Y. Bharath Kumar Reddy

Growth and characterization of CuIn1−xAlxSe2 thin films deposited by co-evaporation

CuIn1−xAlxSe2 thin films (x = 0–1.0) were prepared by the four-source co-evaporation technique onto soda lime glass substrates held at 673 K. The films are found to be nearly stoichiometric as determined from Rutherford back scattering (RBS) analysis. Surface analysis of the films was carried out by x-ray photoelectron spectroscopy. X-ray diffraction and scanning electron microscopy are used to examine the structure of the films. The films are found to be single phase and chalcopyrite in structure. The lattice parameters are found to vary nonlinearly with x. Optical absorption studies reveal a three-fold optical band structure and the band gaps are found to increase nonlinearly with the increase in Al content. Crystal field and spin–orbit parameters are determined from the band gaps using a quasi-cubic model. The deformation potential and the percentage of d-orbital contribution to p–d hybridization are determined using the deduced crystal field and spin-orbit parameters. All the films are p-type conducting and the resistivity is found to increase with the increase in Al content. Room temperature Hall mobility and the carrier concentration of the films are determined.

Optical and structural properties of co-evaporated CuIn0.5Al0.5Se2 thin films

CuIn0.5Al0.5Se2 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 (ΔCF) and spin–orbit (ΔSO) 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.