Triply resonant Raman scattering via nonequilibrium phonons in GaAs quantum wells

We present results on a low-frequency Raman mode in single GaAs quantum wells whose valence subband spacings match confined-optical-phonon energies. The excitation at about 3 meV has been previously interpreted in terms of an interband difference scattering of confined TO and LO phonons. The resonance profile of the Raman peak and uniaxial-stress dependence of the excitation spectra confirm the extreme triple resonance and the difference phonon scattering process. The dependence of the Raman activity on the incident laser power is consistent with the mediation by nonequilibrium phonons that is necessary to yield this unusual excitation.