Evolution from 2DEG to excitonic spectra in a modulation-doped GaAs/AlGaAs single quantum well

The magneto-photoluminescence (PL) and its excitation (PLE) spectra are studied in a single-sided modulation-doped GaAs/AlGaAs single quantum well. With lowering the two-dimensional electron gas (2DEG) density from n(2d) approximate to 1 x 10(11) to 1 x 10(10) cm(-2) by optical depletion, the 2DEG-free heavy-hole spectrum transforms into an exciton-like spectrum. Cyclotron resonance at microwave frequency is used in order to measure the 2DEG parameters in the entire range of n(2d). A narrow (0.6 to 0.8 meV) exciton-like PL line is observed when n(2d) is optically decreased to approximate to 1 x 10(10) cm(-2). This line shows a clear excitonic diamagnetic shift under a perpendicularly applied magnetic field (B = 0 to 4 T). Under these conditions the 2DEG microwave mobility is still high (approximate to 1 x 10(6) cm(2)/Vs). The lowest energy PL line does not show trion features, and by this it differs from other reported cases.