The growth of facets and the generation of twins, on the <100> faces of crystals which were prepared by using the vertical gradient freezing technique, were investigated by using chemical etching, photo-etching, and X-ray topographic techniques. It was found that, due to the polarity of the (111) plane, the As facets were larger and more irregular than were Ga facets, while the twins always appeared on As facets. The twins nucleated at a change in boundary condition which was caused by the temperature gradient and crucible shape. The generation of twins was explained with regard to the edge concavity at the solid/liquid interface, and the supercooling which was required for the initial nucleation of a facet. It was noted that twins were produced more often in Si-doped crystals than in undoped ones.

H.J.Koh, M.H.Choi, I.S.Park, T.Fukuda: Crystal Research and Technology, 1995, 30[3], 397-403