Surface charge lithography for GaN micro- and nanostructuring

Abstract

We demonstrate the possibility for controlled micro- and nanostructuring of GaN layers by low-dose focused-ion-beam (FIB) treatment with subsequent photoelectrochemical (PEC) etching. The proposed novel maskless approach based on ultra-fast direct writing of surface negative charge that shields the material against PEC etching allows one to fabricate GaN nanowalls and nanowires with lateral dimensions as small as 100 nm. Compared with commonly used lithography masks and/or FIB etching approaches for patterning GaN, the surface charge lithography enables one to fabricate high-aspect ratio micro- and nanostructures and mitigates the need for additional mask layers on the surface prior to etching, and is much faster than FIB etching alone reducing furthermore the ion exposure of material and therefore reducing ion beam damage. We show, in particular, the possibility to etch voids in between structures as narrow as 200 nm and to fabricate GaN suspended membranes and sub-micrometer hollow squares with the thickness defined by the main projection range of implanted ions. The obtained results demonstrate the feasibility of maskless device fabrication based on low-dose FIB direct writing with subsequent wet etching.