Enhancement of the energy photoconversion efficiency through crystallographic etching of a c-plane GaN thin film

Using a simple and inexpensive crystallographic etching technique on a GaN thin film, the energy photoconversion efficiency was increased by 100%. Prior to etching, the thin film's solar-to-hydrogen conversion efficiency at the applied bias of 0.5 V versus the counter electrode in 1.0 M HCl solution was 0.37%. After etching, the efficiency doubled to 0.75%. After five hours of continuous gas collection, the unetched GaN thin film yielded a stable photocurrent of 0.41 mA cm-2 which produced 0.10 mL of H2 gas. The etched sample, on the other hand, resulted in an improved stable photocurrent of 0.83 mA cm-2 and yielded a greater volume of 0.70 mL of H2 gas, with the presence of H2 confirmed through gas chromatography. Further investigations have shown that the increased hydrogen generation capacity was possibly caused by three factors: one, increase in surface area caused by the etching process; two, decrease in surface donor concentration caused by the etching as probed through Mott-Schottky plots; and three, the appearance of stepped edges and etched facets that show greater photocatalytic activity than the original c-plane when probed through the photodeposition of Ag particles. © 2010 The Royal Society of Chemistry.