On the prospect of identifying visible emissions from optical measurements of self-assembled QDs

The work presented here focuses on the optical properties of molecular beam epitaxy-grown self-organized InAs quantum dots (QDs). Under low excitation power densities, the photoluminescence (PL) spectrum of the structure under study exhibits a double-peak profile, which has been related to the optical emission from the dots. To properly argue for or against explaining a high energy peak as being the result of different-sized QDs or excited state emissions, a comparative study of the optical properties of a set of two grown QD samples was employed. The laser power dependence of the linearity of the PL intensities of the QD transitions was shown to be very useful in determining the possible origins of the PL sub-bands detectable in a double-peak emission from an ensemble of self-organized QDs. Indeed, the change in the linearity of the dot-luminescence intensity with the increase of the excitation density could give helpful information about the active confinement states from which the dots are emitting. On the other hand, despite the use of very low excitation power densities, the optical measurements of the studied structure have revealed an appearance of a PL signal relating to the radiative emission from the first excited state of the dots. A random pathway of carrier capture by the intrinsic levels of the QDs is thought to be the most likely cause of this aspect.