Laser-frequency dependence of Raman modes in GaAs-AlAs superlattices

The excitation frequency dependence of the Raman spectra in short-period GaAs-AlAs superlattices is studied. The off-resonance Raman spectra can be explained by a disorder-induced breakdown of wave-vector conservation leading to the contribution of small magnitude, random orientation wave-vector phonons. As extreme resonance is approached, double-resonance effects cause phonons with large magnitude, preferentially in-plane wave-vectors to dominate the Raman spectrum.