Electron coupling effects on negatively charged excitons in GaAs double quantum wells

Abstract

We study inter-well coupling effects on the photoluminescence (PL) spectra of remotely doped GaAs double quantum wells (QWs). The resonance of the electron and exciton energies is tuned by biasing front and back gates on the structure, thereby controlling the electron density in either QW. By choosing the two wells to have different widths we can resolve their PL spectrally. The indirect recombination involving electrons and holes in different wells is observed to anti-cross the direct PL as a function of gate bias. There is also evidence for a delocalised state of the negatively charged exciton (X −) consisting of a hole and an electron in either QW. We show that, unlike for the neutral exciton, the X − transition, X −→e −+photon, is sensitive to not only inter-QW coupling of excitons, but also to that in the excess electron (e −) states. The latter gives a direct measure of the interaction energy of the single particle electron subbands of the two wells. Away from the resonance condition where there are nearly equal electron densities in the two wells, the excitonic spectrum is remarkably insensitive to the presence of a dense electron gas in the other well. This indicates that the excitonic interaction is destroyed by state exclusion in a dense electron gas, rather than screening and also that localisation by remote donor ions has little influence on X −.