P. Etchegoin

Circular birefringence in zinc-blende-type semiconductors

Abstract The existence of two different indices of refraction for left and right circularly polarized light (optical activity) depends, from the macroscopic point of view, on the point group of the lattice which fixes the symmetry of the macroscopic dielectric tensor eα, β(ω, k). The point group of zinc-blende-type materials (Td) does not allow the existence of optical activity. However, by lowering the symmetry by means of an external uniaxial stress along [100] (Td → D2d) optical activity becomes allowed for light propagating with k along [010] or [001], at least in spectral regions where the k independent piezobirefringence is negligible. We have performed experiments, based on transmission of light through crossed polarizers, on GaAs and InP. We show some results and discuss experimental aspects for an ellipsometry-type set-up.

Piezo-optical response of semiconductors

Abstract The effects of uniaxial stress on the optical properties of Si, Ge, GaAs, InP and GaP have been investigated using rotating analyser ellipsometry. Under the presence of an external stress described by the second-rank tensor Xij, changes in the dielectric tensor ϵij(ω) are linked to Xij by the fourth-rank symmetric tensor (piezo-optical tensor) P>ijkl(ω) such that Δϵij(ω) = Pijkl(ω)Xij. For diamond and zinc blende types of semiconductors three independent functions P11(ω), P12(ω) and P44(ω) are required to characterize this tensor fully. Measurements of these functions were performed at room temperature, with the optical path kept in air, in the visible range ( h ω ≈ 1.5–5.4 eV ) and the values compared with extensive existing information (polarized reflectivity and piezoreflectance) as well as calculations with the empirical pseudopotential method. We review the piezoellipsometry technique and present some new results.