Electrical and Optical Studies of Lithium and Cobalt co-doped ZnO Thin Films Fabricated by Pulsed Laser Deposition

Abstract

We characterize the physically produced Li-doped ZnO having concentration of lithium 2,4,6 and 8% and Li co-doped (Zn, Co)O in which cobalt concentration is fixed at 4% thin films fabricated by pulsed laser deposition technique. The effect of lithium doping in pure ZnO and in ZC4 is investigated. Electrical and optical properties of samples were studied by Hall Measurements which include measurement of sheet resistance, resistivity, conductivity, mobility and carrier concentration. Spectroscopic ellipsometry was done for optical studies, by modelling the ellipsometry spectra we get reflection and extinction coefficient, refractive index, dielectric constants, amplitude and phase ratio along with thickness. Zinc oxide has a hexagonal wurtzite crystal structure, optical bandgap is calculated by Beer Lambert Law it is observed that by increasing doping concentration optical bandgap increases. From the results of Hall measurements, it is observed that change in the conduction type from n- to p-type is due to Li doping. Resistivity decreases sharply at 4% lithium co-doping due to which conductivity is increased. From temperature independent ellipsometry results it is concluded that values of extinction coefficient and refractive index and started decreasing as wavelength increase, sharp peaks were observed in visible region. The crystalline structure of ZnO can be improved by lithium doping and can be used in the Organic Light Emitting Diodes. Li doping enhanced device performance and luminescence and can be used for fabrication of OLEDs. This material could be used in light emitting diodes in nanoscale optoelectronic devices.