Carrier-induced shift and broadening of optical spectra in an ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs quantum well with a gate electrode

We have investigated the carrier-induced changes in the photoluminescence (PL) and excitation spectra (PLE) of an n-type ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs quantum-well structure at 10 K by controlling the electron concentration ($N_s$=0–${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$) via gate electric fields. By comparison with local-density-functional theory, the red shift of the PL peak and the blue shift of the PLE spectra could be ascribed to band-gap renormalization (∼18 meV at $N_s$=1×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$) and to band-filling effect. While appreciable portions of the PL and the PLE linewidths are attributed to thermal broadening, the presence of additional broadening is noted and discussed in terms of the localization of carriers, the Auger effect, and other mechanisms.