Engineering the bandgap of ferroelectric ZnSnO$_3$ via sulfur substitution

Since its recent discovery, ferroelectric ZnSnO$_3$ has been investigated for utility in a number of applications. Its strong remnant polarization and good conductivity, for example, make it attractive as a photovoltaic material, but its relatively large 3 eV bandgap limits its potential usefulness. We find that the bandgap of ZnSnO$_3$ is highly sensitive to changes in lattice volume, which can be effected either with application of external strain or by substituting sulfur for oxygen. Upon forming the fully-substituted ZnSnS$_3$, the bandgap reduces to a near-optimal 1.3 eV while retaining many of the important properties of the oxide, including a strong polarization. In this talk we describe the physics governing the tunable electronic structure of ZnSnO$_3$, discuss the stability of the ZnSnS$_3$ analogue, and propose a route to its use in a photovoltaic cell by growth on a GaN substrate.