Optical Properties of III–V Quantum Dots

Abstract

Results on excitonic properties of few and many particles-complexes confined in self-organized In(Ga)As/GaAs and InGaN/GaN quantum dots (QDs) are highlighted. The renormalization of transition energies in InGaAs QDs is found to be proportional to the number of excitons per dot and in the wetting layer. Resonant Raman scattering on such dots reveals localized TO- and LO-like phonon modes being blue shifted with respect to unstrained InAs bulk modes, and a localized interface mode. The localized modes are largely independent on the structural properties of QDs within different samples. Embedding InAs QDs in an InGaAs well shifts the QDs’ emission to lower energies. The reduction of strain is identified as the main reason for this redshift. Binary InAs/GaAs dot ensembles show a distinct formation of subensembles due to self-similar shapes and height variations in steps of integral InAs monolayers. A decreasing number of excited states with decreasing QD size is observed. Spectra of individual dots in such ensembles reveal a biexciton binding energy changing from binding to antibinding as the size of the dots decreases. The trend is well explained by a varying number of bound hole states. Furthermore, a monotonous decrease of the exciton fine-structure splitting with QD size from large values of 0.5 meV to small and even negative values is found, highlighting the effect of piezoelectricity. For nitride structures a clear proof of the quantum-dot nature is provided by resonantly excited time-resolved photoluminescence. Single InGaN QD emission-lines show a pronounced linear polarization, which is attributed to the valence band structure of the wurtzite type nitrides.