Faculty Profiles - SUDA Jun

Papers - SUDA Jun

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

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

APPLIED PHYSICS EXPRESS Vol. 16 ( 7 ) 2023.7

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

RF characteristics of 150-nm AlGaN/GaN high electron mobility transistors fabricated using <i>i</i>-line stepper lithography Open Access

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

ELECTRONICS LETTERS Vol. 59 ( 10 ) 2023.5

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

This article reports radio frequency characteristics of 150-nm gate aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high electron mobility transistors (HEMTs) fabricated using i-line stepper lithography and a thermal reflow technique. The authors have developed two different gate structures that were a field-plated gate using the lift-off process and a Y-shaped gate using the ion-milling process. Fabricated HEMTs using these different gate structures exhibited nearly equivalent DC characteristics. The field-plated gate device showed a unity current gain cutoff frequency (fT) of 35 GHz and a maximum oscillation frequency (fmax) of 106 GHz, while the Y-shaped gate device showed fT of 36 GHz and fmax of 115 GHz. The equivalent circuit analysis indicated a decrease in the gate-drain capacitance and the drain conductance is responsible for the improved fmax in the Y-shaped gate device.

DOI： 10.1049/ell2.12798

Effects of proton irradiation-induced point defects on Shockley-Read-Hall recombination lifetimes in homoepitaxial GaN p-n junctions

Narita, T; Kanechika, M; Tomita, K; Nagasato, Y; Kondo, T; Uesugi, T; Ikeda, S; Kosaki, M; Oka, T; Suda, J

APPLIED PHYSICS LETTERS Vol. 122 ( 11 ) 2023.3

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

This work examined the intentional generation of recombination centers in GaN p-n junctions on freestanding GaN substrates. Irradiation with a 4.2 MeV proton beam was used to create a uniform distribution of vacancies and interstitials across GaN p+/n- and p-/n+ junctions through anode electrodes. With increasing proton dose, the effective doping concentrations were found to be reduced. Because the reduction in the doping concentration was much higher than the hydrogen atom concentration, this decrease could not be attributed solely to carrier compensation resulting from interstitial hydrogen atoms. In fact, more than half of the electron and hole compensation was caused by the presence of point defects. These defects evidently served as Shockley-Read-Hall (SRH) recombination centers such that the SRH lifetimes were reduced to several picoseconds from several hundred picoseconds prior to irradiation. The compensation for holes in the p-/n+ junctions was almost double that for electrons in the p+/n- junctions. Furthermore, the SRH lifetimes associated with p-/n+ junctions were shorter than those for p+/n- junctions for a given proton dose. These differences can be explained by variations in the charge state and/or the formation energy of intrinsic point defects in the p-type and n-type GaN layers. The results of the present work indicate the asymmetry of defect formation in GaN based on the fact that intrinsic point defects in p-type GaN readily compensate for holes.

DOI： 10.1063/5.0141781

Comparative study of electrical properties of semi-insulating GaN substrates grown by hydride vapor phase epitaxy and doped with Fe, C, or Mn

Tanaka, D; Iso, K; Suda, J

JOURNAL OF APPLIED PHYSICS Vol. 133 ( 5 ) 2023.2

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

The electrical properties of semi-insulating GaN substrates doped with iron (Fe), carbon (C), or manganese (Mn) grown by hydride vapor phase epitaxy are presented. Hall effect measurements were performed at temperatures ranging from 300 to 800 K. At all of the investigated temperatures, the Mn-doped samples exhibited the highest resistivity. The Fe-doped samples showed n-type conduction, whereas the C-doped samples and the Mn-doped sample with a Mn concentration of 1 × 1019 cm-3 showed p-type conduction. A detailed analysis of the temperature dependence of the carrier concentration showed that all of the impurities formed acceptor levels at EC -(0.59-0.61) eV for Fe, at EV +(0.90-1.07) eV for C, and at EV +1.55 eV for Mn. The Mn-doped sample with a Mn concentration of 8 × 1017 cm-3 showed a negative Hall coefficient (suggesting n-type conduction) at high temperatures, contradicting the formation of acceptor levels by Mn. We successfully explained the negative value by considering the conduction of both holes and electrons with different mobilities. On the basis of the results, we calculated the relationship between the resistivity and doping concentration for each dopant. The calculations indicated that the highest resistivity can be realized in Mn-doped GaN with an optimized doping concentration (depending on the residual donor concentration). All of the dopants can effectively realize high resistivity at room temperature. Mn is an effective dopant for attaining high resistivity, especially at high temperatures (e.g., 800 K).

