Resonant first- and second-order Raman scattering in AlSb.

Abstract

We have studied the resonant Raman scattering by one and two LO phonons in the vicinity of the ${\mathit{E}}_{0}$ gap of AlSb at 20, 100, and 300 K. The first-order allowed and forbidden scattering, as well as their interferences, are greatly enhanced by excitonic effects. A theory that takes into account excitons as virtual intermediate states has been used for the interpretation of the measured absolute scattering efficiencies. Good quantitative agreement is obtained for allowed and forbidden scattering and a reasonable qualitative agreement for their interferences. In the case of forbidden scattering, the efficiencies measured at high temperature are stronger than the low-temperature ones, a fact that can be explained if we assume an extrinsic impurity-induced Fr\"ohlich mechanism. Second-order scattering is compared with predictions based on uncorrelated electron-hole pairs. In order to reproduce the absolute values of the Raman-scattering efficiency the theoretical intensities must be multiplied by a factor of 6, while in the first-order spectrum a factor of a thousand is needed if uncorrelated electrons are assumed. This means that excitonic effects are less important in second-order resonant Raman scattering. This can be attributed to the fact that the incoming photons resonate mainly with the continuum.