In-plane quantum-dot superlattices of InAs on GaAsSb/GaAs(001) for intermediate band solar-cells

Semiconductor quantum-dot superlattices (QD-SLs) have attracted considerable interests for intermediate band solar-cell (IB-SC) applications. In this study, in order to develop the IB-SCs using in-plane QD-SLs, ultra-high density InAs QDs with 4.0×10¹¹ cm^-2 were grown on the GaAsSb/GaAs(001) by molecular beam epitaxy. The average lateral size and height of the InAs QDs were 17 nm and 2.8 nm, respectively. In spite of the closely-packed QD structure, the coalescence of neighbouring QDs was effectively suppressed by the Sb surfactant effect. The in-plane QD-SL characteristics based on the minibands were confirmed by photoluminescence (PL) properties. The InAs QD-SLs were capped by the GaAsSb layers to construct a type-2 band alignment. From time-resolved PL measurements, long carrier lifetime of 6.9 ns was obtained for the in-plane InAs QDs with the GaAsSb capping layer. Internal quantum efficiency (IQE) of the IB-SCs using the in-plane InAs/GaAsSb QD-SLs was evaluated, and the extended IQE was observed from 900 nm to 1300 nm. It was attributed to the optical absorption at the GaAsSb layers and the InAs QDs. The IB-SCs including three stacked in-plane QD-SLs enhanced the extended IQE.