Effect of Ga incorporation on valence band splitting of OVC CuIn3Se5 thin films

Polycrystalline thin films of CuIn2.95Ga0.05Se5 produced by the incorporation of Ga into the ordered vacancy compound CuIn3Se5 by a two-stage vacuum evaporation process were structurally, compositionally and optically characterized using X-ray diffraction, energy dispersive analysis of X-rays and optical absorbance measurements. From the X-ray diffraction data of the films, the structural parameters like lattice constants, tetragonal deformation, bond lengths and anion displacement were evaluated and their effect on the optical behavior of films was discussed. The Hopfields quasi-cubic model adapted for chalcopyrites with tetragonal deformation was used to elucidate the crystal field and spin orbital splitting parameters in the uppermost valence band of the compound, using the three energy gaps 1.649, 1.718 and 1.92 eV corresponding to the threefold absorption in the fundamental absorption region of the optical spectra of these films. The percentage contributions of Se p and Cu d orbitals to p–d hybridization in this compound were calculated using linear hybridization of orbitals model and the effects of p–d hybridization on the band gaps were studied.

Graphical AbstractThe figure shows lifting of degeneracy in the upper valence band levels when there is only crystal field splitting in chalcopyrites and also when both crystal field splitting (ΔCF=−0.09 eV) and spin orbit splitting (Δso=0.226 eV) are present as in CuIn2.95Ga0.05Se5 films. A–C denote transitions between conduction band minimum and the valence band split levels, which gave rise to the three band gaps evaluated from the threefold absorption observed in the fundamental absorption region of the films.Figure optionsDownload as PowerPoint slideResearch highlights
► Initiating study on valence band splitting in Ga incorporated ordered vacancy compound CuIn3Se5.
► Correlation of splitting parameters and structural parameters of the compound.
► Variation in band gap of the compound due to p–d hybridization.