Contribution of E1-, E'0-, E2- and E'1-type transitions to the optical spectra of AgGaS2and AgGaSe2chalcopyrite compounds

Abstract

In previous papers published on the optical spectra of the AgGaS2 and AgGaSe2 chalcopyrite semiconductors, no explanation has been given as to the origin of most of the structures and the assignments proposed for some of them do not agree with the position of the Ag(d) levels in chalcopyrite compounds determined by photo-emission nor with the weakness that pseudo-direct transitions should present. The authors report the results of room temperature reflectivity measurements performed on AgGaS2 and AgGaSe2 for energies ranging from 1.2 to 25 eV, and propose that, in spite of the presence of d levels of Ag inside the valence band, the reflectivity spectra are essentially dominated by the existence of transitions of E1, E0, E2 and E'1 type (as in II-VI compounds), with an additional contribution of AG(d) levels and the possible occurrence of pseudo-direct transitions.