Synchrotron topographic study of defects in liquid-encapsulated Czochralski-grown semi-insulating gallium arsenide wafers

Semi-insulating liquid-encapsulated Czochralski-grown undoped GaAs wafers are investigated by making section and large-area synchrotron topographs. 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 μm. The cell walls consist of dislocations, which have a 〈011〉 preferred direction. Their Burgers vector is 〈10ī1〉 and their glide plane is {1ī11}. Arsenic precipitates, the density of which is about 10 8 cm -3 , decorate the dislocations. Not all the dislocations form a cellular structure. Some 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 planes which form an angle of 50° with the wafer surface.