The experimentally observed energy band gap difference (Delta E-1) between
the I-III3-VI5 and I-III-VI2 and the energy band gap difference (Delta E-2)
between the I-III5-VI8 and I-III-VI2 phases of Cu-In-Se, Cu-Ga-Se, Cu-In-T
e, and Cu-Ga-Te systems is explained in terms of the relative shift of the
conduction band minimum (CBM) and the valence band maximum (VBM) caused due
to the presence of the ordered V-Cu and [In(Ga)(Cu)(+2)+2 V-Cu(-1)] defect
pair and to the effect of the p-d hybridization. The nearly linear variati
on of Delta E-1 and Delta E-2 with p-d hybridization of the corresponding I
-III-VI2 phase suggests that in selenides the lowering of the VBM predomina
tes over that of the CBM. In the case of the Cu-In-Te system, they are very
near the same magnitude, whereas in Cu-Ga-Te the lowering of the CBM predo
minates over that of the VBM. (C) 2000 American Institute of Physics. [S000
3-6951(00)01927-6].