Optical and electrical properties of Bi doped ZnO thin films deposited by ultrasonic spray pyrolysis

Undoped Zinc oxide (ZnO) and Bismuth doped zinc oxide (ZBO) thin films have been prepared by a simple and inexpensive technique namely ultrasonic spray pyrolysis. Films were prepared from an aqueous solution of zinc acetate on glass and silicon substrates at temperature of 350 A degrees C. Doping is achieved by adding a small amount of Bi(NO3), H2O salt to the starting solution which is mixed thoroughly prior to spraying. The goal of this work is to study the influence of doping (Bi) with different concentrations on the structural, optical, and electrical properties of Bi doped ZnO films. Structural analysis shows that the ZBO layers are polycrystalline with a wurtzite structure and (100) preferential orientation which disappears gradually with increasing doping concentration. The optical transmittance average of all films, regardless the doping concentration, was higher than 80% in the visible range. The obtained films gaps values vary in the range from 3.19 to 3.24 eV and the Urbach energy lies in the range 11 to 530 meV. The measured conductivity, in dark and at room temperature, varies with four order of decade level (from 10(-3) to 10(+1) (a"broken vertical bar cm)(-1))with increasing Bi doping level.