Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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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

Language：English Publishing type：Research paper (scientific journal) 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

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

Language：English Publishing type：Research paper (scientific journal) 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

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

Language：English Publishing type：Research paper (scientific journal) 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

Improvement of Gate Length Dependence in Electrical Characteristics of AlGaN/GaN Dual-Gate HEMTs

Ando, Y; Takahashi, H; Makisako, R; Wakejima, A; Suda, J

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 9 ) page： 5280 - 5288 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

This article examines the impact of gate length (Lg) on the dc, pulsed I-V, and small-signal characteristics of dual-gate (DG) AlGaN/GaN high electron mobility transistors (HEMTs). T-shaped DG structures with gate lengths ranging from 0.1 to 0.3μ m were fabricated using i-line stepper lithography and a thermal reflow technique. The short-channel effect was successfully eliminated in the DG devices, while single-gate (SG) devices fabricated on the same wafer were significantly affected by this phenomenon. The dependence of current collapse on Lg in the DG devices showed a reduction in the collapse by a factor of 5 or more compared to the SG devices. Furthermore, a 120-nm DG-HEMT exhibited a 10-dB reduction in the isolation and an extrapolated maximum oscillation frequency of 239 GHz, whereas a 110-nm SG-HEMT exhibited that of 146 GHz.

DOI： 10.1109/TED.2024.3430889

Study on the Impact of Mg-Channeled Implantation on Junction Termination Extension for GaN Vertical Power Devices Using TCAD Simulation

Kitagawa, K; Matys, M; Kachi, T; Suda, J

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 9 ) page： 5239 - 5244 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

This study investigates the influence of different magnesium (Mg) ion implantation techniques on the performance of gallium nitride (GaN)-based junction termination extension (JTE) structures. To this end, we perform a systematic TCAD simulation study on JTE structures using two different implantation techniques of Mg ions: 1) channeled implantation and 2) random (conventional) implantation. We perform channeled and random Mg ion implantations and subsequent activation annealing to GaN epitaxial layers to obtain actual Mg depth profiles experimentally. We used the obtained profiles for the TCAD simulations. The Mg-channeled implanted JTE structure exhibits a significantly larger optimal JTE dose window compared to the Mg-random implanted JTE structure. This is because, in the JTE structure with a channeled Mg depth profile, the electric field crowding is more suppressed than in the JTE structure with a random Mg depth profile. These results indicate that deep-graded Mg depth profiles are more suitable for the relaxation of electric field strength concentrations than shallower profiles. In addition, we found that the Mg-channeling-based JTE structure was more advantageous than the Mg-random-based JTE structure that considers the interface charge at the passivation SiO2/GaN interface.

DOI： 10.1109/TED.2024.3427103

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

Language：English Publishing type：Research paper (scientific journal) 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

Impacts of vacancy complexes on the room-temperature photoluminescence lifetimes of state-of-the-art GaN substrates, epitaxial layers, and Mg-implanted layers Open Access

Chichibu, SF; Shima, K; Uedono, A; Ishibashi, S; Iguchi, H; Narita, T; Kataoka, K; Tanaka, R; Takashima, S; Ueno, K; Edo, M; Watanabe, H; Tanaka, A; Honda, Y; Suda, J; Amano, H; Kachi, T; Nabatame, T; Irokawa, Y; Koide, Y

JOURNAL OF APPLIED PHYSICS Vol. 135 ( 18 ) 2024.5

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

For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely, nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified, and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission ( τ PL RT ) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, τ PL RT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm−3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively, while major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3-4, in ammonothermal GaN. The values of τ PL RT in n-GaN samples are compared with those of p-GaN, in which τ PL RT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers and by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealing, respectively.

