C. Ke

Heteroepitaxial growth of SnO2 thin films on SrTiO3 (111) single crystal substrate by laser molecular beam epitaxy

SnO2 films with a thickness around 150 nm were deposited on the (111) surface of a SrTiO3 single crystal substrate by laser molecular beam epitaxy technique in a temperature range 600–750 °C and oxygen pressure from 10−3 to 1 Pa, respectively. The growth behavior was in situ monitored by reflection high-energy electron diffraction, and the epitaxial relations were further investigated by ex situ x-ray diffraction measurement in different geometries. All the films were confirmed to be highly (200) oriented showing good crystalline quality, despite the large lattice mismatch between SnO2 and SrTiO3. Based on the crystallographic model and structure analysis, six equivalent directions in the SrTiO3 (111) surface for the nucleation of SnO2 were discovered, which confirmed the existence of sixfold symmetrical domains in the SnO2 epilayer. Additionally, the optical dielectric function of the SnO2/SrTiO3 epitaxial film was simulated by the Tauc–Lorentz–Drude model in the UV-vis-NIR region.

Thickness-Induced Metal-Insulator Transition in Sb-doped SnO2 Ultrathin Films: The Role of Quantum Confinement.

A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

Annealing induced anomalous electrical transport behavior in SnO2 thin films prepared by pulsed laser deposition

SnO2 thin films were deposited on quartz substrates by pulsed laser deposition and postannealed at different temperatures in oxygen ambience. X-ray diffraction, Hall measurement, and x-ray photoelectron spectroscopy were employed to investigate the properties of the annealed SnO2 thin films. An anomalous electrical transport behavior as a function of the annealing temperature was observed. Both the growth of the crystal grain and oxygen vacancy density variation in the annealing process have been identified to be responsible for the transition of electrical transport properties.