Influence of thermal cycling on the optical and the electrical properties of atmospheric pressure chemical vapor deposited tin oxide films grown using water and methanol vapors as oxidizers

Abstract

Tin oxide films were chemically vapor deposited at atmospheric pressure at temperatures near 400 °C using SnCl4 as metal precursor and water or methanol vapors as oxidizers. The optical and electrical properties of these films were studied with spectroscopic ellipsometry (SE) and resistivity measurements while morphology and structure by scanning electron microscopy (SEM) and x-ray diffraction (XRD) measurements. It was found that both kinds of samples exhibited granular morphology with grain sizes of 10 and 80-100 nm for water and methanol deposited samples respectively. The crystallographic orientation of grains was similar for both kinds of samples. SE and resistivity measurements were simultaneously performed on samples up to 400 °C in air and at two thermal cycles. Using the Tauc-Lorentz combined with the Drude physical models the refractive index (real and imaginary parts) and the Tauc gap of samples were extracted from the SE measurements. Films morphology proved to be the decisive factor that governs optical and electrical properties of SnO2 films. So, large gained methanol vapor deposited SnO2 films were more than 80% transparent within the visible and an order of magnitude more conductive (resistivity of the order of 9-10 mΩ.cm) than the water deposited small-grained ones. It was also found that thermal cycling causes slight atomic re-arrangements in films that are invisible in XRD and SEM measurements but which influence significantly their optical and electrical properties.