Near‐field light emission from dark‐states in semiconductor quantum dots

Abstract

AbstractWe theoretically study the carrier capture and distribution among the available energy levels of a symmetric semiconductor quantum dot under continuous‐wave excitation resonant with the barrier energy levels. We find that at low temperature all the dot level‐occupations but one, the second (dark) energy level,decrease monotonically with energy. The second energy level, displays a steady‐state carrier density exceeding that of the lowest level more than a factor two (see the figure). This nonequilibrium effect does not origin from radiative recombination before relaxation to lower energy levels, but at the opposite, it is consequence of carrier trapping due to the symmetry‐induced suppression of radiative recombination of the second (dark) energy level. While the observation of such effect by means of far‐field spectroscopy is prevented, scanning near‐field optical microscopy, able to detect the evanescent waves generated by dark‐states occupations, can be adopted to inspect such nonequilibrium effects at the nanoscale. Exciton‐level occupations of the dot (normalized at the maximum) calculated for two different temperatures. See Sect. 3 for a detailed description of the results here displayed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)