Single crystals of Si-doped material, with extremely low dislocation densities (etch pit density of 50 to 1000/cm2), were grown by using the vertical gradient freeze method. The crystals were characterized by means of white-beam X-ray diffraction topography and infra-red transmission microscopy. It was found, with decreasing dislocation density (etch pit density below 200/cm2), that dislocations having a line vector that was parallel to the [001] growth direction of the crystals became more and more predominant. These residual dislocations were introduced by the seeding process. Such residual dislocations could not be avoided by minimizing thermal stress during crystal growth.

Analysis of types of residual dislocation in the vertical gradient freeze growth of GaAs J.Amon, J.Härtwig, W.Ludwig, G.Müller: Journal of Crystal Growth, 1999, 198-199[1-4], 367-73