SINGLE QUANTUM DOTS AS LOCAL PROBES OF ELECTRONIC-PROPERTIES OF SEMICONDUCTORS

We investigated size- and excitation-intensity-dependent changes of th e luminescence spectra of single In0.14Ga0.86As/GaAs quantum dots with diameters between 200 and 40 nm. The dot sizes investigated range fro m effectively two-dimensional structures down to diameters which are c omparable to the length scales of electronic excitations, e.g., the ex citonic Bohr radius, or of compositional fluctuations at interfaces. F or dots occupied by single excitons, the luminescence linewidth decrea ses continuously with decreasing diameter. Using model calculations we relate this behavior to compositional fluctuations and obtain an esti mate for their characteristic length scale. If the dots are occupied b y 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.