Nanocrystalline SnO2 thin films: Structural, morphological, electrical transport and optical studies

Abstract

Sol–gel spin coating method has been successfully employed for preparation of nanocrystalline tin oxide (SnO2) thin films. The effect of processing temperature on the structure, morphology, electrical conductivity, thermoelectric power and band gap was studied using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction pattern, atomic force microscopy, two probe technique and UV–visible spectroscopy. X-ray diffraction (XRD) analysis showed that SnO2 films are crystallized in the tetragonal phase and present a random orientation. Field emission scanning electron microscopy (FESEM) analysis revealed that surface morphology of the tin oxide film consists nanocrystalline grains with uniform coverage of the substrate surface. Transmission electron microscopy (TEM) of SnO2 film showed nanocrystals having diameter ranging from 5 to 10nm. Selected area electron diffraction (SAED) pattern confirms tetragonal phase evolution of SnO2. Atomic force microscopy (AFM) analysis showed surface morphology of SnO2 film is smooth. The dc electrical conductivity showed the semiconducting nature with room temperature electrical conductivity increased from 10−7 to 10−5 (Ωcm)−1 as processing temperature increased from 400 to 700°C. Thermo power measurement confirms n-type conduction. The band gap energy of SnO2 film decreased from 3.88 to 3.60eV as processing temperature increased from 400 to 700°C.