The electrical transport properties for compositionally and structurally well-defined epitaxial α-(Ti x Fe 1-x ) 2 O 3 (0001) films have been investigated for x ≤ 0.09. All films were grown by oxygen plasma assisted molecular beam epitaxy using two different growth rates -0.05 -0.06 Å/s and 0.22 -0.24 Å/s. Despite no detectable difference in cation valence and structural properties, films grown at the lower rate were highly resistive whereas those grown at the higher rate were semiconducting (ρ = ~1 Ω·cm at 25 o C). Hall effect measurements reveal carrier concentrations between 10 19 and 10 20 cm -3 at room temperature and mobilities in the range of 0.1 to 0.6 cm 2 /V·s for films grown at the higher rate. The conduction mechanism transitions from small-polaron hopping at higher temperatures to variable range hopping at a transition temperature between 180 to 140 K. The absence of conductivity in the slow-grown films is attributed to donor electron compensation by cation vacancies, which may form to a greater extent at the lower rate because of higher oxygen fugacity at the growth front.2

The properties of the ZnO thin films prepared by metalorganic vapor phase epitaxy under various oxygen partial pressures were thoroughly studied. It was found that the conduction type in undoped ZnO epilayers could be controlled by adjusting the family VI precursor, oxygen partial pressure during growth. The films were characteristic of n-type conductivity under oxygen partial pressure lower than 45 Pa. With the increase of oxygen content, the crystallinity of the ZnO thin films was degraded to polycrystalline with additional (10–12) orientation and the intrinsic p-type ZnO was produced as the oxygen partial pressure was larger than 55 Pa. The hole concentration and mobility could reach to 1.59×1016 cm−3 and 9.23 cm2 V−1 s−1, and the resistivity was 42.7 Ω cm. The near-band-edge emission and the deep level emission in photoluminescence (PL) spectra at room temperature were influenced strongly by the oxygen partial pressure. Temperature-dependent PL spectra in n-type ZnO films showed a dominant neutral-donor bound exciton emission, while p-ZnO was dominated by neutral-acceptor bound exciton emission. Both peaks increased in intensity with the decrease of the temperature and shifted to the short-wavelength side. The band that originated from zinc vacancies emerged at a temperature lower than 155 K only in the p-type films. The origin of intrinsic p-type conductivity in ZnO thin films might be related to zinc vacancy.

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