Stranski-Krastanov InAs/GaAsSb quantum dots coupled with sub-monolayer quantum dot stacks as a promising absorber for intermediate band solar cells

The optical properties of the Stranski-Krastanov (S-K) grown InAs/GaAsSb quantum dots (QDs) coupled to sub-monolayer (SML) InAs QD stacks are investigated using photoluminescence (PL) spectroscopy. The PL emission peak of the S-K QDs shifts to shorter wavelengths with increasing the number of SML stacks (N_SML) due to the increasing strain fields from the SML QDs. The PL peak energy is linearly increased with increasing the cube root of excitation power, with a different ratio of the absorption coefficient to radiative recombination rate for all the QD samples. The total carrier lifetime for the S-K QDs is increased with increasing N_SML, most probably caused by the increase in the ground-state transition energy of the S-K QDs. The nonmonotonic behavior of the thermal activation energy of electrons in the S-K QDs is observed due to the N_SML-dependent variation of the strain and Coulombic interaction within the QDs.