The defect structure of barium titanium oxide thin films

The defect structure of high purity BaTiO{dollar}sb3{dollar} thin films was investigated. BaTiO3 thin films were grown on MgO (100), LaAlO{dollar}sb3{dollar} (100), SiO{dollar}sb2{dollar}/Si, and Pt/MgO substrates using low pressure, metalorganic chemical vapor deposition. The experimental parameters for the deposition of single phase BaTiO{dollar}sb3{dollar} films were optimized; these include the reactant partial pressure, deposition temperature and choice of substrate material. Both epitaxial and polycrystalline films were prepared.; Electrical and optical measurements including resistivity, thermopower, temperature dependent resistivity, and transient photocapacitance spectroscopy, were used to determine the defect structure of the BaTiO{dollar}sb3{dollar} thin films. Evidence for activated mobility was found; therefore, a modified polaron conduction model was applied to the electrical data. The activation energy for polaron conduction decreased from 0.2-0.1eV as the impurity concentration increased, which indicates a variable range hopping mechanism.; The electrical resistivity and transient photocapacitance were sensitive to the purity of the films. The high purity, as-grown films had resistivities ranging from 10{dollar}sp5{dollar}-10{dollar}sp7{dollar} {dollar}Omega{dollar}-cm. The transient photocapacitance spectra of these films were dominated by deep levels (10{dollar}sp{lcub}13{rcub}{dollar}-10{dollar}sp{lcub}14{rcub}{dollar}cm{dollar}sp{lcub}-3{rcub}{dollar}) with ionization energies ranging from E{dollar}sb{lcub}rm v{rcub}{dollar} + 2.95-3.3 eV. These defect levels were attributed to native oxygen vacancy donors since their concentration increased with vacuum reduction. However, films deposited with a lower purity precursor ({dollar}rho{dollar} = 10{dollar}sp2{dollar}-10{dollar}sp4Omega{dollar}-cm) contained several other traps ({dollar}rm 10sp{lcub}14{rcub}cmsp{lcub}-3{rcub}{dollar}) deeper within the band gap of BaTiO{dollar}sb3{dollar} at energies of E{dollar}sb{lcub}rm v{rcub}{dollar} + 1.8, E{dollar}sb{lcub}rm v{rcub}{dollar} + 2.1eV, E{dollar}sb{lcub}rm v{rcub}{dollar} + 2.4, E{dollar}sb{lcub}rm v{rcub}{dollar} + 2.6-2.7eV in addition to the oxygen vacancies ({dollar}rm 10sp{lcub}13{rcub}{dollar}-{dollar}10sp{lcub}14{rcub}rm cmsp{lcub}-3{rcub}{dollar}) at E{dollar}sb{lcub}rm v{rcub}{dollar} + 2.95-3.3eV. The mid-gap levels were ascribed to unintentional, Fe impurities.; Point defect equilibrium models were developed for the BaTiO{dollar}sb3{dollar} films from the above measurements. A doubly ionized oxygen vacancy model, which is compensated by acceptors describes the defect equilibria for both high and low purity BaTiO{dollar}sb3{dollar} films. No evidence of self compensation by barium or titanium vacancies was found in the high purity or doped films.