Abstract
Thin films of (SnO2: MnO2) with different doping ratios (2, 4, 6, 8%) were prepared by depositing them on glass substrates at a temperature of 350°C and a thickness of (250±50) nm using the chemical spray pyrolysis (CSP) technique. The structural, optical and electrical properties of all the prepared films were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), UV-Visible Spectroscopy, Hall Effect, and dark conductivity (I-V) characteristics. The XRD results showed that all the prepared films have a polycrystalline structure with a predominant (110) orientation and the SnO2 film has a tetragonal structure. The AFM results indicated that the average roughness and root mean square (RMS) roughness values increase with increasing MnO2 doping ratio. The FE-SEM examination revealed that the surface morphology of the prepared films consists of non-homogeneous agglomerates, and the agglomerate size of these particles decreases with increasing MnO2 doping ratio, which is attributed to the diffusion of manganese atoms within the SnO2 crystalline lattice. The optical characterization using UV-Visible spectroscopy in the wavelength range of (300-1100) nm showed that the prepared films have an optical band gap ranging from 3.5 to 5 eV, and the transmittance values decreased while the absorbance values increases with increasing MnO2 doping ratio. The reflectance, absorption coefficient, refractive index, extinction coefficient, and real and imaginary parts of the optical dielectric constant were also calculated. The electrical measurements using the Hall Effect showed that the prepared undoped and MnO2-doped thin films have n-type charge carriers, and the films exhibit high resistivity and low conductivity.
The (I-V) measurements of the heterojunction (p-SnO2:MnO2/n-Si) showed that the dark current in the case of forward bias variation with the change in the applied voltage and that the saturation current increases with the increase in doping with the decrease in the ideality factor with the increase in doping.
