The crystal quality of III-V substrates was studied by x-ray asymmetric crystal topography (ACT). An extensive study of device-quality GaAs (LEC SI, LEC n-type, VGF and VB) and InP (LEC n-type (S) and SI (Fe) ) wafers reveals that they can contain various defects: low angle grain boundaries, dislocation cell structure, slip, swirl and included mosaic structure.
The high angular resolution of ACT was used to non-destructively study both the epitaxial layer and the substrate. Topographs of the substrate and the epitaxial layers of AlGaAs/GaAs layers grown by MBE and MOCVD are compared. The quality of the substrate has direct implications for the quality of the epitaxial growth. For coherent layers, both the large scale and small scale defects observed in the substrates were exactly reproduced in the epitaxial layers grown by both techniques.