Reactive ion beam etching of GaN and AlGaN/GaN for nanostructure fabrication using methane-based gas mixtures

The basic etching characteristics of electron cyclotron resonance reactive ion beam etching (ECR-RIBE) of GaN and AlGaN/GaN using methane-based mixtures have been studied in view of application to nanostructure fabrication. GaN could be etched by using a gas mixture of CH4/H2/Ar at a rate of about 10nm/min, which is suitable for nanostructure fabrication. The etching process was also applicable to the standard AlGaN/GaN heterostructure. Etching along (1¯100) and (21¯1¯0) stripe patterns revealed {011¯1} and {112¯1} sidewall facets, respectively, indicating that the etching is a facet-revealing process, being dominated by chemical reactions with low physical damage. However, the etching depth showed anomalous saturation at 400-500 nm, and the roughness of the surface increased with time. An in situ X-ray photoelectron spectroscopy (XPS) study detected the formation of Ga droplets. By adding N2 into the gas mixture, Ga droplet formation was suppressed, etch depth saturation disappeared and a smooth etched surface was obtained. Using the optimized etching conditions with N2 addition, an AlGaN/GaN nanowire structure with a wire width of 110nm has been successfully fabricated. © 2002 The Japan Society of Applied Physics.