Vacancy Clustering in Dislocation-Free High-Purity Germanium

A germanium crystal of high purity was grown in H2 with a maximum dislocation density of 3000 cm−2, which was estimated by white beam x-ray topography. Due to a dynamical diffraction effect, the topographs revealed the existence of vacancy clusters in the form of voids in dislocation-free parts of the crystal. Etch pit density analysis, the standard technique employed for crystalline wafers to determine dislocation density, failed to reliably represent dislocations in dislocation-free parts of the crystal. On the other hand, we were able to identify a different type of etching pattern for a dislocation-free crystal. Microwave photoconductance decay was utilized to determine the charge carrier lifetime, which was found to be up to 500 μs for regions with dislocations, while being only 100 μs for dislocation-free parts of the crystal.