Browsing by Author "Wang, Hsiang-Chen"

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Influences of Contact Metals on the Performances of MoS2 Devices under Strains
(2019-12-19)
Tseng, Sian-Hong
;
Chen, Hung-Yi
;
Hsu, Wei-Ting
;
Wang, Hsiang-Chen
;
Li, Yuan-Yao
The growth of large-area MoS2 films was achieved through atmospheric pressure chemical vapor deposition via vapor management in this study. The thickness of the MoS2 film changed upon varying the amount of vapor deposited on the substrate. Gratifyingly, large-area monolayer MoS2 was obtained under controlled conditions. Studies using transmission electron microscopy and second harmonic generation confirmed that the MoS2 films were composed of grains having sizes ranging from 40 to 70 mu m. Flexible MoS2 device arrays were fabricated on a polyimide substrate; the device arrays displayed high spatial uniformity in their carrier transport properties. The contact metals affected the electrical characteristics of the MoS2 devices under strain; the sensitivity of devices featuring Schottky contacts was higher than that of those with ohmic contacts. Importantly, the device arrays exhibit sensitive and endurance performances under strain cycles of up to 10(5) times. These results suggest a means for the feasible growth of large-area single-layer MoS2 films, as well as the exploitation of flexible MoS2 device arrays in strain and human motion sensor applications.
Nanoparticle-Doped Polydimethylsiloxane Fluid Enhances the Optical Performance of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes
(2019-07-15)
Ye, Zhi Ting
;
Pai, Yung-Min
;
Lin, Chih-Hao
;
Chen, Lung-Chien
;
Hong Thai Nguyen
This paper proposes a new encapsulation structure for aluminum nitride-based deep UV light-emitting diodes (DUV-LEDs) and eutectic flip chips containing polydimethylsiloxane (PDMS) fluid doped with SiO2 nanoparticles (NPs) with a UV-transparent quartz hemispherical glass cover. Experimental results reveal that the proposed encapsulation structure has considerably higher light output power than the traditional one. The light extraction efficiency was increased by 66.49% when the forward current of the DUV-LED was 200mA. Doping the PDMS fluid with SiO2 NPs resulted in higher light output power than that of undoped fluid. The maximum efficiency was achieved at a doping concentration of 0.2wt%. The optical output power at 200mA forward current of the encapsulation structure with NP doping of the fluid was 15% higher than that without NP doping. The optical output power of the proposed encapsulation structure was 81.49% higher than that of the traditional encapsulation structure. The enhanced light output power was due to light scattering caused by the SiO2 NPs and the increased average refractive index. The encapsulation temperature can be reduced by 4 degrees C at a driving current of 200mA by using the proposed encapsulation structure.
The action of silicon doping in the first two to five barriers of eight periods In0.2Ga0.8N/GaN multiple quantum wells of blue LEDs
(2016-09)
Chen, Meng-Chu
;
Cheng, Yung-Chen
;
Huang, Chun-Yuan
;
Wang, Hsiang-Chen
;
Lin, Kuang-I
First two to five barriers in the growth sequence having silicon (Si) doping of eight periods In0.2Ga0.8N/GaN quantum wells (QWs) on twenty pairs of In0.02Ga0.98N/GaN superlattice strain relief layers (SRLs) of blue LEDs were prepared by low pressure metal-organic chemical vapor deposition (LPMOCVD) system on patterned sapphire substrates (PSSs). The effect of doping layers on the luminescence properties of QWs of blue LEDs was investigated. For the sample with first four barriers having Si doping, formation of soft confinement of QWs potential and strong carrier localization inside QWs were occurred. There is better spread of carriers among eight QWs and strong radiative recombination of carriers inside QWs. The increase of output power and external quantum efficiency (EQE) is due to decrease of Auger processes, leakage of carriers out of QWs, and nonradiative recombination centers. The consequences demonstrate that first four barriers with Si doping possess the favorable doping condition for eight periods In0.2Ga0.8N/GaN QWs. (c) 2016 Elsevier B.V. All rights reserved.