Identification of defect levels in Cu x Ag 1−x InSe 2 thin films via photoluminescence

Defect levels in polycrystalline thin films of Cu x Ag 1−x InSe 2 deposited with x=0, 0.6, and 1.0 have been studied via photoluminescence (PL) spectroscopy. Optical transitions were identified for the films. The type of defects involved and their position in the energy gap were determined from power- and temperature-dependent PL analysis. Donor-acceptor pair transitions were observed as well as transitions from either band tails or shallow hydrogenic states near the band edges. Significant subgap emission was observed between the near band edge and ∼750 meV photon energies in all samples. An optimum Ag content was identified between 0.2 < × < 0.6.