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 m ulti-step annealed in holders of different geometry was characterized by th e scanning infrared polariscope (SIRP) method. The SIRP maps reveal that th e distribution of strain is significantly influenced by the symmetry of ann ealing, 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 resid ual 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 gr aphite. Temperature gradients up to 30 K cm(-1) were measured depending upo n the rates of cooling and heating. (C) 1999 Elsevier Science S.A. All righ ts reserved.