Photoluminescence study of InAs quantum dots with a bimodal size distribution

We have investigated photoluminescence (PL) spectra taken from a series of self-assembled InAs/GaAs quantum-dot (QD) heterostructures with different InAs coverages by performing excitation-power and temperature dependence measurements. The PL spectra exhibit a well-defined doublet-like QD peak with invariable energy positions regardless of the coverage attributed to a bimodal size distribution of small and large QDs. The power-dependent PL spectra show that the high-energy peak is composed of two contributions, one from the excited state of large QDs and the other from the ground state of small QDs, and the power dependence of high-energy peak becomes stronger with increasing the amount of InAs. This indicates that, in as-grown InAs QD ensembles grown under optimum growth conditions with appropriate InAs coverages, there can exist a specific bimodal size distribution consisting of large and small QD groups whose sizes are fixed, but whose numbers vary with the amount of InAs.