Exciton Complexes in Self-Assembled In(Ga)As/GaAs Quantum Dots

Abstract

In this contribution we will present the results of our recent spectroscopic studies of single In(Ga)As/GaAs self-assembled quantum dots. We will develop the relation between the excitonic states in quantum dots and the confined single particle shell structure, for which we have studied the absorption spectrum of excitons by photoluminenscence excitation spectroscopy. We find that the absorption varies strongly with the symmetry of the dot structures: It becomes increasingly complicated the more the symmetry of the quantum dot is reduced. For dots of high symmetry we demonstrate that a non-trivial mixing of quantum configurations of the interacting electron--hole complex leads to distinct absorption spectra which are controlled by the number of confined electronic shells. We will also discuss the impact of exciton--phonon interaction on the optical spectra. Most importantly, for temperatures \(T \to 0\)the width of the emission lines seems to be limited by the radiative lifetime of the excitons only. However, already at moderate temperatures the coupling to phonons has a considerable influence. In particular, at room temperature the linewidth is on the order of several meV, so that the term ‘artificial atom’ is no longer justified. Then we will turn to fine structure effects of excitons confined in quantum dots. We will demonstrate that the fine structure is a very sensitive tool to obtain insight into the symmetry of the quantum dots. An intentional symmetry breaking can be induced by a magnetic field with an orientation different from the quantum dot symmetry axis. This allows for a detailed study of dark excitons. Further, we show how charged excitons can be distinguished from neutral excitons by looking at the fine structure. Finally, we will discuss the simplest functional unit that can be assembled from quantum dots, the ‘two-atomic’ quantum dot molecule. We will demonstrate a tunneling induced splitting of the energy levels which can be as large as 30 meV for barrier widths below 5 nm. Looking for these systems at the exciton fine structure gives a unique proof of the coherent coupling of the electronic states of the two quantum dots.KeywordsMesa StructureZeeman InteractionGround State ExcitonHomogeneous LinewidthExciton Wave FunctionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.