Band structure engineering of type-II GaSb/GaAs quantum rings for intermediate band solar cells

Abstract

Type-II quantum-confined heterostructures constitute a promising approach to realise highly efficient intermediate band solar cells (IBSCs), due to their long radiative lifetimes and the flexibility with which their electronic and optical properties can be engineered. To quantify the potential of type-II GaSb/GaAs quantum rings (QRs) for IBSC applications we undertake a theoretical investigation of their electronic properties. In these heterostructures the intermediate band is formed by bound hole states which are strongly localised within the QR. We demonstrate that the unconventional QR geometry provides a flexible platform to engineer the valence band structure, enabling optimum energy gaps – which maximise overall IBSC efficiency – to be obtained via structural optimisation. Our results emphasise that utilising QRs for IBSC applications requires careful control of QR morphology in epitaxial growth.