Photoluminescence study of self-assembly of heterojunction quantum dots(HeQuaDs)

Recently quantum dots (QDs) have been the topic of extensive research. Unique properties arise in QDs due to a combination of the localized nature of their wavefunctions and a singularity in the associated density of states. Many strained III-V semiconductor film-substrate systems form QDs via a self-assembly process by means of a Stranski-Krastanov process. The strain relief responsible for the 3D nucleation causes a variation in the in-plane lattice constant which allows subsequent QD layers separated by thin spacer layers to be vertically stacked. Recently this concept has been extended to allow the formation of a heterojunction quantum dot (HeQuaD). In this structure an initial self-assembled QD (SAQD) is formed and then a different similarly strained material is nucleated on the initial SAQDs forming a crown on the underlying QD. This crown is also of a size appropriate to cause quantum confinement. In particular a stack of 4 layers of a HeQuaD structure of a GaSb crowned InAs SAQD on GaAs with GaAs spacer layers has been formed. The top HeQuaDs have been left uncapped to allow AFM analysis of the morphology. Photoluminescence of the HeQuaD has 3 peaks at similar to 0.95eV, 1.15eV, and 1.35eV. We have measured the intensity and temperature dependence of these PL peaks.