Investigation of the properties and formation process of a peculiar V-pit in HVPE-grown GaN film

Hexagonal V-pits with an inverted pyramid shape appear on the surface of a GaN film after etching by hot H₃PO₄. A regular structure that is different from the V-pit morphology is observed in the cathodoluminescence image. The carrier concentration and stress distributions are nonuniform inside the V-pit. Furthermore, no dominant dislocations or defects are observed in the facets or bottom area of the V-pits. An island coalescence process is considered to contribute to the formation of such V-pits, with the coalesced island facets changing from {1 0 1 m} to {1 1 2 m} at a concave state for the different growth velocities.