Refractive-index behavior of ternary chalcopyrite semiconductors

Refractive-index dispersion data for 11 I-III-VI2 and II-IV-V2 chalcopyrite semiconductors are analyzed with a view towards obtaining a good representation of the data, values of physically meaningful parameters, and estimates of errors. Using a moment decomposition analysis, it is found that (i) only four parameters (three electronic and one lattice) are required to fit each dispersion curve, (ii) all differences between chalocopyrites and their zinc-blende binary analogs can be viewed as simple band-gap-shift effects, (iii) in contrast to cuprous halides, oscillator strength contributions from d-electron valence states in Cu and Ag chalcopyrites appear to be negligible, (iv) energy downshifts in chalcopyrites involve the entire ε2 spectrum, and (v) there is no clear quantitative correlation between structural distortions in chalcopyrites and anisotropies in optical parameters related to the birefringence. Finally, a brief discussion of the applicability of model ε2 spectra to descriptions of refractive-index dispersion and related optical effects is presented.