Abstract:Surface photovoltage (SPV) and photoluminescence excitation (PLE) spectroscopy have been used to characterize multiple stacked self-assembled InAs quantum dot (QD) structures with and without InGaAs overgrown layers. The SPV spectra contain rich optical features that originate from every relevant portion of the samples, including the QDs, wetting layer (WL), hybrid quantum well (HQW), and GaAs barrier. The excited state peak positions detected by PLE coincide with those from SPV measurements, which indicates that the QD ensembles are of monomodal distribution. The redshifts of the QD transitions have been attributed to the altered strain distribution, and the reduction in the linewidth of the WL signals indicates a partial alleviation of the surface roughness effect by the incorporation of InGaAs overgrown layers. An additional spectral feature situated between the highest lying QD state and the WL signals has been attributed to the electronic transition in the InAs/InGaAs dots-in-well structure.