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 H-2 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 H-2 gas, with the presence of H-2 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.