PHOTOEMISSION OF AG, CU, AND GE-DOPED ALPHA-GA2S3 CRYSTALS

Photoluminescence of alpha-Ga2S3 crystals doped with the Ib elements (Ag, Cu) and the IVb element (Ge) has been observed. The dominant emission band corresponding to the 2.38 eV green-band in the undoped crystals appears at 2.50 eV in the Ag-doped crystals and 2.41 eV in the Cu-doped crystals. In the Ge-doped crystals, the dominant emission band is situated at 2.10 eV. Applying the Prener-Williams model, it is concluded that the Ib element(Ag or Cu) in Ga2S3, like the Ga-vacancy, can be an activator having the nature of acceptor and causes the donor-acceptor pair emission associated with an iodine shallow donor of coactivator which is imbeded for the iodine-transport crystal growth. On the other hand, Ge can be considered to be a donor at 0.28 eV below the conduction band. Additional measurements of thermoluminescence, infrared absorption and optical absorption near the band gap support the above conclusion.