Structural, electrical and optical properties of solution grown polycrystalline Cu_1-xAg_xSe thin films

Abstract

Polycrystalline thin films of Cu1-xAgxSe (0<or=x<or=1) have been deposited by a 'solution growth' technique. As-deposited films have been annealed at different temperatures up to 500 K and the appearance of electrical conductivity has been observed. The electrical conductivity of annealed films shows an exponential dependence on temperature, and two thermal activation energies have been calculated. Excluding x=0, all the films displayed n-type conductivity. Carrier concentration, mobility and thermoelectric power measurements of these films have been carried out as a function of composition. X-ray analysis indicates that CuSe and AgSe films have a cubic crystal structure while films with 0.1<or=x<or=0.9 possess a tetragonal structure with axial ratio approximately 1.25. Films of stoichiometry 0.1<or=x<or=1 show both a direct and an indirect optical bandgap Eg from 1.4 to 1.37 eV and from 1.19 to 0.99 eV respectively. Other parameters such as absorption coefficient alpha , refractive index n, dielectric constant epsilon , and extinction coefficient k have also been computed from reflectance and transmittance spectra.