Structural, morphological, optical and photodetector properties of sprayed Li-doped ZnO thin films

Lithium-doped zinc oxide thin films (ZnO:Li) at different percentages (0-4%) were deposited on glass substrates at 460 A degrees C using the spray pyrolysis technique. The effect of lithium content on the structural, morphological and optical properties of ZnO:Li thin films was investigated. First, X-ray diffraction study revealed that undoped and Li-doped ZnO thin films crystallize in hexagonal wurtzite structure with a preferred orientation of the crystallites along (002) direction. The scanning electron microscopy (SEM) showed a clear hexagonal-shaped granular onto the surface of such films. Indeed, the averaged grain size, visualized by SEM, varied from 100 nm, for undoped ZnO, to 200 nm for ZnO:Li 4%. Second, the optical analysis by means of the transmittance and the reflectance measurements revealed that in UV-Vis domain, the average transmittance of the ZnO:Li thin films was 75%, while the average reflectance was < 35% in the visible range. Moreover, the band gap energy, E (g), decreased from 3.285 to 3.264 eV as Li content increases. On the other hand, the photoluminescence spectra revealed emission with multiple peaks and exhibited especially two emission bands in UV and visible regions. Finally, the ZnO photodetectors showed superior performance in the view of photocurrent.