Effect of lithium doping on microstructural and optical properties of zno nanocrystalline films prepared by the sol-gel method

The Zn_1−x Li_x O (x = 0, 0.01, 0.03, and 0.05) nanocrystalline films were synthesized on silicon (Si) substrates by using the sol-gel method. The crystal structure and surface morphology of these films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). We observed that the average grain size was gradually reduced with increasing doping Li content. Photoluminescence (PL) spectra show that increasing the Li content will deteriorate the crystalline quality and result in the decrease of ultraviolet emission from the excitonic recombination and the enhancement of visible emission from the recombination between the intrinsic defects. The current-voltage properties of Zn_1−x Li_x O nanocrystalline films were also studied under dark and photo-illumination for photo-detection applications. The normalized photo-to-dark-current ratio (I_photo − I_dark)/I_dark has been enhanced from 315 to 4161 by increasing the Li content of the Zn_1−x Li_x O nanocrystalline films from zero to 0.05.