Humidity Effects on the Electrical Properties of Epitaxial Rutile Thin Films

Abstract

ABSTRACTThin films of (001) and (100) oriented rutile phase TiO2, undoped or doped with Ga or Nb, have been grown using the MOCVD technique on sapphire substrates for use in studies of the effects of humidity on the electrical properties of rutile, lbe crystallographic and microstructural quality of the films decreases with increasing Ga and Nb concentrations. Heteroepitaxy is, however, maintained with Ga or Nb concentrations up to 4.5 at% for the (001) orientation and to 0.5 at% Ga for the (100) orientation. The electrical properties of the (001) oriented rutile films have been characterized from room temperature to 225 °C in dry and humid, N2 and air atmospheres. At constant temperature in dry atmospheres, the conductance of the Nb-doped rutile films is greater than that of the undoped, which is greater than the conductance of the Ga-doped films. The activation energies for conduction in die Nb-doped and undoped rutile films in dry atmospheres are similar (∼0.1 eV), whereas the activation energy in Ga-doped films is much greater (∼0.8 eV). The effects of humidity in reducing the resistance of rutile is greatest in the Ga-doped and very min (∼150 Å) undoped films. Humidity is observed to have similar effects on both the (001) and (100) oriented 0.5 at% Ga-doped films.