Effects of withdrawal speed on the microstructural and optical properties of sol-gel grown ZnO:Al thin films

Nanocrystalline Al-doped ZnO (AZO) thin films were deposited on glass substrates by using sol-gel dip coating technique at different withdrawal speeds (WS: 20, 40 and 80 mm/min). The effects of WS on the crystalline structure, morphology and optical properties of the obtained films were extensively investigated using a series of characterization techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and photoluminescence (PL). It was found that, the WS significantly affects the crystalline structure, morphology and optical properties of the films. XRD analysis confirmed that the films are polycrystalline in nature having hexagonal crystal structure with preferred grain orientations along (100), (002) and (101) directions. SEM and AFM observations indicate a smooth surface morphology with small rounded grains. The optical band-gap energy (Eg) was evaluated as 3.20-3.27 eV, which increased with increasing withdrawal rate. At room temperature, a photoluminescence was observed from AZO thin films and the origin of the emission was discussed.