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°C and 1062°C, the tilt mosaic decreased monotonically with increased temperature, while the twist mosaic showed a minimum at 1022°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°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°C.