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86 results on '"Yang, Gwangseok"'

2. Diffusion length of non-equilibrium minority charge carriers in β-Ga2O3 measured by electron beam induced current.

Author

Yakimov, E. B., Polyakov, A. Y., Smirnov, N. B., Shchemerov, I. V., Yang, Jiancheng, Ren, F., Yang, Gwangseok, Kim, Jihyun, and Pearton, S. J.

Subjects
GALLIUM compounds, ELECTRON beam induced current, SPATIAL distribution (Quantum optics), SCANNING electron microscopes, CHARGE carriers
Abstract

The spatial distribution of electron-hole pair generation in β-Ga2O3 as a function of scanning electron microscope (SEM) beam energy has been calculated by a Monte Carlo method. This spatial distribution is then used to obtain the diffusion length of charge carriers in high-quality epitaxial Ga2O3 films from the dependence of the electron beam induced current (EBIC) collection efficiency on the accelerating voltage of a SEM. The experimental results show, contrary to earlier theory, that holes are mobile in β-Ga2O3 and to a large extent determine the diffusion length of charge carriers. Diffusion lengths in the range 350–400 nm are determined for the as-grown Ga2O3, while processes like exposing the samples to proton irradiation essentially halve this value, showing the role of point defects in controlling minority carrier transport. The pitfalls related to using other popular EBIC-based methods assuming a point-like excitation function are demonstrated. Since the point defect type and the concentration in currently available Ga2O3 are dependent on the growth method and the doping concentration, accurate methods of diffusion length determination are critical to obtain quantitative comparisons of material quality. [ABSTRACT FROM AUTHOR]

Published
2018
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10. 10 MeV proton damage in β-Ga2O3 Schottky rectifiers

Author

Yang, Jiancheng, primary, Chen, Zhiting, additional, Ren, Fan, additional, Pearton, S. J., additional, Yang, Gwangseok, additional, Kim, Jihyun, additional, Lee, Jonathan, additional, Flitsiyan, Elena, additional, Chernyak, Leonid, additional, and Kuramata, Akito, additional

Published
2018
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22. Effect of proton irradiation energy on SiNx/AlGaN/GaN metal-insulator semiconductor high electron mobility transistors.

Author

Fares, Chaker, Ren, Fan, Pearton, Stephen J., Yang, Gwangseok, Kim, Jihyun, Lo, Chien-Fong, and Johnson, J. Wayne

Subjects
SILICON nitride, METAL-insulator-semiconductor devices, MODULATION-doped field-effect transistors, ELECTRON mobility, DIELECTRICS
Abstract

The effects of proton irradiation energy on the electrical properties of SiNx/AlGaN/GaN metal-insulator semiconductor high electron mobility transistors (MISHEMTs) using in situ grown silicon nitride as the gate dielectric were studied. The SiNx/AlGaN/GaN MISHEMT devices were irradiated with protons at energies of 5, 10, or 15 MeV at a fixed fluence of 2.5 × 1014 cm−2. The largest amount of device degradation was shown in the samples irradiated with the lowest irradiation energy of 5 MeV. The DC saturation current was reduced by 10.4%, 3.2%, and 0.5% for MISHEMTs irradiated with proton energies of 5, 10, and 15 MeV, respectively. Device performance degradation was more pronounced in the irradiated samples under high-frequency operation. At a frequency of 100 kHz, the percent saturation drain current reduction at a gate voltage of 3 V was 40%, 19%, and 17% after proton irradiation at 5, 10, and 15 MeV, respectively. The carrier removal rates for the MISHEMT devices were in the range of 21–144 cm−1 for the proton irradiation energies studied. The measured DC degradation and carrier removal rates are lower than the values reported for AlGaN/GaN metal-gate high electron mobility transistor devices irradiated at similar conditions, which can be attributed to the SiNx insulating layer reducing the total damage on the AlGaN surface. [ABSTRACT FROM AUTHOR]

Published
2018
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26. Effect of proton irradiation energy on AlGaN/GaN metal-oxide semiconductor high electron mobility transistors

Author

Ahn, Shihyun, primary, Dong, Chen, additional, Zhu, Weidi, additional, Kim, Byung-Jae, additional, Hwang, Ya-Hsi, additional, Ren, Fan, additional, Pearton, Stephen J., additional, Yang, Gwangseok, additional, Kim, Jihyun, additional, Patrick, Erin, additional, Tracy, Brian, additional, Smith, David J., additional, and Kravchenko, Ivan I., additional

Published
2015
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31. Point defect induced degradation of electrical properties of Ga2O3 by 10 MeV proton damage.

