Minimum thickness MgO buffer layers for YBa2Cu3O7−x/GaAs structures: Assessment using photoluminescence of multiple-quantum-well structures

A GaAs-AlGaAs multiple-quantum-well structure was used as a substrate for overgrowth by a MgO buffer layer and superconducting YBa2Cu3O7−X thin film. The multiple quantum well serves as an in-depth probe for possible damage incurred by the semiconductor substrate due to the relatively high temperature and active oxygen environment that characterizes the superconductor growth. The thickness of the MgO buffer layer was varied and correlated with both the superconducting properties of the overlying YBa2Cu3O7−X and the quality of the substrate as determined by photoluminescence measurements of the multiple quantum wells. Both high quality superconducting YBa2Cu3O7−X and excellent photoluminescence spectra of the substrate were obtained with a MgO thickness of 450 Å and quantum wells as close as 350 Å to the surface.