The optimum choice of reflexion to reveal dislocations in gallium arsenide by X-ray reflexion topography

Single-crystal reflexion topographs from various planes in gallium arsenide are presented and the contrast is compared, in some cases, with double-crystal topograph equivalents. Theory is presented to explain the numerous effects observed but principally the lack of contrast when the absorption distance is small. This aspect of reflexion theory is combined with an evaluation of the effective tilt round a dislocation at various depths below the surface. Tables are also presented giving good and bad choices of reflecting planes for single-crystal topography in gallium arsenide.