Reactive Ion Beam Etching of GaN and AlGaN/GaN for Nanostructure Fabrication Using Methane-Based Gas Mixtures

Abstract

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 10 nm/min, which is suitable for nanostructure fabrication. The etching process was also applicable to the standard AlGaN/GaN heterostructure. Etching along <1100> and <2110> stripe patterns revealed {0111} and {1121} 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 110 nm has been successfully fabricated.