The optical and vibrational properties of the quaternary chalcopyrite semiconductor alloy AgxCu1-xGaS2

The absorption, emission and Raman spectra of the quaternary chalcopyrite alloys AgxCu1-xGaS2 have been measured as a function of the Ag concentration. We find strong and highly nonlinear dependence on the alloy concentration in the optical band gap (a large bowing parameter). On the other hand, most of the Raman peaks exhibit either small energy shifts or large broadening with alloying. We conclude that the effect of substitution of the Ag cations by Cu in AgGaS2 on its band structure cannot be predicted by the simple virtual crystal potential approximation as a result of the large difference in electronegativity and bond length between Ag and Cu. (C) 2000 American Institute of Physics. [S0021-8979(00)00308-X].