Neutral, charged excitons and biexcitons in strain-free and asymmetric GaAs quantum dots fabricated by local droplet etching

We present an experimental and theoretical study of the optical properties of asymmetric strain-free GaAs quantum dots (QDs) fabricated by filling of self-organized nanoholes (NHs) created by local droplet etching. The energy levels are calculated within the effective mass approximation using as input a model anisotropic QD shape with $C_{2v}$ symmetry based on atomic force microscopy (AFM) profiles of NHs. The influence of the QD height and shape anisotropy on the exciton emission energy and the s-$p_x$ and s-$p_y$ energy splittings is studied theoretically. The experimentally observed bound nature of excitonic states is well reproduced by our theoretical approach which includes direct Coulomb energies and correlation effects. We investigate the fine-structure splitting (FSS) of the neutral exciton as a function of dot size. Theoretical calculations of the long-range electron-hole (e-h) exchange interaction predict an increase of the FSS with decreasing QD height, which describes well the experimental trend.