Author

Polyakov, A. Y., Smirnov, N. B., Shchemerov, I. V., Yakimov, E. B., Yang, Jiancheng, Ren, F., Yang, Gwangseok, Kim, Jihyun, Kuramata, A., and Pearton, S. J.

Subjects
EPITAXY, DEEP level transient spectroscopy, PROTONS, ELECTRONS, IRRADIATION
Abstract

Deep electron and hole traps in 10 MeV proton irradiated high-quality β-Ga2O3 films grown by Hydride Vapor Phase Epitaxy (HVPE) on bulk β-Ga2O3 substrates were measured by deep level transient spectroscopy with electrical and optical injection, capacitance-voltage profiling in the dark and under monochromatic irradiation, and also electron beam induced current. Proton irradiation caused the diffusion length of charge carriers to decrease from 350–380 µm in unirradiated samples to 190 µm for a fluence of 1014 cm-2, and this was correlated with an increase in density of hole traps with optical ionization threshold energy near 2.3 eV. These defects most likely determine the recombination lifetime in HVPE β-Ga2O3 epilayers. Electron traps at Ec-0.75 eV and Ec-1.2 eV present in as-grown samples increase in the concentration after irradiation and suggest that these centers involve native point defects. [ABSTRACT FROM AUTHOR]

Published
2018
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32. 10 MeV proton damage in b-Ga2O3 Schottky rectifiers.

Author

Yang, Jiancheng, Chen, Zhiting, Ren, Fan, Pearton, S. J., Yang, Gwangseok, Kim, Jihyun, Lee, Jonathan, Flitsiyan, Elena, Chernyak, Leonid, and Kuramata, Akito

Subjects
GALLIUM compounds, PROTON beams, SCHOTTKY effect, GALLIUM nitride films, POINT defects
Abstract

The electrical performance of vertical geometry Ga2O3 rectifiers was measured before and after 10MeV proton irradiation at a fixed fluence of 1014cm-2, as well as subsequent annealing up to 450 °C. Point defects introduced by the proton damage create trap states that reduce the carrier concentration in the Ga2O3, with a carrier removal rate of 235.7cm-1 for protons of this energy. The carrier removal rates under these conditions are comparable to GaN-based films and heterostructures. Even annealing at 300 °C produces a recovery of approximately half of the carriers in the Ga2O3, while annealing at 450 °C almost restores the reverse breakdown voltage. The on/off ratio of the rectifiers was severely degraded by proton damage and this was only partially recovered by 450 °C annealing. The minority carrier diffusion length decreased from ~340 nm in the starting material to ~315 nm after the proton irradiation. The reverse recovery characteristics showed little change with values in the range 20-30 ns before and after proton irradiation. [ABSTRACT FROM AUTHOR]

Published
2018
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39. Effect of 5 MeV proton radiation on DC performance and reliability of circular-shaped AlGaN/GaN high electron mobility transistors

Author

Xi, Yuyin, primary, Hsieh, Yueh-Ling, additional, Hwang, Ya-Hsi, additional, Li, Shun, additional, Ren, Fan, additional, Pearton, Stephen J., additional, Patrick, Erin, additional, Law, Mark E., additional, Yang, Gwangseok, additional, Kim, Hong-Yeol, additional, Kim, Jihyun, additional, Baca, Albert G., additional, Allerman, Andrew A., additional, and Sanchez, Carlos A., additional

Published
2014
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45. Influence of High-Energy Proton Irradiation on β-Ga2O3Nanobelt Field-Effect Transistors

Author

Yang, Gwangseok, Jang, Soohwan, Ren, Fan, Pearton, Stephen J., and Kim, Jihyun

Abstract

The robust radiation resistance of wide-band gap materials is advantageous for space applications, where the high-energy particle irradiation deteriorates the performance of electronic devices. We report on the effects of proton irradiation of β-Ga2O3nanobelts, whose energy band gap is ∼4.85 eV at room temperature. Back-gated field-effect transistor (FET) based on exfoliated quasi-two-dimensional β-Ga2O3nanobelts were exposed to a 10 MeV proton beam. The proton-dose- and time-dependent characteristics of the radiation-damaged FETs were systematically analyzed. A 73% decrease in the field-effect mobility and a positive shift of the threshold voltage were observed after proton irradiation at a fluence of 2 × 1015cm–2. Greater radiation-induced degradation occurs in the conductive channel of the β-Ga2O3nanobelt than at the contact between the metal and β-Ga2O3. The on/off ratio of the exfoliated β-Ga2O3FETs was maintained even after proton doses up to 2 × 1015cm–2. The radiation-induced damage in the β-Ga2O3-based FETs was significantly recovered after rapid thermal annealing at 500 °C. The outstanding radiation durability of β-Ga2O3renders it a promising building block for space applications.

