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Immersed finger-type indium tin oxide ohmic contacts on p-GaN photoelectrodes for photoelectrochemical hydrogen generation

Shu-Yen Liu, J. K. Sheu, M. L. Lee, Yu-Chuan Lin, S. J. Tu, F. W. Huang, and W. C. Lai

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Abstract

In this study, we demonstrated photoelectrochemical (PEC) hydrogen generation using p-GaN photoelectrodes associated with immersed finger-type indium tin oxide (IF-ITO) ohmic contacts. The IF-ITO/p-GaN photoelectrode scheme exhibits higher photocurrent and gas generation rate compared with p-GaN photoelectrodes without IF-ITO ohmic contacts. In addition, the critical external bias for detectable hydrogen generation can be effectively reduced by the use of IF-ITO ohmic contacts. This finding can be attributed to the greatly uniform distribution of the IF-ITO/p-GaN photoelectrode applied fields over the whole working area. As a result, the collection efficiency of photo-generated holes by electrode contacts is higher than that of p-GaN photoelectrodes without IF-ITO contacts. Microscopy revealed a tiny change on the p-GaN surfaces before and after hydrogen generation. In contrast, photoelectrodes composed of n-GaN have a short lifetime due to n-GaN corrosion during hydrogen generation. Findings of this study indicate that the ITO finger contacts on p-GaN layer is a potential candidate as photoelectrodes for PEC hydrogen generation.

©2012 Optical Society of America

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Figures (4)
Fig. 1
Fig. 1 Schematic diagram of the photoelectrochemical cells (a) PEC1, (c) PEC2. Figure 1(b) shows the schematic structure of ITO/SiO2 staked layers on the p-GaN.

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Fig. 2
Fig. 2 Typical photocurrent density-bias curves of the experimental PEC cells.

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Fig. 3
Fig. 3 Photocurrent and dark current densities as a function of applied bias VCE of PEC1, PEC3, and PEC4.

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Fig. 4
Fig. 4 SEM images of the surface of PEC1 (a) before and (b) after photoelectrochemical measurements. The insets of Fig. 4(a) and 4(b) show the top-view of the AFM images of PEC1 before and after photoelectrochemical measurements, respectively.

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Tables (1)

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Table 1 Critical Bias for Hydrogen Generation of the Experimental PEC Cells

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