Optical Properties and Electronic Structure of Copper Zinc Sulfide Nanocrystals

Continued efforts to transition toward renewable energy sources have spurred tremendous research into the discovery of near-infrared gap semiconductors. Here we describe the optical properties and electronic structure of copper zinc sulfide nanocrystals, with copper mole fractions as high as x(Cu) = 0.18. Copper zinc sulfide is shown to be a near-infrared gap semiconductor that exists in both zinc blende and wurtzite forms, similar to ZnS. The bandgap is shown to vary over 3.45-2.15 eV as the copper mole fraction is changed from 0.01 to 0.18. We find that the valence band of CuZnS nanocrystals has a significant tendency for hole localization, similar to other highly mismatched alloys. Further, our ultrafast studies are consistent with rapid (450 +/- 60 fs) removal of conduction band electrons and subsequent defect emission over 4.3 ns.