Characterization of SnO2 Thin Films Fabricated by Chemical Spray Pyrolysis

Abstract

In the last few years, synthesis of inexpensive tin dioxide films gained a big deal of interest, because they have a large optical band gap (Eg>3 eV), and a n-type semiconductor behavior. In this work, SnO2 thin films were deposited at 400 °C on Silica glass (SiO2) substrates during 30 min by spray pyrolysis technique. Then, prepared films were annealed in air at temperatures of 400 °C, 450 °C and 500 °C for 1h. The effect of annealing treatments on the structural, morphological, and optical properties of films have been studied using X-Ray Diffraction (XRD), Raman scattering spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and UV-Visible spectrophotometry, respectively. X-ray diffraction patterns indicated that tin dioxide thin films had a polycrystalline tetragonal rutile structure. The crystallite size increases with annealing temperature. This study was also confirmed by Raman scattering characterization. Morphological analysis showed that the grains were agglomerated with an island-like structure over the entire surface of substrates. As-deposited films showed agglomerates of different shapes varying in the range 0.2 µm - 1 µm, while annealed films revealed ones spherical in shape varying from 0.6 µm to 1.2 µm. Elementary composition of samples were observed by energy dispersive X-ray spectroscopy (EDX). Root Mean Squared high (RMS) obtained from AFM decreased from 212 nm to 202 nm after annealing. Despite the fact that optical characteristics have revealed low transmittance values (≈ 27%), the deposited films exhibited large optical gap (Eg ≈ 3.75 eV) even after annealing at 500 °C. This study showed by XRD that the crystallites sizes increased with increasing of annealing temperature and this result was confirmed by SEM analysis. Also, this work can help to improve and control the deposition parameters of SnO2 sprayed thin films in order to synthesis promising materials for energy.