Evolution from 2DEG to Excitonic Spectra in a Modulation-Doped GaAs/AlGaAs Single Quantum Well

Abstract

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 n2d ≈︂ 1×1011 to 1×1010 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 n2d. A narrow (0.6 to 0.8 meV) exciton-like PL line is observed when n2d is optically decreased to ≈︂1×1010 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 (≈︂1×106 cm2/Vs). The lowest energy PL line does not show trion features, and by this it differs from other reported cases.