Analysis of thermal-treatment-induced dislocation bundles in GaAs wafers by means of X-ray transmission topography and complementary methods

Abstract

By means of a heat treatment that was part of a molecular beam epitaxy (MBE) growth procedure, dislocation bundles have been induced in two-inch-diameter undoped (001) GaAs substrates. On the basis of contrast variations in synchrotron-based single-crystal X-ray transmission topograms that were recorded under conditions of high anomalous transmission, these dislocation bundles have been classified into three different types. Dislocation bundles of the majority type start at the sample edges in regions around the four 〈100〉 peripheral areas, glide typically up to about 1.5 cm into the bulk of the wafer following perpendicular 〈110〉 line directions, and form a pseudo-symmetric fourfold set. There are dislocations with two different Burgers vectors in each majority-type dislocation bundle and the extended segments of all of these dislocations are of the 60° type. In order to explain complementary experimental results, it is suggested that dislocation pairs are formed in the majority-type dislocation bundles. Theoretical support for this hypothesis is derived from a model of plastic deformation of GaAs wafers during typical MBE growth. Dislocation bundles of two minority types, on the other hand, are not part of the fourfold set and originate in peripheral areas at and around 〈110〉.