Raman scattering by LO phonons in (GaAs)n1/(AlAs)n2 ultrathin-layer superlattices.

Abstract

Raman spectra of (GaAs${)}_{\mathit{n}1}$/(AlAs${)}_{\mathit{n}2}$ ultrathin-layer superlattices were measured at room temperature and under off-resonance conditions. The experimental results show that there are two effects in ultrathin-layer superlattices: the confinement effect of LO phonons and the alloy effect. It is found that the relative intensity of the disorder-activated TO mode can give a measure of the alloy effect. The Raman spectra of one-monolayer superlattices measured in various scattering configurations are very similar to those of the ${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$As alloy, and thus the alloy effect is prominent. However, in the case of monolayer number n\ensuremath{\ge}4, the confined effect is prominent, while the alloy effect is only shown as an interface effect.