Free-carrier screening of the interaction between excitons and longitudinal-optical phonons in ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As-InP quantum wells

The strength of the exciton–longitudinal-optical- (LO) phonon (Fröhlich) interaction as a function of sheet carrier density ($n_s$) is studied in Schottky-gated, modulation-doped ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As-InP quantum wells. LO-phonon satellites of the heavy-hole exciton photoluminescence line, enhanced by hole-localization effects, are observed at low carrier density. The satellites become very weak for $n_s$ greater than ∼3×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$, as a result of screening of the Fröhlich interaction with increasing carrier density. Clear evidence for hole localization at high $n_s$ is obtained from magnetic field measurements.