DOI： 10.1063/5.0201931

Demonstration of AlGaN-on-AlN p-n Diodes With Dopant-Free Distributed Polarization Doping Open Access

Kumabe, T; Yoshikawa, A; Kawasaki, S; Kushimoto, M; Honda, Y; Arai, M; Suda, J; Amano, H

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 5 ) page： 3396 - 3402 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

Nearly ideal vertical AlxGa-{{1}-{x}}text{N} ({0.7} leq {x} < {1.0} ) p-n diodes are fabricated on an aluminum nitride (AlN) substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity doping, to overcome the major bottleneck of AlN-based material: the control of conductivity. Capacitance-voltage measurements revealed that the net charge concentration agreed well with the DPD charge concentration expected from the device layer structure. The fabricated devices exhibited a low turn-on voltage of 6.5 V, a low differential specific on-resistance of 3 text{M}Omega cm2, electroluminescence (maximum at 5.1 eV), and an ideality factor of 2 for a wide range of temperatures (room temperature - 573 K). Moreover, the breakdown electric field was 7.3 MV cm-1, which was almost twice as high as the reported critical electric field of GaN at the same doping concentration. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

DOI： 10.1109/TED.2024.3367314

Electrical Characterization of AlGaN/ GaN-HEMTs on Semi-Insulating GaN Substrates Doped With Fe, C, or Mn and Grown by Hydride Vapor Phase Epitaxy

Tanaka, D; Iso, K; Makisako, R; Ando, Y; Suda, J

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 5 ) page： 3096 - 3101 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

This article reports a comparative study on the effect of dopants in semi-insulating GaN substrates grown by hydride vapor phase epitaxy (HVPE) on the electrical characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs). GaN-HEMTs were fabricated on GaN substrates doped with iron (Fe), carbon (C), or manganese (Mn), and their electrical characteristics from 300 to 600 K were compared. Similar on-state characteristics were observed at room temperature, regardless of the substrate dopant. However, in the off-state breakdown characteristics, the devices on the C- and Mn-doped substrates showed slightly lower gate leakage currents than those on the Fe-doped substrate. Pulsed {I} -{V} characteristics showed that all devices had a small current collapse of approximately 10% or less, although the devices on the C- and Mn-doped substrates had slightly larger current collapse than that on the Fe-doped substrate. Furthermore, the temperature dependence of the off-state breakdown characteristics showed that the devices on the C- and Mn-doped substrates had a breakdown voltage ({V}-{text {BD}} ) that exceeded 100 V, even at 600 K, while that for the device on the Fe-doped substrate was less than 20 V. Arrhenius plots of leakage current suggested that for the devices on the Fe-doped substrate, current conduction through the substrate occurred above 350 K, which resulted in a low {V}-{text {BD}}. The devices on the C- and Mn-doped substrates had low leakage through the substrate due to the high resistivity of the substrate. These results indicate the feasibility of C- or Mn-doped GaN as HEMT substrates for use in high-voltage and high-temperature applications.

DOI： 10.1109/TED.2024.3375837

Improved Turn-On Voltage Controllability in AlGaN/GaN Gated-Anode Diodes Using Etch Endpoint Detection Layer Open Access

Ando, Y; Oishi, K; Takahashi, H; Makisako, R; Wakejima, A; Suda, J

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 71 ( 5 ) page： 2936 - 2942 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Electron Devices

AlGaN/GaN gated-anode diodes (GADs) have been proposed as microwave rectifying devices for microwave wireless power transmission (WPT) systems. However, achieving the desired turn-on voltage (Von) has posed a critical challenge due to the requirement for precise etching control. This article introduces a novel GAD structure aimed at enhancing productivity. In this new configuration, a GaN etch endpoint detection layer (GaN marker layer) is incorporated into the AlGaN layer, positioned approximately 4.5 nm away from the channel interface. During gate recess etching, the residual thickness of AlGaN is monitored using an optical interferometer. Etching is halted successfully upon detection of the GaN marker layer, signaled by an abrupt change in interference. Fabricated GADs consistently achieved the target Von of +0.20 V, exhibiting improved uniformity compared to prior GADs lacking a GaN marker layer. These devices typically demonstrated a maximum forward current of 0.69 A/mm and a reverse breakdown voltage exceeding 100 V. Additionally, a bridge-type rectifier circuit employing four GADs was simulated using a SPICE model constructed from measured pulse I-V characteristics and S-parameters. A conversion efficiency of 84% was predicted with an input power of 25.6 W (8 W/mm) at 5.8 GHz.

