TRIPLY RESONANT RAMAN-SCATTERING VIA NONEQUILIBRIUM PHONONS IN GAAS QUANTUM-WELLS

We present results on a low-frequency Raman mode in single GaAs quantu m wells whose valence subband spacings match confined-optical-phonon e nergies. 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 d ependence of the excitation spectra confirm the extreme triple resonan ce and the difference phonon scattering process. The dependence of the Raman activity on the incident laser power is consistent with the med iation by nonequilibrium phonons that is necessary to yield this unusu al excitation.