Published
2017
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47. Electrical Characteristics of Vertical Ni/?-Ga2O3 Schottky Barrier Diodes at High Temperatures

Author

Oh, Sooyeoun, Yang, Gwangseok, and Kim, Jihyun

Abstract

Vertical geometry b-Ga2O3 Schottky barrier diodes (SBDs) were fabricated and the rectifying forward and reverse current-voltage characteristics were demonstrated at elevated temperatures for a freestanding b-Ga2O3 material with an ultra-wide bandgap of [?]4.9 eV. The breakdown voltage of the fabricated b-Ga2O3 SBDs with a punch-through configuration was [?]210 V without the edge-termination method. The electrical field and potential distributions were numerically simulated with a finite element method. The on-resistance was 2582 O*cm2 at 25degC, and decreased to 0.043 O*cm2 at 225degC. The figure-of-merit (VBR2/Ron) was approximately 17.1 W*cm[?]2. The temperature-dependent Schottky barrier height and ideality factor were also determined. The developed b-Ga2O3 SBDs with the punch-through structure exhibit great potential for high power and high temperature applications.

Published
2017

48. Study on Effect of Proton Irradiation Energy in AlGaN/GaN Metal-Oxide Semiconductor High Electron Mobility Transistors

Author

Ahn, Shihyun, Dong, Chen, Zhu, Weidi, Kim, Jae, Hwang, Hsi, Ren, Fan, Pearton, Stephen J., Yang, Gwangseok, Kim, Jihyun, and Kravchenko, Ivan

Abstract

The effects of proton irradiation energy on Al2O3/AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMT) were studied. MOSHEMTs were irradiated at different irradiation energies of 5 MeV, 10 MeV, or 15 MeV with a fixed proton dose of 5 x 1015 cm-2. After the 5 MeV, 10 MeV and 15 MeV proton irradiation, MOSHEMTs' saturation current at gate voltage of 1V were reduced by 95.3, 68.3 and 59.8% and maximum transconductance were reduced by 88, 54.4, and 40.7% respectively. The carrier removal rate of the irradiation energy employed in this study was in the range of 127-289 cm-1, having lower energy with the highest removal rate.

Published
2015

49. Effect of Proton Irradiation on DC Performance and Reliability of Circular-Shaped AlGaN/GaN High Electron Mobility Transistors

Author

Hwang, Hsi, Hsieh, Ling, Li, Shun, Ren, Fan, Pearton, Stephen J., Patrick, Erin, Law, Mark E, Yang, Gwangseok, Kim, Yeol, Kim, Jihyun, Baca, Albert G., Allerman, Andrew A., and Sanchez, Carlos

Abstract

The effect of 5 MeV proton irradiation on DC performance and reliability of circular-shaped AlGaN/GaN high electron mobility transistors were investigated. The drain saturation current (IDSS) reduced 12.5% and the sheet resistance increased 9.2% after irradiation with a dose of 2x1014 1/cm2. Threshold voltage shifted more positively with a dose of 2x1014 1/cm2 compared to 2x1013 /cm2. Besides, the breakdown voltage improved 39.8% after irradiation with dose of 2x1014 1/cm2. Simulation was done and the peak electric field at the drain side of the gate edge was found to be reduced after irradiation. The defects generated after irradiation at the AlGaN/GaN interface create a virtual gate and thus reduce the electric field. Gate lag measurement was performed to characterize the defects. The current dispersion of DC to high frequency indicates the defects had been generated after irradiation, which is in agreement with the simulation data.

Published
2014

50. CdCl2 Activation Annealing of CdTe Microwires Grown by Close-Spaced Sublimation Method

Author

Yang, Gwangseok, Jung, Younghun, Chun, Seungju, Kim, Donghwan, and Kim, Jihyun

Abstract

We report on the effect of CdCl2 treatment on CdTe microwires that were grown using a simple close-spaced sublimation method. Au particles were used for catalytic vapor-liquid-solid growth of the CdTe microwires with a direct band-gap of [?]1.49 eV. The optical, morphological and structural properties of the CdTe microwires were characterized after post-growth CdCl2 treatment at 385degC for 15 [?] 90 min by scanning electron microscopy, X-ray diffraction, u-Raman scattering, u-photoluminescence spectroscopy and focused-ion-beam techniques. New grains nucleated at the surface of CdTe microwires were observed after CdCl2 treatment. The orientations of the CdTe microwires and of the underlying CdTe thin films became more randomized with increasing durations of CdCl2 treatment. However, the optical properties were hardly affected by CdCl2 treatment. Post-growth CdCl2 activation on CdTe microwires is a critical process for high efficiency CdTe microwire-based solar cells.

Published
2014

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