Study on material removal mechanisms in electrochemical etching-enhanced polishing of GaN

Abstract

Electrochemical etching has been proven to be a highly effective method for the removal of GaN materials. In this work, the material removal mechanisms in electrochemical-enhanced polishing process are studied from two aspects: carrier behavior and mechanical removal. It is found that the distribution of carriers can be altered along the polar plane by the electric field during electrochemical etching and will not recover spontaneously. A layer of excess carriers would accumulate on the Ga-face after electrochemical etching and cause severe surface oxidation during sample preservation. Additionally, it is revealed that the etched surface morphology can be divided into two types: protrusions and pits, depending on the excessive carrier density. Mechanical polishing is conducted on the pre-etched and non-etched surface, respectively. The pre-etched surface demonstrates better ductility than that of the non-etched surface owing to the formation of porous structure during electrochemical etching. The surface quality is also desirable which is confirmed by the photoluminescence (PL) spectra. The electrochemical etching-enhanced polishing can be considered as a semi-final processing technique that efficiently removes the damaged layer and reduces the surface roughness to sub-nanometer level.