Lithographic sonication patterning of large area GaN nanopillar forests grown on a Si substrate

This paper presents lithographic sonication patterning, a highly-scalable, material-independent method for patterning nanopillar forests. Through contact lithography, patterns with dimensions down to 3μm were written across a 3-inch silicon wafer with a gallium nitride nanopillar forest grown through molecular beam epitaxy. Standard, ultraviolet lithography techniques were used to define a photoresist mask that protects covered nanopillars. Exposed nanopillars are removed via local cavitation in a deionized water ultrasonic bath. Sonication strips nanopillars 100nm from their base, thus enabling further processing steps, including metal evaporation and substrate etching. As an example application, a four-point conductivity test device is demonstrated, where lithographic sonication patterning enables smooth, Ohmic contacts and successful dry etching of the silicon device layer. This method is compatible with commonly available cleanroom tools and provides a readily available alternative to more complicated fabrication approaches, such as selective nanopillar growth.