Disorder-tunable ZnGeP2 for epitaxial top cells on Si

There has been a longstanding search for top cell materials for Si-based tandems. ZnGeP2 is one material that could fit this need. It is lattice matched to Si and has the potential for tuning its band gap at fixed lattice constant via cation ordering. In this study, we investigate the effects of growth and annealing conditions on the structure of ZnGeP2 thin films. Films were deposited amorphous and then annealed ex-situ. Using low anneal temperatures or short anneal times, we were able to kinetically trap the disordered phase. We also found composition to play a role in the degree of ordering in our films. Our findings support the hypothesis that ZnGeP2 could be implemented as a material with tunable properties at fixed lattice constant through cation ordering.