DOI： 10.1063/5.0131470

Effect of H<sub>2</sub> addition on growth rate and surface morphology of GaN(0001) grown by halide-vapor-phase epitaxy using GaCl<sub>3</sub>

Hara, K; Yamamoto, E; Ohara, J; Kojima, J; Onda, S; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( 2 ) 2023.2

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

We investigated the effect of H2 addition in halide-vapor-phase epitaxy of GaN on Ga-polar GaN(0001) using an external GaCl3 supply method. To overcome the problem of the very low growth rate on GaN(0001) using GaCl3, we intentionally added H2 to convert GaCl3 to GaCl in the reactor. Using this approach, we successfully increased the growth rate, and also improved the surface morphology of the grown layer.

DOI： 10.35848/1347-4065/acb97b

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

Aoshima, K; Horita, M; Suda, J

APPLIED PHYSICS LETTERS Vol. 122 ( 1 ) 2023.1

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

Comparison of switching performance of high-speed GaN vertical MOSFETs with various gate structures based on TCAD simulation

Ishida, T; Kachi, T; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( 1 ) 2023.1

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

To evaluate the impact of gate structures on the switching performance (R on Q g) and cost (required chip size, proportional to R on A) of GaN vertical MOSFETs, we calculated the R on AR on Q g of trench-gate structures with and without a countermeasure to reduce the electric field applied to the gate insulator, as well as a planar structure with various cell pitches, channel mobilities, and blocking voltages. When the blocking voltage was 600 V, the planar-gate structure achieved the lowest R on AR on Q g owing to its low Q g/A, despite the high R on A. However, when the blocking voltage was 1800 V, a trench-gate structure without the countermeasure achieved the lowest R on AR on Q g owing to its low R on A and optimal cell pitch. The R on AR on Q g of a trench-gate structure with a countermeasure and planar-gate structure became close with increasing channel mobility. This indicates that high channel mobility is the most important factor, rather than the selection of the device structure.

DOI： 10.35848/1347-4065/aca266

Demonstration of AlN-based Vertical p-n Diodes with Dopant-Free Distributed-Polarization Doping

Kumabe T., Yoshikawa A., Kushimoto M., Honda Y., Arai M., Suda J., Amano H.

Technical Digest - International Electron Devices Meeting, IEDM 2023

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

Nearly ideal AlN-based vertical p-n diodes are demonstrated on an AIN substrate utilizing dopant-free distributed-polarization doping (DPD). Capacitance-voltage measurements revealed that the effective doping concentration agreed well with the designed DPD charge concentration. The fabricated devices exhibited a low tum-on voltage of 6.5 V, a low differential specific ON-resistance of 3 mO cm2, 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, which was almost twice as high as the reported critical electric field of 4H-SÌC and GaN. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.

DOI： 10.1109/IEDM45741.2023.10413866

Annealing properties of vacancy-type defects in ion implanted GaN during ultra-high-pressure annealing studied by using a monoenergetic positron beam

Uedono, A; Sakurai, H; Uzuhashi, J; Narita, T; Sierakowski, K; Ishibashi, S; Chichibu, SF; Bockowski, M; Suda, J; Ohkubo, T; Ikarashi, N; Hono, K; Kachi, T

GALLIUM NITRIDE MATERIALS AND DEVICES XVIII Vol. 12421 2023

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

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 Publishing type：Research paper (scientific journal) 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

Reliability issues of gate oxides and <i>p</i>-<i>n</i> junctions for vertical GaN metal-oxide-semiconductor field-effect transistors (Invited)

