Epitaxial Lift-Off of Ultrathin Heterostructures for Hot-Carrier Solar Cell Applications

Abstract

Epitaxial lift-off, the separation of a device from its growth substrate through selective etching, is economically attractive for all III-V solar cells, enabling the reuse of the same substrate multiple times. It is even more interesting for ultrathin solar cells, where substrate removal is needed to implement light trapping. One promising example of ultrathin cells is the hot-carrier solar cell, a high-efficiency concept where the photo-generated electrons are at a higher temperature than the lattice. Our work focuses on these hot carriers, and the necessity for light trapping to develop high-efficiency hot-carrier solar cells. In this presentation, we report on the epitaxial lift-off of ultrathin GaAs-AlGaAs heterostructures. We bond these devices on gold, and separate them from their substrate using HCl to selectively etch an InAlP release layer. This method could be applied to all heterostructures that do not contain InP-based compounds. The photoluminescence spectrum is very similar before and after epitaxial lift-off, with a lower intensity we are working on improving. Our objective is to observe hot carriers in these devices. This would enable to study the influence of light trapping on hot carriers, and to implement these results into complete hot-carrier solar cells.