ELECTRON COUPLING EFFECTS ON NEGATIVELY CHARGED EXCITONS IN GAAS DOUBLE-QUANTUM WELLS

We study inter-well coupling effects on the photoluminescence (PL) spe ctra of remotely doped GaAs double quantum wells (QWs). The resonance of the electron and exciton energies is tuned by biasing front and bac k gates on the structure, thereby controlling the electron density in either QW. By choosing the two wells to have different widths we can r esolve their PL spectrally. The indirect recombination involving elect rons 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 delocalis ed state of the negatively charged exciton (X-) consisting of a hole a nd an electron in either QW. We show that, unlike for the neutral exci ton, the X- transition, X--->e(-) + photon, is sensitive to net only i nter-QW coupling of excitons, but also to that in the excess electron (e(-)) states. The latter gives a direct measure of the interaction en ergy of the single particle electron subbands of the two wells. Away f rom the resonance condition where there are nearly equal electron dens ities in the two wells, the excitonic spectrum is remarkably insensiti ve to the presence of a dense electron gas in the other well. This ind icates that the excitonic interaction is destroyed by state exclusion in a dense electron gas, rather than screening and also that localisat ion by remote donor ions has little influence on X-. (C) 1998 Elsevier Science Ltd. All rights reserved.