Ultranarrow Luminescence Lines from Single Quantum Dots

We report ultranarrow $(<0.15\mathrm{}\mathrm{meV})$ cathodoluminescence lines originating from single InAs quantum dots in a GaAs matrix for temperatures up to 50 K, directly proving their $\delta$-function-like density of electronic states. The quantum dots have been prepared by molecular beam epitaxy utilizing a strain-induced self-organizing mechanism. A narrow dot size distribution of width $12\pm 1\mathrm{nm}$ is imaged by plan-view transmission electron microscopy. Cathodoluminescence images directly visualize individual dot positions and recombination from a single dot. A dense dot array $(\sim {10}^{11}\mathrm{dots}/{\mathrm{cm}}^2)$ gives rise to a distinct absorption peak which almost coincides with the luminescence maximum.