Optical charaterization of Ag/Ga composition ratio in AgGaSe2 thin film

AgGaSe2 thin films, changing the Ag/Ga ratio from 0.4 to 1.5, on glass substrates were successfully grown by vacuum evaporation method. Fundamental absorption bandedges were clearly observed except for Ag/Ga ratios of 0.4 and 1.5 in the optical transmittance spectra at RT. The optical bandgap increased with increasing Ag/Ga ratio. This was due to the Bernstein-Moss shifts. Photoluminescence spectrum was strongly observed in the stoichiometric sample in comparison to Ag- and Ga-rich samples. This means that nonradiative recombination transition was a few in the stoichiometric sample because there were few defects in the samples Two distinct peaks at 1.77 and 1.70 eV were clearly observed in the stoichiometric sample. They were due to bound exciton emission and donor-acceptor pair (DAP) emission, respectively. The DAP emission is due to recombination between Se- and Ga vacancies. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)