Resonance effects in first- and second-order Raman scattering from AlAs.

Abstract

First- and second-order Raman scattering has been studied in epitaxial AlAs grown by solid-source molecular-beam epitaxy. A strong resonant enhancement of dipole-forbidden one-LO and intrinsic two-LO-phonon scattering is observed for excitation at the band-gap energy ${\mathit{E}}_{0}$. Maxima in the second-order Raman spectrum for excitation both at and below the ${\mathit{E}}_{0}$ gap resonance are assigned to contributions from various critical points of the Brillouin zone. Published data of ab initio calculations of the AlAs phonon dispersions are found to be in good agreement with the measured frequency positions of the second-order Raman bands. In highly carbon-doped p-type AlAs layers the local vibrational mode of the carbon acceptor (${\mathrm{C}}_{\mathrm{As}}$) is observed at about 635 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.