Experimental investigation and modeling of the fine structure splitting of neutral excitons in strain-free GaAs/AlxGa1-xAs quantum dots

We measure, by photoluminescence spectroscopy, the fine structure splitting (FSS) of bright excitons confined in a large number of elongated and unstrained Al0.35Ga0.65As/GaAs/Al0.45Ga0.55As quantum dots (QDs) and quantum-well potential fluctuations (QWPFs). While the FSS values are comparable, the light polarization directions for well-oriented QDs and randomly oriented QWPFs on the same sample are substantially different. We compare the results with model calculations using as input scanning probe microscopy data of QD structures nominally identical to those investigated by photoluminescence. The model reproduces well the polarization orientation for all studied samples and also the magnitude of the FSS, at least for relatively tall dots. We discuss the results and elucidate the role of in-plane elongation on the FSS.