The influence of oxygen flow rate on properties of SnO2 thin films grown epitaxially on c-sapphire by chemical vapor deposition

• SnI2 (Sn2 +) was used as tin precursor to prepare tin oxide films by CVD.
• Epitaxial SnO2 (100) films were obtained on c-sapphire with thickness more than 1 μm.
• The epitaxial relationship is SnO2(100)||Al2O3(0001) and SnO2[010]||Al2O3< 11–20 >.
• B2g Raman mode was found to be absent in (100)-orientated SnO2 films on c-sapphire.
• The crystal quality and properties of SnO2 films depended sensitively on the O2 flow rate.

Tin dioxide (SnO2) thin films were grown on c-plane sapphire substrates by chemical vapor deposition using SnI2 and O2 as reactants. The growth experiments were carried out at a fixed substrate temperature of 510 °C and different O2 flow rates. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, UV–Vis–IR spectrophotometry and Hall-effect measurement were used to characterize the films. All films consisted of pure-phase SnO2 with a rutile structure and showed an epitaxial relationship with the substrate of SnO2(100)||Al2O3(0001) and SnO2[010]||Al2O3< 11–20 >. The crystalline quality and properties of the films were found to be sensitively dependent on the O2 flow rate during the film growth. The absolute average transmittance of the SnO2 films exceeded 85% in the visible and infrared spectral region. The films had optical band-gaps (3.72–3.89 eV) that are in line with the band gap of single-crystal SnO2. The carrier concentration and Hall mobility of the films decreased from 3.3 × 1019 to 9 × 1017 cm− 3 and from 19 to 2 cm2 V− 1 s− 1, respectively, while the resistivity increased from 0.01 to 3 Ω cm with increasing of the O2 flow rate from 5 to 60 sccm.