Electronic coupling and thermal relaxation in self-assembled InAs quantum dot superlattices

We report optical and structural characterizations of InAs quantum dot superlattices grown by molecular beam epitaxy on GaAs (001). Cross-sectional electron microscopy imaging reveals similar to 20 nm diameter InAs islands well aligned along the growth direction. Low temperature photoluminescence spectra exhibit a clear redshift with decreasing island vertical separation, as a result of electronic coupling between stacked dots, given that the larger shift is obtained for 70 A spacing. At high excitation power, the photoluminescence spectra show a doublet structure corresponding to coupled and uncoupled quantum dot states. The temperature dependence of the photoluminescence indicates that thermionic emission activation energy is much lower than the estimated barrier height. Such a difference is explained by the presence of non-radiative recombination centers due to strain relaxation and In segregation.