Synchrotron White Beam Topographic Studies of Gallium Arsenide Crystals

A series of samples cut out from different types of gallium arsenide crystals with low dislocation density were studied by means of white beam synchrotron topography. The investigation was performed with transmission and back-reflection projection methods and transmission section method. Some of the topographs in transmission geometry provided a very high sensitivity suitable for revealing small precipitates. The transmission section images significantly differed depending on the wavelength and absorption. In some cases a distinct Pendellösung fringes and fine details of dislocation and precipitates images were observed. It was possible to reproduce the character of these images by means of numerical simulation based on integration of Takagi-Taupin equations. Due to more convenient choice of radiation, synchrotron back-reflection projection topography provided much better visibility of dislocations than analogous methods realized with conventional X-ray sources.