Temperature dependence of the band edge emission of the wide gap semiconductor (LaO)CuCh (Ch = S, Se, Te)

The layered oxysulfide (LaO)CuS is a transparent p type semiconductor with wide band gap of 3.2 eV, and shows an exciton emission at room temperature. In order to investigate its precise optical properties, we have synthesized a single phase of (LaO)CuCh (Ch = S, Se, Te) and measured the photoluminescence spectra at low temperature. The lattice constants of (LaO)CuCh increase in the order of the atomic number of the chalcogen atoms. All samples are p type semiconductors and the absolute value of the electrical conductivity also increases in the order of the atomic number of the chalcogen atoms. The sharp PL peak near the absorption edge of the reflectance, which originates from free and bound excitons, is observed at 4 Kin (LaO)CuCh. In addition, the exciton emission is observed in all samples at 300 K. The energy gap estimated from the diffuse reflectance varies from 3.2 eV for (LaO)CuS to 2.3 eV for (LaO)CuTe. These results are similar to the characteristics of typical II–VI semiconductors.