Effect of capping procedure on quantum dot morphology: Implications on optical properties and efficiency of InAs/GaAs quantum dot solar cells

InAs/GaAs quantum dot solar cell structures have been grown by metal organic vapor phase epitaxy, using partial capping of the quantum dots plus a subsequent thermal anneal. The optical characteristics of the InAs quantum dot layers have been studied as a function of the GaAs capping layer thickness and annealing temperature. We observe that a thinner capping layer and a higher annealing temperature result in lower non-radiative defect density and in improved quantum dot size homogeneity, leading to intense and sharp photoluminescence emission at low temperatures. We use an effective mass approximation model to correlate the photoluminescence emission characteristics to the quantum dot composition and dimensions. The resulting InAs/GaAs intermediate band solar cells show the best performance for the case of a 3 nm thick capping layer and annealing at 700 °C.