This work exploits carrier injection hybrid structures in which carriers are injected into a layer of In0.4Ga0.6As surface quantum dots (SQDs) from an adjacent In0.15Ga0.85As quantum well (QW) as a function of spacer thickness from 10 nm down to 2.5 nm. Photoluminescence (PL) measurements verify that all such hybrid structures indeed have carriers collected into the QW and subsequently obtain an enhancement for PL intensity over that of the reference SQDs. The hybrid structure with the 2.5 nm spacer obtains the best carrier injection efficiency, due to the strongest coupling between the QW and the SQDs, while a thicker spacer results in less carrier injection from decreased quantum tunneling. However, the carrier injection is less efficient than expected. This is due to the fact that the QW confined energy states line up with the broad wetting layer (WL) energy states of SQDs of our test samples, leading to resonant carrier tunneling from the QW to the WL. Thus, there is significant carrier loss through tunneling into the WL of SQDs and then to surface states via nonradiative recombination. This characteristic must be considered in the design of surface sensitive detection devices using SQD injection structures.

Exciton dynamics in a GaAsSb/GaAs quantum well (QW) heterostructure were investigated via both steady state and transient photoluminescence. The measurements at 10 K demonstrated the coexistence of localized excitons (LEs) and free excitons (FEs), while a blue-shift resulting from increased excitation intensity indicated their spatially indirect transition (IT) characteristics due to the type-II band alignment. With increasing temperature from 10 K, the LEs and FEs redistribute, with the LEs becoming less intense at relatively higher temperature. With increasing temperature to above 80 K, electrons in GaAs are able to overcome the small band offset to enter inside GaAsSb and recombine with holes; thus, a spatially direct transition (DT) appeared. Hence, we are able to reveal complex carrier recombination dynamics for the GaAsSb/GaAs QW heterostructure, in which the "S" shape behavior is generated not only by the carrier localization but also by the transformation from IT to DT with elevated temperature.