Methanol solvent effect on photosensing performance of AZO thin films grown by nebulizer spray pyrolysis

Abstract

Dopant concentration variation or solvent change is commonly used for the growth and characterization of doped metallic thin films. In contrast, we have studied the effects of varying methanol solvent volume ratio for aluminum doped zinc oxide (AZO) thin film growth. AZO thin films were coated on glass and ITO substrates by nebulizer spray pyrolysis method. The effect of different solvent concentrations and the water to methanol ratio on the resultant film properties were analyzed. The structural and lattice constants of the prepared films were investigated by x-ray diffraction (XRD). Pure methanol solvent enhances the structural quality of the AZO film, as confirmed from the XRD and x-ray photoelectron spectroscopy analyses. The atomic force microscopy images showed thinner and smooth film surface for the pure methanol solvent condition without water. The optical absorption study showed a high transmittance (∼93%) in the visible region with a bandgap of 3.30 eV, which is close to bulk ZnO (3.36 eV). The photoluminescence spectra showed a powerful UV emission at 390 nm, indicating that the films were of good quality. Ag/AZO/Cu2O/ITO structured photodiodes were fabricated using ITO substrate and their photosensing properties were studied. All the prepared films (S1, S2, S3, S4 and S5) showed an increase in current level for both dark and light conditions, with an increase in methanol solvent ratio. The film S5 (pure methanol solvent) under the dark and light illumination conditions at a bias of 1.0 V, showed current values of ∼6.5 × 10–5 A and ∼1.85 × 10–4 A, respectively.