Volume dependence of excitonic fine structure splitting in geometrically similar quantum dots

We investigate the fine structure splitting (FSS) of excitons confined in strain-free, highly symmetric GaAs/AlGaAs quantum dots (QDs) as a function of size. QDs with similar geometry are created by filling nanoholes on an AlGaAs surface with different amounts of GaAs. In turn, nanoholes of regular reversed-cone shape are obtained by Al-droplet etching of an AlGaAs layer. The resulting QDs have high optical quality, as witnessed by emission linewidths smaller than 20 mu eV under nonresonant excitation. The average FSS decreases from 12.5 +/- 6.4 to 3.6 +/- 1.7 mu eV as the QD height increases from 5.4 +/- 0.3 to 8.0 +/- 0.2 nm, following the expected 1/volume dependence. Theoretical calculations using atomic force microscopy data of QD structures as input show that the geometrical similarity of QDs is reflected in invariant aspect ratio and lateral elongation of the wave functions and reproduce the experimental FSS energies.