Investigation of residual dislocations in VGF-grown Si-doped GaAs

The VGF-method was applied for the growth of Si-doped GaAs crystals of 3 and 4 inch diameter (n > 10(18) cm(-1)). When the average dislocation density in these crystals falls below 200 cm(-2) the stress-induced 60 degrees-dislocations disappear and other dislocation types dominate the crystal. These remaining dislocations are classified and the conditions for their occurence are analyzed. Close to the crystal axis, dislocation walls are found which extend along [110]- and [1 (1) over bar0]-directions and grow through the whole crystal. These walls are formed by edge dislocations belonging to the (110)(1)/(2)[(1) over bar 10] - or the ((1) over bar 10) (1)/(2)[110]-glide system. Apart from the dislocation walls, a dislocation arrangement in the form of a cross is observed in Si-doped GaAs. The orientation of the Burgers, vector relative to the dislocation line of this dislocation type was determined. They include an angle close to 45 degrees. Dislocations of this type belong to the (010)(1)/(2)[101] or the (010)(1)/(2)[10 (1) over bar]-glide system. The examination of the growth in the seed well shows that the dislocation structures found in the crystal are partly already formed in the seed well. The growth in the seed well leads to a reduction of the EPD although the solid-liquid interface is concave. A reduction of the EPD in the seed well is accomplished by annihilation of dislocations. (c) 2004 Elsevier B.V. All rights reserved.