Birefringence induced by residual strain in optically isotropic III-V compound crystals

By using a high-sensitivity high-spatial-resolution scanning infrared polariscope, we have quantitatively measured a small amount of birefringence induced by residual strain in commercial wafers of III-V compound crystals. From the measurement results in commercial (100) wafers of GaAs grown by the liquid encapsulated Czhocralski method, it is found that the 2D distribution maps of absolute difference (Delta) n between the principal refractive indices exhibit fourfold symmetry accompanying some fine structure such as stripes or line-segment patterns. The magnitude of (Delta) n is about 5 X 10-5 in maximum and the principal axes of birefringence are approximately radially or tangentially aligned. From the detailed analysis of photoelastic effect on the (100) wafers, the in-plane components of residual strains: Syy - Szz and 2Syz are deduced from the measured (Delta) n and the principal angle of birefringence (psi) .