Browsing by Author "Ang, Kah-Wee"

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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
;
Gu, Hong
;
Li, Kuilong
;
Guo, Lunchun
;
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).
Large-Scale Transparent Molybdenum Disulfide Plasmonic Photodetector Using Split Bull Eye Structure
(2018-10-18)
Sourav, Adhikary
;
Li, Zhiwen
;
Huang, Zhonghui
;
Botcha, Venkata Divakar
;
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
;
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