Origin of hexagonal-shaped etch pits formed in (0001) GaN films

We report the origin of hexagonal-shaped etch pits generally observed by conventional wet etching processes on (0001) GaN-based films based on the investigation with transmission electron microscopy on GaN films after being etched with molten KOH. The origin of hexagonal-shaped etch pits is identified as nanopipes through careful characterization of abnormal contrast of nanopipe (open-core screw dislocation), “lobe contrast” of end-on edge and screw (full-core) dislocations, visible and invisible conditions of edge and screw dislocations. Consideration of energetics of these defects also suggests preferential etch pit formation at nanopipes because of much higher energy.