SYNCHROTRON TOPOGRAPHIC STUDY OF DEFECTS IN LIQUID-ENCAPSULATED CZOCHRALSKI-GROWN SEMIINSULATING GALLIUM-ARSENIDE WAFERS

Semi-insulating liquid-encapsulated Czochralski-grown undoped GaAs waf ers are investigated by making section and large-area synchrotron topo graphs. The results are compared with optical micrographs taken from a cleaved edge of the wafer. A three-dimensional cellular structure is observed. The diameter of a cell is typically 300-500 mum. The cell wa lls consist of dislocations, which have a [011] preferred direction. T heir Burgers vector is [101BAR] and their glide plane is {111BAR}. Ars enic precipitates, the density of which is about 108 cm-3, decorate th e dislocations. Not all the dislocations form a cellular structure. So me of them are several millimetres long in the same [011] direction as those of the cell walls. Others are parallel to the flat and in the p lanes which form an angle of 50-degrees with the wafer surface.