DOI： 10.1109/TED.2024.3381570

Realization of low specific-contact-resistance on N-polar GaN surfaces using heavily-Ge-doped n-type GaN films deposited by low-temperature reactive sputtering technique Open Access

Yamada, S; Shirai, M; Kobayashi, H; Arai, M; Kachi, T; Suda, J

APPLIED PHYSICS EXPRESS Vol. 17 ( 3 ) 2024.3

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

We developed a low-temperature ohmic contact formation process for N-polar GaN surfaces. Specific-contact-resistances of 9.4 × 10−5 and 2.0 × 10−5Ω cm2 were obtained using Ti/Al metal stacks on heavily-germanium-doped GaN films, which were deposited at 500 °C and 600 °C using a radical-assisted reactive sputtering method, respectively. The electrode sintering temperature was as low as 475 °C. Carrier concentrations for the 500 °C and 600 °C samples were 2.6 × 1020 and 1.8 × 1020cm−3, respectively. These results suggest that this method is highly effective in reducing the contact resistance of GaN devices with low thermal budgets.

DOI： 10.35848/1882-0786/ad2783

Suppression of threshold voltage shift due to positive bias stress in GaN planar MOSFETs by post-deposition annealing Open Access

Ichikawa, Y; Ueno, K; Kondo, T; Tanaka, R; Takashima, S; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 63 ( 2 ) 2024.2

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

Threshold voltage instability (shift) due to positive bias stress in GaN planar-gate MOSFETs was investigated. Gate dielectric (SiO2) was formed by remote-plasma-assisted CVD on homoepitaxial Mg-doped p-type GaN layers with Si-implanted n-type source and drain regions. The threshold voltage shift of 5.8 V was observed after a stress voltage of 30 V for a sample without post-deposition annealing (PDA). The threshold voltage shift was significantly reduced to 1.4 V for a sample with PDA (800 °C for 30 min). Stress time dependences up to 6000 s were measured, revealing that the main origin of the threshold voltage shift is electron trapping into near interface traps (NITs). These results suggest that PDA is effective for the reduction of the NITs.

DOI： 10.35848/1347-4065/ad0c43

Demonstration of recycling process for GaN substrates using laser slicing technique towards cost reduction of GaN vertical power MOSFETs Open Access

Ishida, T; Ushijima, T; Nakabayashi, S; Kato, K; Koyama, T; Nagasato, Y; Ohara, J; Hoshi, S; Nagaya, M; Hara, K; Kanemura, T; Taki, M; Yui, T; Hara, K; Kawaguchi, D; Kuno, K; Osajima, T; Kojima, J; Uesugi, T; Tanaka, A; Sasaoka, C; Onda, S; Suda, J

APPLIED PHYSICS EXPRESS Vol. 17 ( 2 ) 2024.2

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

To address the issue of the high cost of GaN substrates, a recycling process for GaN substrates using a laser slicing technique was investigated. The channel properties of lateral MOSFETs and the reverse characteristics of vertical PN diodes, which represent the main components of vertical power devices, exhibited no degradation either before and after laser slicing or due to the overall GaN substrate recycling process. This result indicates that the proposed recycling process is an effective method for reducing the cost of GaN substrates and has the potential to encourage the popularization of GaN vertical power devices.

