Browsing by Author "Tu, S. J."

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Characterization of n-GaN with Naturally Textured Surface for Photoelectrochemical Hydrogen Generation
(2010)
Liu, Shu-Yen
;
Sheu, J. K.
;
Ye, Jhao-Cheng
;
Tu, S. J.
;
Hsu, Che-Kang
To reduce light reflection and enlarge the effective reaction surface area at the n-GaN/electrolyte interface, n-GaN epitaxial layers with naturally textured surface are utilized. The layers are combined with Cr/Au ohmic contacts on n-GaN to form working electrodes that generate hydrogen by direct photoelectrolysis of water. Although the surface reflection on the naturally textured n-GaN samples is lower than that on n-GaN epitaxial layers with flat surface, our results reveal that the photocurrent (I(ph)) and gas generation rates (R(gas)) obtained from the naturally rough n-GaN samples are lower than those from the flat samples. The results can be attributed to the fact that the rough n-GaN surface caused by dense surface pits leads to significant recombination of photogenerated carriers with charged defects; this occurs before carriers reach the ohmic contacts, thereby resulting in lower I(ph) and R(gas). Related analyses have been performed and presented in this paper to initially explain the possible mechanism. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3499327] All rights reserved.
Improved Power Conversion Efficiency of InGaN Photovoltaic Devices Grown on Patterned Sapphire Substrates
(2011-04-01)
Yang, C. C.
;
Sheu, J. K.
;
Kuo, C. H.
;
Huang, M. S.
;
Tu, S. J.
The InGaN/sapphire-based photovoltaic (PV) cells with Al(0.14)Ga(0.86)N/In(0.21)Ga(0.79)N superlattice structures that serve as absorption layers were grown on patterned sapphire substrates (PSSs). Under global air-mass 1.5 conditions, the short-circuit current density, the open-circuit voltage, and the fill factor obtained from the PV cells were 1.21 mA/cm(2), 2.18 V, and 0.65, respectively, corresponding to a conversion efficiency of 1.71%. Compared with PV devices grown on flat sapphire substrates, the photocurrent of PSS-grown PV devices was enhanced by 26%. The improved PV performance was attributable to the positive effects of the PSS on the material quality.