Optoelectronic and low temperature thermoelectric effects in the OVC n-CuIn₃Se₅ thin films

Abstract

Optoelectronic properties and low temperature thermoelectric effects were studied on polycrystalline thin films of ternary chalcopyrite ordered vacancy compound (OVC) n-CuIn₃Se₅. The thin films prepared by three source vacuum co-evaporation method were preliminarily characterized structurally, morphologically, and compositionally by X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), respectively. Optical and optoelectronic measurements were done to obtain the band gap, carrier concentration, and photosensitivity of the materials. Thermopower dependence on temperature exhibited a non-degenerate semiconductivity, establishing Boltzmann statistics relation between carrier density and Fermi level in the films. While ionized impurity scattering has been detected near room temperature, an enhanced negative thermopower due to contribution from phonon drag has been noticed toward lower temperature in the films. Thermopower together with Hall coefficient and conductivity measurements permitted the correlation of density of states, carrier concentration, drift velocity, and the effective mass of the carriers with the conductivity of the films.