Narita, T; Kikuta, D; Ito, K; Shoji, T; Mori, T; Yamaguchi, S; Kimoto, Y; Tomita, K; Kanechika, M; Kondo, T; Uesugi, T; Kojima, J; Suda, J; Nagasato, Y; Ikeda, S; Watanabe, H; Kosaki, M; Oka, T

2023 IEEE INTERNATIONAL RELIABILITY PHYSICS SYMPOSIUM, IRPS Vol. 2023-March 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE International Reliability Physics Symposium Proceedings

We focus on reliability issues of gate oxides and p-n junctions to realize vertical GaN metal-oxide-semiconductor field-effect transistors (MOSFETs). An annealed AlSiO gate oxide on GaN displayed a lifetime of over 20 years at 150 °C and suppressed positive bias instability in MOSFETs. The key to high channel mobility and stability under positive gate bias is the interface structure designed to minimize oxide border traps. We also evaluated the reliability of GaN p-n diodes (PNDs) on freestanding GaN substrates with different threading dislocation densities. The reverse leakage for PNDs involving threading dislocations was explained by variable-range hopping, while the reverse leakage for dislocation-free PNDs was dominated by band-to-band tunneling. The fabricated PNDs demonstrated excellent robustness under high-temperature reverse bias. However, after continuous forward current stress, reverse leakage pathways were formed at threading screw dislocations, which should be minimized in future GaN substrates.

DOI： 10.1109/IRPS48203.2023.10118047

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

Iguchi H., Horita M., Suda J.

Applied Physics Express Vol. 15 ( 12 ) 2022.12

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

Mg-implanted vertical GaN junction barrier Schottky rectifiers with low on resistance, low turn-on voltage, and nearly ideal nondestructive breakdown voltage Open Access

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

APPLIED PHYSICS LETTERS Vol. 121 ( 20 ) 2022.11

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

Vertical GaN junction barrier Schottky (JBS) diodes with superior electrical characteristics and nondestructive breakdown were realized using selective-Area p-Type doping via Mg ion implantation and subsequent ultra-high-pressure annealing. Mg-ion implantation was performed into a 10 μm thick Si-doped GaN drift layer grown on a free-standing n-Type GaN substrate. We fabricated the JBS diodes with different n-Type GaN channel widths Ln = 1 and 1.5 μm. The JBS diodes, depending on Ln, exhibited on-resistance (RON) between 0.57 and 0.67 mω cm2, which is a record low value for vertical GaN Schottky barrier diodes (SBDs) and high breakdown (BV) between 660 and 675 V (84.4% of the ideal parallel plane BV). The obtained low RON of JBS diodes can be well explained in terms of the RON model, which includes n-Type GaN channel resistance, spreading current effect, and substrate resistance. The reverse leakage current in JBS diodes was relatively low 103-104 times lower than in GaN SBDs. In addition, the JBS diode with lower Ln exhibited the leakage current significantly smaller (up to reverse bias 300 V) than in the JBS diode with large Ln, which was explained in terms of the reduced electric field near the Schottky interface. Furthermore, the JBS diodes showed a very high current density of 5.5 kA/cm2, a low turn-on voltage of 0.74 V, and no destruction against the rapid increase in the reverse current approximately by two orders of magnitude. This work demonstrated that GaN JBS diodes can be strong candidates for low loss power switching applications.

DOI： 10.1063/5.0106321

Process engineering of GaN power devices via selective-area p-type doping with ion implantation and ultra-high-pressure annealing 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 Publishing type：Research paper (scientific journal) 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

Effect of Ultra-High-Pressure Annealing on Defect Reactions in Ion-Implanted GaN Studied by Positron Annihilation

Uedono, A; Sakurai, H; Uzuhashi, J; Narita, T; Sierakowski, K; Ishibashi, S; Chichibu, SF; Bockowski, M; Suda, J; Ohkubo, T; Ikarashi, N; Hono, K; Kachi, T

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 259 ( 10 ) 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (B) Basic Research

