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. (C) 2000 American Institute of Physics. [S0003-6951(00)04827-0].