Annealing behaviour of photoluminescence spectra on Cu2ZnSnS4 single crystals.

We have measured photoluminescence (PL) spectra at 10 K for Cu₂ZnSnS₄ (CZTS) single crystals grown by the iodine transport method and explored the anneal changes of PL spectra under a Zn and S-saturation. All the crystals showed S- and Zn-poor composition, and nearly stoichiometric composition of Cu/(Zn + Sn). The observed PL spectra are divided into two groups; one is PL band with a peak at ∼1.3 eV (1.3-eV band), and another is PL band with a peak at ∼1.35 eV (1.35-eV band). It was found from SEM observations that the 1.35-eV band was observed in crystals with a mirror-like facet and, on the other hand, the 1.3-eV band was seen in the crystals with some small dark areas where the composition is Cu-poor. The Zn-saturated annealing at 600 °C caused the PL peak shift of ∼0.1 eV, from 1.295 to 1.185 eV. The S-saturated annealing at 550 °C caused a disappearance of PL emission. The implications of these annealing behaviour are discussed. [ABSTRACT FROM AUTHOR]