Metal-assisted photochemical etching of GaN nanowires: The role of metal distribution

Abstract

Metal-assisted chemical etching plays a critical role in synthesizing GaN nanowires. In this work, GaN films grown on Si(111) substrates are immersed in CuSO4/HF etchant under UV illumination to fabricate nanowires. These GaN nanowires are much more homogeneous than those synthesized in AgNO3/HF etchant. During the etching process, Cu and Ag particles appear primarily at the cracks in GaN films where the atoms are more reactive. After that, Cu accumulates continuously at the cracks, while Ag dendrites are formed and spread all over the whole GaN surface. These phenomena are ascribed to the different nucleation rates and diffusion rates of Ag and Cu. The metal particles thus formed block out ultraviolet illumination, and suppress the etching of GaN. It is the orderly accumulation of Cu particles that enables uniform photochemical etching. Our work proposes a novel metal-assisted photochemical etching method for synthesizing uniform GaN nanowires and reveals the physical distribution of the metal during etching. This method has the potential for rapid preparation of GaN nanowires.