DOI： 10.35848/1882-0786/ad269d

Improvement of AlSiO/GaN interface by a novel post deposition annealing using ultra high pressure Open Access

Kanechika, M; Hirata, T; Tokozumi, T; Kachi, T; Suda, J

APPLIED PHYSICS EXPRESS Vol. 17 ( 1 ) 2024.1

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

In this study, a novel post-deposition annealing (PDA) technique employing ultra-high pressure was demonstrated for the first time. A 40 nm thick AlSiO gate insulator was deposited using atomic layer deposition (ALD) on n-type gallium nitride (GaN) epitaxial layers grown on free-standing GaN substrates. These PDA techniques were performed at 600 °C in a nitrogen ambient under 400 MPa, with normal pressure conditions used as the references. The annealing duration varied within the range of 10, 30, 60, and 120 min. For normal pressure annealing, the flat-band voltage of capacitance-voltage curves exhibited a shift towards the positive bias direction as the annealing time increased. Conversely, for the 400 MPa annealing, the flat-band voltage approached the ideal curve as the annealing time extended. For 400 MPa and 120 min, low interface state density of ∼5 × 1011 cm−2 eV−1 or less at E c −0.20 eV was obtained. These results suggest that post-deposition annealing under ultra-high pressure could be a viable method for improving the interfacial characteristics of AlSiO/GaN.

DOI： 10.35848/1882-0786/ad0ba5

Record high electron mobilities in high-purity GaN by eliminating C-induced mobility collapse

Kaneki, S; Konno, T; Kimura, T; Kanegae, K; Suda, J; Fujikura, H

APPLIED PHYSICS LETTERS Vol. 124 ( 1 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Impact of carbon impurities on the electrical properties of lightly doped n-type GaN [electron concentration ∼( 1 - 2 ) × 10 15 cm − 3 at room temperature] was investigated using temperature-dependent Hall effect measurements. GaN crystals with a threading dislocation density of ( 1 - 3 ) × 10 6 c m − 2 were grown by our originally developed quartz-free hydride vapor phase epitaxy method, which enabled the background Si, O, and C concentrations to be suppressed to below the mid-1014 cm−3 range. We prepared three samples with different C concentrations ([C]) by intentional C doping. The C incorporation induced severe mobility collapse at temperatures greater than 60 K, where the measured mobility decreased and deviated from the theoretical value as [C] increased. The mobility collapse was eliminated for the purest GaN crystal with [C] ∼ 1.4 × 10 14 cm − 3 , exhibiting a record high room-temperature mobility of 1480 cm2/(V·s), as well as a record high maximum mobility of 14 300 cm2/(V·s) at 62 K. The latter was almost double the previous record. We found that the overall mobility behavior can be well reproduced by adding an empirical [C]-dependent mobility component expressed as μ UNK = K / T n UNK with 1 ≤ n UNK ≤ 2 and K ∝ C − 1 to the conventional mobility theory (phonon and impurity scattering). Although the mechanism of the component remains uncertain, our findings provide insight into the unsolved issue of mobility collapse.

DOI： 10.1063/5.0178086

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

Endo, M; Horita, M; Suda, J

APPLIED PHYSICS EXPRESS Vol. 17 ( 1 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) 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 channel mobility and stable E-mode operation in AlSiO/AlN/m-plane p-type GaN MOSFETs with little temperature dependence of the threshold voltage

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

Technical Digest - International Electron Devices Meeting, IEDM 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Technical Digest - International Electron Devices Meeting, IEDM

The polarization in a III-nitride system enhances conductivity in a MOS channel, while reduces the threshold voltage (Vth) and causes its temperature dependence. To simultaneously obtain a high channel mobility and a stable Emode operation, the gate insulator composed of an amorphous AlSiO and a crystalline AlN are applied to the mplane GaN channel using a trench gate structure. By inserting a 1.1 nm thick AlN, interface traps on a m-plane MOS channel are minimized, resulting in the effective mobility over 180 cm2 V–1s–1. Different from a MOSFET on a c-plane, the Vth value does not depend on the AlN thickness and is approximately 1 V for the acceptor doping at 1017 cm–3. Furthermore, the Vth on the m-plane GaN channel exhibits little temperature dependence in the range of 223 to 473 K because of no pyroelectric effect.

