Raman scattering near the (${\mathit{E}}_0$+${\mathrm{\Delta }}_0$) resonance from [211]-oriented ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{In}}_{\mathit{x}}$As/GaAs multiple quantum wells

We present a Raman-scattering study of [211]-oriented ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{In}}_{\mathit{x}}$As/GaAs multiple quantum wells grown by use of molecular-beam epitaxy. Off resonance, the Raman scattering satisfied bulk zinc-blende-structure selection rules. Near the (${\mathit{E}}_0$+${\mathrm{\Delta }}_0$) resonance, there is strong LO-phonon Raman scattering in the Z’(X’,X’)Z¯ ’ configuration, where Z’ refers to the growth axis and X’ is in a (1¯11) direction. LO-phonon Raman scattering is forbidden in this configuration by bulk zinc-blende-structure selection rules and does not occur (or at least is much weaker) in [211]-oriented GaAs substrates near this resonance. This Raman process is due to Fröhlich-interaction electron-phonon scattering activated by the strain-generated electric fields that occur in the multiple-quantum-well structure. We measure the resonance profile of this Raman process. The scattering efficiency is found to decrease with increasing laser intensity, because of a screening of the strain-generated fields by photoexcited free carriers. We present an electronic-structure calculation that accounts for the energy position of the resonance profile. Based on the electronic-structure results, we discuss simple models for the shape of the resonance profile. A free-carrier screening calculation accurately describes the observed laser-intensity dependence of the efficiency of this Raman process.