Browsing by Author "Liu, Xinke"

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AlGaN/GaN high electron mobility transistors with a low sub-threshold swing on free-standing GaN wafer
(2017-09-01)
Liu, Xinke
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Gu, Hong
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Li, Kuilong
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Guo, Lunchun
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Zhu, Deliang
This paper reported AlGaN/GaN high electron mobility transistors (HEMTs) with low sub-threshold swing SS on free-standing GaN wafer. High quality AlGaN/GaN epi-layer has been grown by metal-organic chemical vapor deposition (MOCVD) on free-standing GaN, small full-width hall maximum (FWHM) of 42.9 arcsec for (0002) GaN XRD peaks and ultralow dislocation density (similar to 10(4)-10(5) cm(-2)) were obtained. Due to these extremely high quality material properties, the fabricated AlGaN/GaN HEMTs achieve a low SS (similar to 60 mV/decade), low hysteresis of 54 mV, and high peak electron mobility mu(eff) of similar to 1456 cm(2)V(-1)s(-1). Systematic study of materials properties and device characteristics exhibits that GaN-on-GaN AlGaN/GaNHEMTsare promising candidate for next generation high power device applications. (C) 2017 Author(s).
Analysis of the back-barrier effect in AlGaN/GaN high electron mobility transistor on free-standing GaN substrates
(2020-01-25)
Liu, Xinke
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Wang, Hao-Yu
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Chiu, Hsien-Chin
;
Chen, Yuxuan
;
Li, Dabing
The effect of AlGaN back-barrier on AlGaN/GaN high electron mobility transistors (HEMTs) using freestanding GaN wafer has been investigated in this work. With the introducing back-barrier structure, the leakage path underneath the buffer (native nitrogen-vacancies and GaOx compounds of the HVPE-grown free-standing GaN surface) layer can be suppressed by lift-up the conduction band. As compared with AlGaN/GaN HEMTs on SiC wafer, AlGaN/GaN HEMTs on free-standing GaN wafer show enhanced drain current ( 700 mA/mm), improved transconductance (143 mS/mm), less current collapse (12%), higher current gain cut-off frequency (13 GHz), and maximum stable gain cut-off frequency (24 GHz), which is attributed to the higher epi quality layer on free-standing GaN wafer. (C) 2019 Elsevier B.V. All rights reserved.
GaN Schottky Barrier Diodes on Free-Standing GaN Wafer
(2017-01-01)
Liu, Xinke
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Gu, Hong
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Li, Kuilong
;
Wang, Jianfeng
;
Wang, Lei
In this paper, vertical GaN Schottky barrier diodes (SBDs) have been demonstrated on the freestanding (FS) GaN wafer. Room temperature photoluminescence shows no emission of yellow luminescence, due to the eliminating the point defects (O-N, V-Ga). The average full width half maximum (FWHM) value of.-scans for (0001) and (10-12) planes is 53 and 103 arcsec, respectively, as measured by high resolution X-ray diffraction; the average dislocation density at the top surface measured by cathodoluminescence is similar to 7.7 x 10(5) cm(-2). The vertical GaN SBDs fabricated on this FS-GaN wafer achieve a breakdown voltage of 1200 V, an on-state resistance R-on of 7 m Omega.cm(2), and a current on/off ratio I-on/I-off of similar to 2.3 x 10(10), which leads to a power device figure-of-merit V-BR(2)/R-on of 2.1 x 10(8) V-2 Omega(-1) cm(-2). TCAD simulation was employed to study the device breakdown mechanism, and shows the breakdown mechanism is due to the impact ionization at the edge of the Schottky gate. (c) 2017 The Electrochemical Society. All rights reserved.
Large-Scale Transparent Molybdenum Disulfide Plasmonic Photodetector Using Split Bull Eye Structure
(2018-10-18)
Sourav, Adhikary
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Li, Zhiwen
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Huang, Zhonghui
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Botcha, Venkata Divakar
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Hu, Cong
A high performance photodetector array on transparent substrate is highly sought after for enabling next-generation imaging technology at the visible wavelengths. 2D materials such as molybdenum disulfide (MoS2) are attractive for such application owing to its superior optoelectronic properties and transparency when scaled to atomic thinness. Here, direct growth of MoS2 on centimeter-scale transparent Al2O3 substrate is reported using a high yield and scalable chemical vapor deposition approach. This enables a large area photodetector array to be demonstrated, wherein aluminum split bull eye (SBE) plasmonic structure is integrated to achieve further performance boost due to surface plasmon resonance (SPR) effect. For a wavelength of 405 nm, the plasmonic MoS2 detector achieves an ultralow noise equivalent power of approximate to 6.2 x 10-14 W Hz(-1/2) and a high responsivity of 7.26 A W-1 at a small bias of 1.0 V, which is more than 6x larger than the reference detector due to SPR effect. Finite-difference time-domain simulation confirms a higher concentration of optical field distribution at the center of the SBE structure, which is responsible for the enhancement of photocurrent and sensitivity even at low-light condition.
