Gas sensing properties of epitaxial SnO2 thin films prepared by atomic layer deposition

Undoped SnO2 thin films are grown on α-Al2O3(0 1 2) (r-cut sapphire) substrates by gas phase atomic layer deposition (ALD). Two precursor pairs, SnI4–O2 and SnCl4–H2O2, both new for ALD, are used. The films have a cassiterite structure and are (1 0 1)[0 1 0]cassiterite||(0 1 2)[1 0 0]sapphire oriented. A good epitaxial quality and the conductivity acceptable from the standpoint of semiconductor gas sensors are achieved for ultrathin films grown from SnI4–O2 at 600 °C. The sensitivity of these films to CO in air has a maximum at a thickness of about 10 nm. Response rise and decay times belonging to a several seconds interval are measured. The films are assumed to function as a single grain.