Excitons in Asymmetric Nanostructures: Confinement Regime

Quantum confinement of electrons and holes in semiconductor nanostructures results in quantization of their energy levels with level spacing generally decreasing with the confinement length. The relation between these splittings and the energy of the electron-hole Coulomb interaction may serve as a measure of exciton confinement regime. We consider theoretically strongly in-plane asymmetric nanostructures, like InAs/AlGaInAs elongated quantum dots. Based on optical properties, we find a possible indication of coexistence of different confinement regimes for the two bright exciton states that couple to light polarized along the two nonequivalent axes distinguished by the structural asymmetry. Exciton lifetimes and their distinct dependences on energy derived here for the two confinement regimes are in good agreement with those of recently measured double exponential photoluminescence decays. Additionally, for highly elongated dots, one of the states exhibits properties typical for the weak confinement regime, which may have a significant impact on spin relaxation processes.