Effect of an electric field on electronic excitations in double quantum wells

We have measured photoluminescence (PL) and inelastic light scattering spectra of GaAs/AlGaAs double quantum wells (DQW). The structures contain a high-mobility two-dimensional (2D) electron gas produced by modulation doping. The electron density as well as the intersubband spacings of the DQWs are changed by applying a DC voltage between a top and a bottom contact. Band-gap renormalization effects are observed in PL spectra when an excited subband becomes populated with electrons, as the 2D density increases. Inelastic light scattering yields information on the bias dependence of collective intersubband excitations of the 2D electron gas. The applied voltage reduces the coupling between layers leading to an energy shift of the excitations in each well in different directions.