Macro-PL and SEM image. (a) Macro-PL (log scale) of low-density GaAs DE QDs with 22- and 45-nm cap at low temperature (12 K). The PL intensity was normalized with PL peak intensity of GaAs-related peak band around 830 nm. (b) SEM image (x300,000) of low-density GaAs DE QDs with 45-nm AlGaAs capping layer. The inset of Figure 3b is magnified by four for one QD.