Enhanced Zn-Cd interdiffusion and biexciton formation in self-assembled CdZnSe quantum dots in thermally annealed small mesas

By controlled annealing of small ZnSe mesas with embedded CdZnSe quantum dots (QDs) at considerably low temperatures, significant changes of the QD luminescence have been observed. To investigate the spectral evolution of single exciton lines several thermal annealing steps were performed successively, and large energy shifts of single exciton (X) lines due to annealing were traced. In annealed QDs the biexciton (XX) emission is drastically enhanced. Biexciton binding energies less than 10 meV were recorded for the thermally annealed CdZnSe QDs, indicating a considerable change in the QD confinement. The pronounced energy shifts of the QD luminescence is attributed to the Cd-Zn interdiffusion between the CdZnSe QDs and the surrounding ZnSe matrix. In small mesas interdiffusion activation energy ( E A ) of less than 1 eV was determined. This value of E A is half of that recorded for the Cd-Zn interdiffusion in large QD ensembles, indicating that the sidewalls of the etched mesas play an important role in the observed diffusion process.