Direct measurement of twist mosaic in GaN epitaxial films as a function of growth temperature

Direct measurements of the mosaic twist in GaN films have been carried out using grazing incidence in-plane x-ray diffraction (GIIXD) on a commercially-available diffractometer in the laboratory. The GaN 11.0 in-plane diffraction was measured to obtain the twist mosaic directly, while the GaN 00.2 surface-symmetric rocking curve was used to measure the tilt mosaic. For GaN growth temperatures between 1002 deg. C and 1062 deg. C, the tilt mosaic decreased monotonically with increased temperature, while the twist mosaic showed a minimum at 1022 deg. C, a temperature previously selected empirically as giving the best device yield and optimum optical domain size. A substantial fall in twist and tilt mosaic was observed on annealing of the nucleation layers, the lowest twist mosaic occurring at an annealing temperature of 1002 deg. C, where it was almost equal to the tilt mosaic. A weak minimum in the tilt mosaic variation was seen at an annealing temperature of 1023 deg. C