An X-ray diffractometric study was made of bulk crystals of wurtzite-structured material, with (00•1)-oriented plates, that had been grown by using the high-pressure (12 to 15kbar) high temperature (about 1800K) method. The studies included rocking-curve analyses, reciprocal lattice mapping, topography and lattice parameter measurements. It was found that monocrystals with sizes of up to about 1mm exhibited very high perfection (rocking curves of 20 to 30arcsec). Larger crystals had a mosaic structure (0.1 to 1mm crystallites separated by 1 to 3arcmin angle boundaries) as found using X-ray topography. A model for the creation of these low-angle boundaries was proposed which was based upon the observations that the mosaic crystals were dome-shaped, that the concave side was N-terminated (and grew faster) and that this side had smaller lattice parameters than those of the Ga-terminated side. The decrease in the lattice parameters was attributed to Ga precipitation (observed by electron microscopy) beneath the N-terminated side. The difference in lattice parameters on the 2 sides of the crystal caused a bending which was then relaxed by the creation of low-angle boundaries.

M.Leszczynski, I.Grzegory, H.Teisseyre, T.Suski, M.Bockowski, J.Jun, J.M.Baranowski, S.Porowski, J.Domagala: Journal of Crystal Growth, 1996, 169[2], 235-42