Density dependence of recombination rates in a gated GaAs/AlGaAs modulation doped quantum well

During the last years the physical properties of modulation doped quantum wells (MDQW) have attracted much attention from both a device as well as from a fundamental physics point of view. With these structures a degenerate one and more component Fermi system of reduced dimensionality can be realized, and e. g. many body effects can be investigated by means of optical spectroscopy /1-4/. In this paper we report on experimental studies of the carrier density dependence of the recombination dynamics. We have investigated a 13 nm wide n-type single MDQW by means of picosecond photoluminescence (PL) spectroscopy at low temperature (T = 4K). An external voltage perpendicular to the quantum well layer can be applied via a Schottky contact (evaporated on the surface of the sample) in order to vary the electron concentration in the quantum well between ns = 0 up to about 3 • 1011 cm-2 (details are reported in ref. /2,5,6/). Consequently, we can cover the regime where excitonic recombination takes place up to densities where the optical properties are governed by a one component free carrier plasma. We thereby have avoided the crucial disadvantage of comparing different samples, where the sample to sample variations of well width, interface quality, PL efficiency etc. complicate the physical interpretation.