Effect of doping concentration and substrate temperature on the physical properties of Indium-doped zinc oxide thin films

Conductive and transparent Indium-doped zinc oxide (ZnO:In) thin films were deposited on glass substrates by the ultrasonic spray pyrolysis technique. Films were prepared from 0.2 M starting solutions of zinc acetate dissolved in a mixture of water, acetic acid and methanol. Indium acetate was used as In source at three different atomic concentrations, namely, 1, 2, and 3 at %. The effect of the Indium concentration in the starting solution on the electrical, structural, morphological, and optical characteristics of the films was studied. Electrical resistivity as low as 2×10^-3Ωcm, electron mobility around 12 cm²/(V-s), carrier concentration in the range 2.19-3.4 ×10²⁰cm^-3, and an optical transmittance in the range 65-75 % were achieved for 3 at % ZnO:In thin films. All films were polycrystalline, growing preferentially along the (002) and (101) directions, depending on the indium concentration in the starting solution. Shape and grain size, were dependent on the [In/Zn] ratio in the starting solutions as well.