Heavy lithium-doped ZnO thin films prepared by spray pyrolysis method

Lithium-doped ZnO thin films (ZnO : Li x ) were prepared by spray pyrolysis method on the glass substrates for x (x = [Li]/[Zn]) value varied between 5 and 70%. Structural, electrical and optical properties of the samples were studied by X-ray diffraction (XRD), UV-Vis-NIR spectroscopy, scanning electron microscopy (SEM), Hall effect and sheet resistance measurements. XRD results show that for x ≤ 50%, the structure of the films tends to be polycrystals of wurtzite structure with preferred direction along (0 0 2). The best crystalline order is found at x = 20% and the crystal structure is stable until x = 60%. The Hall effect results describe that Li doping leads to change in the conduction type from n- to p-type, again it changes to n-type at x = 70% and is attributed to self-compensation effect. Moreover, the carrier density was calculated in the order of 1013 cm−3. The resistivity of Li-doped films decreases until 22 Ω cm at x = 50%. Optical bandgap was reduced slightly, from 3.27 to 3.24 eV as a function of the grain size. Optical transmittance in the visible range reaches T = 97%, by increasing of Li content until x = 20%. Electrical and optical properties are coherent with structural results.