Microstructural studies on vertical Bridgman crystals (GaAs) by NIR-microscopy and DSL-etching

摘要

The dislocation structure of doped VB-GaAs-crystals has been investigated by NIR-transmission microscopy comparing bright field, phase- and "Schlieren"contrast. It is shown that the image contrast for phase microscopy- as well as for bright field-conditions is caused by a different refractive index which itself is due to a different concentration of free charge carriers in the Cottrell atmosphere. Phase microscopy permits the study of the effect of thermal annealing on individual dislocations and the associated Cottrell atmosphere (e.g. the kinetics of Cottrell atmosphere-formation) in bulk samples.