Journal of Crystal Growth, Vol.237, 350-355, 2002
Synchrotron X-ray topography of undoped VCz GaAs crystals
For the first time vapour pressure controlled Czochralski (VCz) monocrystals of semi-insulating (SI) GaAs, grown at IKZ Berlin. have been investigated by synchrotron X-ray topography. The X-ray topographs of a typical VCz sample. taken from the cylindrical part. show dislocation images resembling those of SI vertical gradient freeze-grown GaAs crystals. From the disappearance of the dislocation image in selected topographs it is concluded that the Burgers vector for most dislocations is parallel to <110>. The main part proves to be of 60degrees type. The cellular structure. typical for liquid encapsulated Czochralski material, is not seen in the VCz samples. Large volumes up to 0.5 x 0.5 x 0.5 mm(3) are dislocation-free. The results are compared with etch pit density (EPD) measurements from the same crystals. The average EPD is (1-2) x 10(4) cm(-2). The minimum along <110> is 2 x 10(3) cm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.
Keywords:crystal structure;defects;etching;X-ray topography;liquid encapsulated Czochralski method;vapor pressure controlled Czochralski method;gallium compounds