Herein, the annealing behaviors of defects in ion-implanted GaN are studied by positron annihilation, cathodoluminescence, scanning transmission electron microscopy, and atom probe tomography. Si or Mg ions are implanted into GaN to obtain 300 nm deep box profiles of the impurities. The samples are annealed up to 1480 °C under a N2 pressure of 1 GPa. For as-implanted GaN, the major defect species is identified as Ga-vacancy-type defects. After annealing above 1000 °C, vacancy clusters are introduced, and they remain even after 1480 °C annealing. For Mg-implanted GaN with the Mg concentration ([Mg]) ≤ 1018 cm−3, no large change in the depth distribution of Mg is observed before and after annealing at 1400 °C. For the sample with [Mg] = 1019 cm−3, however, Mg diffuses into the bulk, which is attributed to the over-doping of Mg and their vacancy-assisted diffusion. The Mg diffusion is suppressed, and the donor–acceptor pair emission is enhanced by sequential N-implantation, which is attributed to the reaction between Mg and vacancies under a N-rich condition. For the samples annealed at 1480 °C, an accumulation of Mg around dislocation loops and Mg clustering are enhanced by the N-implantation.

DOI： 10.1002/pssb.202200183

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

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

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

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

Atomic resolution analysis of extended defects and Mg agglomeration in Mg-ion-implanted GaN and their impacts on acceptor formation

Kano, E; Kataoka, K; Uzuhashi, J; Chokawa, K; Sakurai, H; Uedono, A; Narita, T; Sierakowski, K; Bockowski, M; Otsuki, R; Kobayashi, K; Itoh, Y; Nagao, M; Ohkubo, T; Hono, K; Suda, J; Kachi, T; Ikarashi, N

JOURNAL OF APPLIED PHYSICS Vol. 132 ( 6 ) 2022.8

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

We carried out atomic-scale observations of Mg-ion-implanted GaN by transmission electron microscopy (TEM) and atom probe tomography (APT) to clarify the crystallographic structures of extended defects and Mg agglomerations that form during post-implantation annealing. The complementary TEM and APT analyses have shown that Mg atoms agglomerate at dislocations that bound extended defects. The concentration of Mg is higher at the dislocations with a larger Burgers vector. This indicates that Mg agglomeration is caused by the pressure at the dislocations. Mg concentration in highly Mg-rich regions is 1 at. %, which exceeds the solubility limit of Mg in GaN. We investigated isothermal and isochronal evolution of the defects by TEM, cathodoluminescence analysis, and positron annihilation spectroscopy. The results indicated that the intensity of donor-acceptor pair emission increases with the annealing temperature and duration and reaches a maximum after elimination of the extended defects with highly Mg-rich regions. These results strongly suggest that such extended defects reduce the acceptor formation and that they as well as the previously reported compensating centers, such as N-related vacancies, can inhibit the formation of p-type GaN. The mechanism by which the extended defects reduce acceptor formation is discussed.

DOI： 10.1063/5.0097866

Suppression of cluster formation in GaN growth by tri-halide vapor phase epitaxy with external GaCl<sub>3</sub> gas supply system

Hara, K; Yamamoto, E; Kozawa, M; Uematsu, D; Ohara, J; Mukaiyama, Y; Kojima, J; Onda, S; Suda, J

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 61 ( 7 ) 2022.7

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

One critical issue hindering high-quality, high-speed growth of GaN is cluster formation in the gas phase. We investigated cluster formation in tri-halide vapor phase epitaxial growth of GaN. The growth system is equipped with an external GaCl3 gas supply system. We observed cluster formation under certain growth conditions experimentally. A simulation was also carried out to reveal the critical conditions for cluster formation. We propose that increasing the gas temperature is an effective way to suppress cluster formation, and thus achieve a higher growth rate with a flat surface morphology.

DOI： 10.35848/1347-4065/ac7a7a

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

Iguchi, H; Horita, M; Suda, J

APPLIED PHYSICS EXPRESS Vol. 15 ( 7 ) 2022.7

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

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

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

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

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