Near-field spectroscopy of a gated electron gas: a direct evidence for   electrons localization
  The near-field photoluminescence of a gated two-dimensional electron gas is measured. We use the negatively charged exciton, formed by binding of an electron to a photo-excited electron-hole pair, as an indicator for the local presence of charge. Large spatial fluctuations in the luminescence intensity of the negatively charged exciton are observed. These fluctuations are shown to be due to electrons localized in the random potential of the remote ionized donors. We use these fluctuations to image the electrons and donors distribution in the plane. 
G. Eytan, Y. Yayon, M. Rappaport, H. Shtrikman and I. Bar-Joseph