Single quantum dots as local probes of electronic properties of semiconductors

We investigated size- and excitation-intensity-dependent changes of the luminescence spectra of single In0.14Ga0.86As/GaAs quantum dots with diameters between 200 and 40 nm. The dot sizes investigated range from effectively two-dimensional structures down to diameters which are comparable to the length scales of electronic excitations, e.g., the excitonic Bohr radius, or of compositional fluctuations at interfaces. For dots occupied by single excitons, the luminescence linewidth decreases continuously with decreasing diameter. Using model calculations we relate this behavior to compositional fluctuations and obtain an estimate for their characteristic length scale. If the dots are occupied by several excitons the luminescence linewidth increases systematically with decreasing size. We describe this behavior by a model of carrier-carrier interaction effects on the luminescence linewidths.