Structural, optical, and dielectric characteristics of pulsed laser deposited SnO₂-TiO₂ composite thin films

Abstract

Pulsed laser deposition was used to fabricate the thin films of SnO2 and SnO2-TiO2 composites on FTO substrates and these films were characterized to understand the effect of TiO2 on the structural, optical, and electrical properties of SnO2. The crystalline nature, phase purity, and optical bandgap were determined using X-ray diffraction and UV-Vis measurements, respectively. The Tauc plots confirm that the composite films have a higher band gap energy than SnO2. EDX spectra demonstrate that the thin films contain Ti, Sn, and O ions. The photoluminescence (PL) spectra indicate three blue emission bands at wavelengths of 410, 435, and 460 nm and these are due to the oxygen vacancies or interstitial oxygen ions and defect related states formed during the thin-film deposition of SnO2 and composites. These films are n-type semiconductors as verified by the Hall Effect measurements. At the interface of the film, the frequency dependence of the dielectric at room temperature reveals that as the frequency increases, the dielectric constant and dielectric losses decrease. SnO2 film has a significantly higher a.c. conductivity than the SnO2-TiO2 composite films. The correlated barrier hopping (CBH) mechanism is responsible for the conduction behaviour and obeys Johncher's power law (n<1). Both films exhibit a frequency-dependent increase in impedance. The addition of TiO2 in SnO2 affects the structural, optical, dielectric, and ac conductivity of films at room temperature. These optical and n-type semiconducting nature supports the potential application in microelectronics, optoelectronics, and sensor applications.