Photoluminescence characterization of interlayer carrier injection from InGaAs quantum well to InGaAs surface quantum dots with respect to GaAs spacer thickness

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.