Optical properties ofGa0.8In0.2As/GaAs surface quantum wells

We have investigated the photoluminescence of ${\mathrm{Ga}}_{0.8}$ ${\mathrm{In}}_{0.2}$As quantum wells where the top barrier is defined by the surface of ${\mathrm{Ga}}_{0.8}$ ${\mathrm{In}}_{0.2}$As layers. The spectra of surface quantum wells are compared to the emission of GaAs/${\mathrm{Ga}}_{0.8}$ ${\mathrm{In}}_{0.2}$As/GaAs quantum wells with varying GaAs top barrier thicknesses. Due to the increase of the confinement potential in the surface quantum wells we observe a significant blueshift of the emission line (of about 20 meV) compared to the emission line of quantum wells with a thick semiconductor barrier. The experimentally observed energy shift and line broadening for surface quantum wells as well as the onset of the blueshift for quantum wells with thin top barrier layers can be modeled by assuming a 5-eV electron affinity. For quantum wells with top barrier thicknesses below 10 nm we observe a decrease of the emission intensity due to nonradiative recombination at the surface.