Nearly lattice-matched molybdenum disulfide/gallium nitride heterostructure enabling high-performance phototransistors
(2019-03-01)
Liu, Xinke
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Chen, Yuxuan
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Li, Dabing
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Wang, Sheng-Wen
;
Ting, Chao-Cheng
Molybdenum disulfide (MoS2)-based phototransistors are attractive for optical electronics in a large-scale size, such as transparent touch screens. However, most of the work done over the past decade has been on an opaque SiO2/Si wafer with a small size (micrometer to millimeter). In this work, a large-scale multilayer MoS2-based phototransistor has been fabricated on a transparent freestanding gallium nitride (GaN) wafer using a scalable chemical vapor deposition method. Due to the near lattice match and small thermal expansion mismatch between GaN and MoS2, the as-grown multilayer MoS2-on-GaN film shows high material quality in terms of low full width at half-maximum (similar to 5.16 cm(-1)) for the E-2g(1) Raman mode and a high absorption coefficient (similar to 10(6) cm(-1)) in the wavelength range of 405-638 nm. Under a wavelength of 405 nm at an incident power of 2 mWand applied voltage of 9 V, the fabricated MoS2-on-GaN phototransistor achieved a maximum responsivity of 17.2 A/W, a photocurrent gain of 53.6, and an external quantum efficiency of 5289%, with specific detectivity (similar to 10(10)-10(12) Jones) and low noise equivalent power (10(-12)-10(-14) W/Hz(1/2)) in the visible range of 405-638 nm. A typical response time of 0.1-4 s in the ambient air has also been recorded for the demonstrated MoS2-on-GaN phototransistor. Our work paves a technologic stepping stone for MoS2-based phototransistors for multifunctional transparent and touch-based optoelectronics in the future. (C) 2019 Chinese Laser Press
Research on a Novel GaN-Based Converted Mini-LED Backlight Module via a Spectrum-Decouple System
(2020-01-01)
Huang, Che-Hsuan
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Chang, Shu Hsiu
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Liaw, Been-Yu
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Liu, Cheng-Yi
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Chou, Chia-Yueh
Owing to the development of modern display technology, micro- and mini-light-emitting diodes (LEDs) have affected technological advancements in the display industry. The structure of mini-LEDs is completely different than that of traditional LED backlights because the former employs a display technology with an LED array structure, optical resonant cavity, and color conversion layer. Display backlight technology encounters difficulty in achieving a truly effective energy-loss mechanism when designing or measuring mini-LED performance. The present study proposes three major mini-LED energy loss mechanisms: cross-talk, resonant, and quantum conversion losses. Herein, the spectrum was obtained through the integrating sphere system, and the calculation mechanism was formed by the down-conversion theorem as the decoupling principle, which successfully calculated the independent energy-loss efficiency of each mechanism and effectively deduced the brightness and color saturation performance of this design combination.
Vertical GaN-on-GaN PIN diodes fabricated on free-standing GaN wafer using an ammonothermal method
(2019-10-05)
Chen, Sung-Wen Huang
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Wang, Hao-Yu
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Hu, Cong
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Chen, Yong
;
Wang, Hao
We report vertical GaN-on-GaN PIN diodes with a record high figure-of-merit (V-BR(2)/R-on) of 29.7 GW/cm(2) on free-standing GaN wafer using a complementary metal-oxide-semiconductor (CMOS) compatible contact materials. Due to the low substrate resistivity, low contact resistance, and high quality of GaN drift layer, a low on-state resistance R(on )of 0.31 m Omega cm(2) is obtained. With integrating of the metal filed plate structure in the vertical device, the peak electrical field along the GaN mesa edge can be significantly reduced, thus leading to a high breakdown voltage V-BR of 3.04 kV. The vertical GaN-on-GaN PIN diodes in this work show turn-on voltage V-on of similar to 3.4 V, on/off current ratio of similar to 1.3 x 10(7), and ideal factor n of similar to 2.2. According to the reverse switching measurement, the reverse recovery time T-rr. (reverse recovery charge Q(rr)) is 22.8 ns (4.8 nC) and 24.0 ns (5.4 nC), respectively, under a testing temperature of 300 K and 500 K. (C) 2019 Elsevier B.V. All rights reserved.