Optical anisotropy and strain-induced birefringence in dislocation-free silicon single crystals

Birefringence measurements, using a scanning infrared polariscope (SIRP) with high sensitivity, have been carried out in as-grown dislocation-free silicon single crystal ingots. A small amount of birefringence due to 〈110〉 optical anisotropy, which is predicted not by the classical optics theory but by the Lorentzʹs spatial dispersion theory, is observed in the θ–Z optical configuration, for which a probing polarized light is introduced from the as-grown cylindrical ingot surface and then the polarization of the light transmitted through the opposite surface is analyzed. On the other hand, in the R–θ optical configuration, for which the probing polarized light is introduced along the 〈001〉 crystal growth direction from the (001) sliced and polished surface and then the polarization of the light transmitted through the opposite (001) surface is analyzed, the birefringence is still observed although it is extremely small. It is found that this 〈001〉 optical anisotropy is not constant over the (001) cross-section of the ingot but consists of two different components, i.e. a symmetric component distributed over the whole sample, probably caused by point defects, and an asymmetric component distributed randomly near the peripheral region, related to dents and chips on the as-grown cylindrical surface.