Semiconductor photoelastic constants measured by light scattering in superlattices

The technique for the measurement of the photoelastic constants that is based on light scattering (Raman and Brillouin) by superlattice acoustic phonons is refined and applied to ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As and ${\mathrm{Si}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Ge}}_{\mathrm{x}}$ materials. The photoelastic constants of ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As with respect to GaAs and those of ${\mathrm{Si}}_{0.5}$ ${\mathrm{Ge}}_{0.5}$ with respect to Si are measured as a function of the wavelength of the laser excitation. One finds that the photoelastic constant of ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As undergoes a nonlinear variation with the aluminum concentration x and that the ratio of the photoelastic constants of ${\mathrm{Si}}_{0.5}$ ${\mathrm{Ge}}_{0.5}$ and Si varies strongly as a function of laser wavelength.