Optical Properties of InAs/AlAs Self-Assembled Quantum Dots

Abstract

The optical properties of self-assembled InAs quantum dots with AlAs barriers are reviewed. The dots are formed by self-organization of an InAs layer grown by molecular-beam epitaxy between layers of AlAs. The average size and density of the dots vary across the sample, to allow a systematic study as a function of quantum confinement. Single dot photoluminescence emission is observed at high energies (1.6-1.8 eV) compared to InAs/GaAs QDs. At even higher energies, a continuum emission is observed due to transitions involving electron extended states of the X conduction band of AlAs. The exciton and biexciton lines exhibit a fine-structure splitting due to anisotropic exchange energy, resulting in the emission of linearly counter-polarized doublets. The study of these doublets as a function of emission energy reveals a systematic dependence of electron interactions on dot size, in a similar way as in InAs/GaAs QDs. The biexciton binding energy and the fine structure splitting are essentially larger for AlAs barriers due to increased confinement. Photoluminescence excitation measurements reveal the spectrum of excited states of the QD. In some cases, clear photoluminescence excitation peaks evenly spaced at fixed energy intervals indicate a polaronic coupling inside the dots. From them, characteristic LO-phonon energy around 31 meV can be inferred for a single QD. Our results are discussed in the frame of the existing relevant knowledge of the optical properties and applications of semiconductor selfassembled quantum dots.