Optical and structural properties of co-evaporated CuIn_(0.5)Al_(0.5)Se_2 thin films

摘要

CuIn_(0.5)Al_(0.5)Se_2 thin films are successfully prepared using a four-source co-evaporation technique on soda-lime glass substrates held at a substrate temperature of 673 K. Powder x-ray diffraction studies reveal that the films are polycrystalline in nature with chalcopyrite structure. The optical band gaps, calculated from spectral transmittance data, are found to be 1.56 ± 0.02 eV, 1.60 ± 0.02 eV and 1.85 ± 0.02 eV. Considering the three fold optical structure of chalcopyrite compounds, these are attributed to fundamental absorption and additional transitions arising out of crystal field and spin-orbit interactions. The crystal field (Δ_(CF)) and spin-orbit (Δ_(SO)) splitting parameters deduced from these optical band gaps are found to be -0.06 eV and 0.26 eV, respectively. The deformation potential estimated by using a quasi-cubic model is found to be -2.0 eV. The percentage of hybridization of the orbitals was determined using a linear hybridization model. The films are p-type conducting with a room temperature resistivity of 80 Ω cm.