Room-temperature emission of highly excited GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum wells

The emission spectra of GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum wells were studied under high optical excitation at room temperature. Mesa structures of 50 μm in size were used to confine the electron-hole carrier system laterally and thus to produce a uniform high density of carriers. Carrier densities were sufficient to fill the quantum well to the top of the ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As barrier, and electron subbands up to n=3 were filled. Accurate values of the densities and temperatures were obtained by fitting the spectra using calculations of the full coupled valence bands for the hole dispersion relations and for the optical matrix elements. The resulting band-gap renormalizations were found to depend on the subband index. Theoretical results based on an extension of the local-density approach are presented which are consistent with the observed subband dependence of the band-gap renormalization.