Structural and Electrical Characterization of ZnO Films Grown by Spray Pyrolysis and Their Application in Thin- Film Transistors

摘要

The role of the substrate temperature on the structural, optical, and electronic properties of ZnO thin films deposited by spray pyrolysis using a zinc acetate precursor solution is reported. Analysis of the precursor compound using thermogravimentry and differential scanning calorimetry indicates complete decomposition of the precursor at around 350 ℃. Film characterization using Fourier Transform Infrared Spectroscopy (FTIR), photoluminescence spectros-copy (PL), and ultraviolet-visible (UV-Vis) optical transmission spectroscopy suggests the onset of ZnO growth at temperatures as low as 100 ℃ as well as the transformation to a polycrystalline phase at deposition temperatures >200 ℃. Atomic force microscopy (AFM) and X-ray diffraction (XRD) reveal that as-deposited films exhibit low surface roughness (rms ≈ 2.9 nm at 500 C) and a crystal size that is monotonously increasing from 8 to 32 nm for deposition temperatures in the range of 200-500 ℃. The latter appears to have a direct impact on the field-effect electron mobility, which is found to increase with increasing ZnO crystal size. The maximum mobility and current on/off ratio is obtained from thin-film transistors fabricated using ZnO films deposited at >400 ℃ yielding values on the order of 25 cm~2 V~(-1)s~(-1) and 10~6, respectively.