Si-doping and annealing effects on In 0.5Ga 0.5As/GaAs quantum dots grown by heterogeneous droplet epitaxy

We investigated the Si-doped In_0.5Ga_0.5As quantum dots (QDs) grown by heterogeneous droplet epitaxy method and the annealing effects on the optical properties through photoluminescence (PL) spectroscopy. All together two or three peaks related to the QDs appear on the PL-spectra for undoped and lightly doped samples at low temperature. But, heavily doped sample, the free electron concentration is so high that it can screen the Coulomb interaction between electron and hole. Therefore, it is very difficult to form excitons. After, post-growth annealing, thermal intermixing was found to result in significant blue-shifts of the PL emission at annealing temperatures up to 800°C and a decrease of the intersublevel energy spacing (ΔE) as much as 22.7 meV. In addition, the inhomogeneously broad line width of PL spectra become narrow with increasing annealing temperature. These results have been explained by the interdiffusion of In-Ga atoms at the interface between the QD and the GaAs barrier, which changes the composition of the QDs.