/1347-4065/ad879d

A distinctive bound exciton line induced by electron-beam irradiation and subsequent annealing of an unintentionally doped GaN layer

Iguchi, H; Kataoka, K; Horita, M; Narita, T; Yamada, S; Tomita, K; Kachi, T; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 63 ( 11 ) 2024.11

Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

An undefined bound exciton line (UDX) with a photon energy 0.6 meV lower than the Si-donor bound exciton line was observed by photoluminescence in gallium nitride (GaN) layers annealed at 1100 °C after electron beam (EB) irradiation at an energy of 137-2000 keV. The UDX was not observed in samples not subjected to EB irradiation or annealing but was found in a sample annealed after EB irradiation at an energy of 137 keV, where only nitrogen atoms are displaced in GaN. The origin of the UDX was presumably formed by a thermal reaction of defects containing nitrogen-displacement-related defects.

DOI： 10.35848/1347-4065/ad918a

Influence of fixed charges and trapped electrons on free electron mobility at 4H-SiC(0001)/SiO<sub>2</sub> interfaces with gate oxides annealed in NO or POCl<sub>3</sub> Open Access

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

APPLIED PHYSICS EXPRESS Vol. 17 ( 8 ) 2024.8

Publisher：Applied Physics Express

Free electron mobility (μ free) in 4H-SiC(0001) MOSFETs with gate oxides annealed in NO or POCl3 was calculated in a wide range of effective normal field (E eff) from 0.02 to 2 MV cm−1, taking account of scattering by fixed charges and trapped electrons. The present calculation indicates that the Hall mobility in the high-E eff region experimentally obtained for NO-annealed MOSFETs (14 cm2 V−1 s−1 at 1.1 MV cm−1) is much lower than that for POCl3-annealed MOSFETs (41 cm2 V−1 s−1) due to severe Coulomb scattering by electrons trapped at a very high density of interface states.

DOI： 10.35848/1882-0786/ad63ef

Nitrogen-displacement-related recombination centers generated by electron beam irradiation in n-type and p-type homoepitaxial GaN layers Reviewed Open Access

Endo, M; Horita, M; Suda, J

APPLIED PHYSICS EXPRESS Vol. 17 ( 1 ) 2024.1

Language：English Publisher：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> Reviewed

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

APPLIED PHYSICS EXPRESS Vol. 16 ( 7 ) 2023.7

Language：English Publisher：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 Reviewed

Aoshima, K; Horita, M; Suda, J

APPLIED PHYSICS LETTERS Vol. 122 ( 1 ) 2023.1

Language：English Publisher：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 Reviewed

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

Language：English Publisher：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 Reviewed

Iguchi H., Horita M., Suda J.

Applied Physics Express Vol. 15 ( 12 ) 2022.12

Language：English Publisher：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 Reviewed Open Access

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 Vol. 132 ( 13 ) 2022.10

Language：English Publisher：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 Reviewed

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( 9 ) 2022.9

Language：English Publisher：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 Reviewed

Iguchi, H; Horita, M; Suda, J

APPLIED PHYSICS EXPRESS Vol. 15 ( 7 ) 2022.7

Language：English Publisher：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 Reviewed Open Access

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( SC ) 2022.5

Language：English Publisher：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 Reviewed

Endo, M; Horita, M; Suda, J

APPLIED PHYSICS LETTERS Vol. 120 ( 14 ) 2022.4

Language：English Publisher：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 Reviewed

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

IEEE ELECTRON DEVICE LETTERS Vol. 43 ( 1 ) page： 96 - 99 2022.1

Language：English Publisher：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 Reviewed

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

APPLIED PHYSICS EXPRESS Vol. 14 ( 12 ) 2021.12

Language：English Publisher：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 Reviewed Open Access

Aoshima, K; Horita, M; Suda, J

AIP ADVANCES Vol. 11 ( 11 ) 2021.11

Language：English Publisher：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

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