The VGF-method was applied for the growth of Si-doped GaAs crystals of 7.5- and 10-cm diameter (n > 1018/cm3). When the average dislocation density in these crystals fell below 200/cm2, the stress-induced 60° dislocations disappeared and other dislocation types predominated in the crystal. These remaining dislocations were classified and the conditions for their occurrence were analyzed. Close to the crystal axis, dislocation walls were found which extended along [110]- and [1¯10]-directions and grew through the whole crystal. These walls were formed by edge dislocations belonging to the (110)½[¯110]- or the (¯110)|[110]-glide system. Apart from the dislocation walls, a dislocation arrangement in the form of a cross was observed in Si-doped GaAs. The orientation of the Burgers vector relative to the dislocation line of this dislocation type was determined. They included an angle close to 45°. Dislocations of this type belonged to the (010)½[101] or the (010)½[10¯1]-glide system. The examination of the growth in the seed well showed that the dislocation structures found in the crystal were already partly formed in the seed well. The growth in the seed well led to a reduction in the etch-pit density although the solid/liquid interface was concave. A reduction in the etch-pit density in the seed well was brought about by the annihilation of dislocations.

Investigation of Residual Dislocations in VGF-Grown Si-Doped GaAs. B.Birkmann, J.Stenzenberger, M.Jurisch, J.Härtwig, V.Alex, G.Müller: Journal of Crystal Growth, 2005, 276[3-4], 335-46