Strong enhancement of second-order response coefficients in tellurium containing Ag-III-VI2 compounds

First-principles calculations of the second-order optical response coeffici ents are reported for Ag-III-VI2 compounds with III=Ga, In and VI=S, Se, Te . While both the substitutions of In for Ga and Te for Se or S lower the ba nd gap by similar amounts, the substitution of Se by Te is significantly mo re favorable for increasing chi((2)). The enhancement of chi((2)) by a fact or 2 from AgGaSe2 to AgGaTe2 is surprising compared to the only modest enha ncement obtained in II-VI compounds. The origin of these enhancements is an alyzed in terms of the frequency-dependent response functions and the band structures. (C) 2000 American Institute of Physics. [S0003-6951(00)03728-1] .