Excitonic emission in the presence of a two-dimensional electron gas: A microscopic view - art. no. 081308

摘要

The near- and far-field photoluminescence (PL) spectra of a gated two-dimensional electron gas have been measured in a GaAs quantum well. Scanning near-field measurements reveal the microscopic origin of the different line shapes of the neutral (X) and negatively charged (X-) exciton. We find a new broadening mechanism of the exciton: local density fluctuations give rise to spatial fluctuations of the local X peak energy, and hence to inhomogeneous broadening of the far-field X line. The X linewidth is therefore proportional to the width of the electron density distribution. On the other hand, we find that the X- is homogeneously broadened, and the numerator of its Lorentzian line shape is linearly proportional to the electron density. We present a simple method to determine low electron densities from the PL spectrum. [References: 19]