DOI： 10.1109/IEDM50854.2024.10873525

Design and fabrication of vertical GaN junction barrier Schottky rectifiers using Mg ion implantation Open Access

Matys, M; Kitagawa, K; Narita, T; Uesugi, T; Bockowski, M; Suda, J; Kachi, T

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( SN ) 2023.11

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

In this review, we briefly summarize the major challenges and our recent progress in the development of GaN Junction Barrier Schottky (JBS) diodes using selective-area p-type doping with ion implantation and ultra high-pressure annealing (UHPA) process. As a starting point, we discuss the properties of Schottky contacts in the context of UHPA and provide design principle for a high performance JBS diode. Next, we propose a JBS diode having p-type regions formed by channeled ion implantation. This kind of device can provide ultra-low leakage currents and a much better trade-off between on-resistance (R ON) and breakdown voltage (BV). Finally, we demonstrate our high-performance JBS diodes which exhibited the superior electrical characteristics (record low R ON from 0.57 to 0.67 mΩ cm2 and high BV from 660 to 675 V) and nondestructive breakdown.

DOI： 10.35848/1347-4065/acec69

Prospects of mist CVD for fabrication of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> MESFETs on <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> (010) substrates Open Access

Takane, H; Ando, Y; Takahashi, H; Makisako, R; Ikeda, H; Ueda, T; Suda, J; Tanaka, K; Fujita, S; Sugaya, H

APPLIED PHYSICS EXPRESS Vol. 16 ( 8 ) 2023.8

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

Mist CVD was applied to grow the β-Ga2O3 channel layer of a MESFET on a semi-insulating β-Ga2O3 (010) substrate. The mobility and carrier concentration of the channel layer were 80 cm2 V-1 s-1 and 6.2 × 1017 cm−3, respectively. The device exhibited a pinch-off characteristic with a threshold gate voltage of −9 V, and the maximum drain current was 240 mA mm−1. The maximum transconductance was 46 mS mm−1 and the on-resistance was 30 Ω mm. This device performance suggests that mist CVD is a potential growth technology capable of providing low-cost devices in the future.

DOI： 10.35848/1882-0786/acefa5

Electrical Characteristics of Gated Anode Diodes Based on Normally Off Recessed-Gate GaN High-Electron-Mobility Transistors for Rectenna Applications Open Access

Takahashi, H; Ando, Y; Tsuchiya, Y; Wakejima, A; Suda, J

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 220 ( 16 ) 2023.8

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

AlGaN/GaN high-electron-mobility transistor (HEMT)-based gated-anode diodes (GADs) for a 5.8 GHz rectenna application are proposed. An anode of the GAD is formed by connecting a gate and a drain of a normally off GaN HEMT. Herein, a wide recessed HEMT structure reported in the previous article is modified to a buried-type recessed gate HEMT structure. The gate-to-cathode distance is optimized to maximize device performance. Typical direct current (DC) characteristics of the HEMTs are a threshold voltage (Vth) of +0.4 V and a maximum drain current (Imax) of 450 mA mm−1. GADs using the HEMTs show the characteristics of maximum forward current (If) of 600 mA mm−1 and reverse breakdown voltage (BVr) of more than 100 V. The GAD using the recessed gate structure HEMT is shown to significantly improve If and BVr simultaneously compared to the previous work using the wide recessed gate structure. The rectifying performance of a bridge-type rectifier simulated with SPICE model of the GAD shows radio frequency (RF)–DC conversion efficiency of 84% and RF input power of 13 W at 5.8 GHz using four GADs with each gate width (Wg) of 400 μm.

DOI： 10.1002/pssa.202200837

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