Photoelastic characterization of residual strain in GaAs wafers annealed in holders of different geometry

The spatial distribution of residual strain in undoped 2 inch GaAs wafers multi-step annealed in holders of different geometry was characterized by the scanning infrared polariscope (SIRP) method. The SIRP maps reveal that the distribution of strain is significantly influenced by the symmetry of annealing, in particular by the points of contact between wafer and holder. In contrast to the as-grown state, the annealed wafers show fine patterns of slip lines. The lowest level and the most homogeneous distribution of residual strain were achieved by annealing in a vertically positioned holder of graphite rings. The radial temperature differences in the wafers caused by heating and cooling were checked by means of thermocouples on dummies of graphite. Temperature gradients up to 30 K cm−1 were measured depending upon the rates of cooling and heating.