Exciton binding energies in chalcopyrite semiconductors

The optical spectra of Cu-III-VI ₂ chalcopyrite compounds display rich excitonic features in the fundamental direct bandgap energy region. The energy structure of excited excitonic states reported in the literature are reexamined using a calculation of the eigenstates of the hydrogenic problem in the context of the anisotropic band structure and the anisotropy of the dielectric constant. We find some remarkable agreements as well as inconsistencies in the literature that we attribute to the following reasons: (i) the difficulty to interpret fine structure-splitting data in noncubic semiconductors, and (ii) the more severe difficulty growing these materials with high enough quality. We finally propose some values that match very well with recent proposals and integrate the trend between Rydberg energies and bandgap values for the binary inorganic zincblende and wurtzite semiconductors.