Formation of large-area GaN nanostructures with controlled geometry and morphology using top-down fabrication scheme

This paper details the fabrication of GaN nanoscale structures using deep ultraviolet lithography and inductively coupled plasma (ICP) etching techniques. The authors controlled the geometry (dimensions and shape) and surface morphology of such nanoscale structures through selection of etching parameters. The authors compared seven different chlorine-based etch chemistries: Cl-2, Ar, Cl-2/N-2, Cl-2/Ar, Cl-2/N-2/Ar, Cl-2/H-2/Ar, and Cl-2/He/Ar. The authors found that nitrogen plays a significant role in fabricating high quality etched GaN nanostructures. This paper presents the effects of varying the etch parameters, including gas chemistry, gas flow rate, ICP power, rf power, chamber pressure, and substrate temperature, on the etch characteristics, including etch rate, sidewall angle, anisotropy, mask erosion, and surface roughness. Dominant etch mechanisms in relation to the observed characteristics of the etched features are discussed. Utilizing such methods, the authors demonstrated the fabrication of nanoscale structures with designed shapes and dimensions over large area. Nanocolumns with diameter of 120 nm and height of 1.6 mu m with sidewall angle of 86 degrees (90 degrees represent a vertical sidewall) were fabricated. Nanocones with tip diameter of 30nm and height of 1.6 mu m with sidewall angle of 70 degrees were demonstrated. Such structures could potentially be used in light-emitting diodes, laser diodes, photodetectors, vertical transistors, field emitters, and photovoltaic devices. This study indicates the feasibility of top-down methods in the fabrication of next-generation nitride-based nanoscale devices, with large-area uniformity and scalability. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4739424]