Browsing by Author "Li, Dabing"

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Analysis of the back-barrier effect in AlGaN/GaN high electron mobility transistor on free-standing GaN substrates
(2020-01-25)
Liu, Xinke
;
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.
Nearly lattice-matched molybdenum disulfide/gallium nitride heterostructure enabling high-performance phototransistors
(2019-03-01)
Liu, Xinke
;
Chen, Yuxuan
;
Li, Dabing
;
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
Vertical GaN-on-GaN PIN diodes fabricated on free-standing GaN wafer using an ammonothermal method
(2019-10-05)
Chen, Sung-Wen Huang
;
Wang, Hao-Yu
;
Hu, Cong
;
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.