First direct observation of voids in bulk, undoped, semi-insulating GaAs

Abstract
Defect selective A/B chemical etching, low-temperature scanning cathodoluminescence, and transmission electron microscopy have been used to study the microstructure of undoped, semi-insulating liquid-encapsulated Czochralski GaAs wafers. It is shown for the first time that a distribution of microvoids is present in the bulk material at a number density of at least 1010 cm−3. These microvoids, which are present in the centers of the dislocation cell structures observed in the GaAs, may result from the post-growth heat treatment of ingots which is used to improve the material homogeneity. A possible explanation for the formation of these microvoids is given.