The effects of excess electron occupation on the optical properties of excitons ͑X͒ and biexcitons (2X) in a single self-assembled InGaAs quantum dot are investigated. The behavior of X and 2X differ strongly as the number of excess electrons is varied with the biexciton being much more weakly perturbed as a result of its filled s-shell ground state, a direct manifestation of shell-filling effects. Good correlation is found between charging thresholds observed from s-shell recombination perturbed by p-shell occupation, and direct observation of p-shell recombination.

Charged (X*) and neutral ͑X͒ exciton recombination is reported in the photoluminescence spectra of single In͑Ga͒As quantum dots. Photoluminescence excitation ͑PLE͒ spectra show that the charged excitons are created only for excitation in the barrier or cladding layers of the structure, consistent with their charged character, whereas the neutral excitons in addition show well-defined excitation features for resonant excitation of the dots. The PLE spectra for X and X* exhibit a clear anticorrelation in the region of the wetting layer transition, showing that they compete for photocreated carriers.

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We report a study of the gain characteristics of a self-organized InAs/GaAs quantum-dot laser. Using the Hakki–Paoli technique, we are able to determine the spectral form of the modal gain, its dependence upon current, and the differential gain. A quasiperiodic modulation of the below-threshold gain is observed. This modulation is shown to be responsible for the form of the lasing spectra, which consist of groups of lasing modes separated by nonlasing spectral regions. Possible mechanisms for this behavior are discussed.

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