CdSe band-splitting on thermal annealed films

Abstract Semiconducting polycrystalline CdSe thin films were prepared on glass substrates by chemical bath at 65 °C. As-deposited films grew in the metastable cubic sphalerite (S) crystalline structure with good stoichiometry. Upon thermal annealing (TA) in Ar+Se2 atmosphere at different temperatures in the range 200–500 °C, the gradual phase transformation from cubic modification to hexagonal wurtzite (W) stable phase could be observed. From optical absorption measurements the fundamental energy band gap (Eg) and the second electronic transition (Eg+ΔEg) were calculated for as-deposited and thermal annealed films. For TA ⩽350 ° C , S-phase dominates the crystalline structure and only the spin orbit (ΔEso) contribution to ΔEg is present. Above 350 °C, the W-phase dominates and the energy splitting (ΔEcf), owed to crystal field contribution and originated by the loss of lattice symmetry, should be added to ΔEso in order to complete ΔEg in the W-phase. The values ΔE so =0.389±0.011 eV and ΔE cf =0.048±0.018 eV were found from our analysis, and T c =350 ° C was here defined as the critical point of the phase transformation.