The atomic layer deposition (ALD) of stoichiometric SrTiO3 as well as layers with either Sr or Ti excess from the commercial precursors Bis(tri-isopropylcyclopentadienyl)-strontium Sr(iPr3Cp)2, Tetrakis-(dimethylamido)titanium(IV) Ti[N(CH3)2]4 and H2O on a commercial ALD system is demonstrated. The influence of the stoichiometry on the optical layer properties was investigated. Spectroscopic ellipsometry shows that all SrxTiyOz layers are transparent up to the optical gap energy, which amounts to 3.87eV for stoichiometric SrTiO3. A direct correlation between the Sr content, optical properties, layer density and the growth per cycle value was determined. X-ray photoelectron spectroscopy after Ar ion cluster sputtering indicates that the layers are free of carbon. After ex situ annealing under atmospheric conditions we observed a change in microstructure from amorphous to polycrystalline starting at 545°C by atomic force microscopy and grazing incidence X-ray diffraction. Electrical I–V measurements show very small leakage currents confirming the insulating character of the SrxTiyOz layers.

Strontium titanate is a promising insulator material in resistance switching random access memories. Strontium titanate thin films are prepared by atomic layer deposition from bis(tri-isopropylcyclopentadienyl)-strontium (Sr(iPr3Cp)2), Tetrakis-(dimethylamido)titanium(IV) (Ti[N(CH3)2]4) and water at a substrate temperature of 300°C. The layer stoichiometry is analyzed by X-ray fluorescence spectroscopy for the main element composition and by X-ray photoelectron spectroscopy to detect light element contamination. A significant carbon contamination is found whereas nitrogen is not detected. These results are discussed with possible decomposition reactions of the Sr(iPr3Cp)2 molecule at the given deposition temperature. The film microstructure is characterized by grazing incidence X-ray diffraction. Optical and electrical characterizations show that the strontium titanate layers are transparent up to an optical gap of 3.85eV and insulating.

The atomic layer deposition (ALD) of TiO2 from tetrakis(dimethylamino) titanium(TDMAT) and water was studied in the substrate temperature (T-S) range of 120 degrees C to 330 degrees C.The effect of deposition temperatures on the resulting layer microstructure is investigated. Based on the experimental results, possible interaction mechanisms of TDMAT and H2O precursor molecules and the TiO2 surface at different temperatures are discussed. The TiO2 layers were characterized with respect to microstructure, composition and optical properties by glancing angle x-ray diffraction and reflectometry, x-ray fluorescence analysis, photoelectron spectroscopy and spectroscopic ellipsometry. A constant layer growth with increasing number of ALD cycles was achieved for all investigated deposition temperatures, if the inert gas purge time after the H2O pulse was increased from 5 s at temperatures below 250 degrees C to 25 s for T-S >= 320 degrees C. In the investigated temperature range, the growth per cycle varies between 0.33 and 0.67 angstrom/cycle with a minimum at 250 degrees C. The variations of the deposition rate are related to a change from a surface determined decomposition of TDMAT to a gas phase decomposition route above 250 degrees C. At the same temperature, the microstructure of the TiO2 layers changes from amorphous to predominately crystalline, where both anatase and rutile are present. (C) 2013 Elsevier B. V. All rights reserved.

In this chapter, VE- positron annihilation lifetime spectroscopy (PALS) measurements are reported on a series of Fe-doped SrTiO3 (STO) thin films grown by pulsed laser deposition (PLD). Fe-doped SrTiO3 thin films provide an insightful model system for the study of resistive switching memory device mechanisms. The chapter presents the ab initio calculations to address the defect structure of β-Ga2O3. Homoepitaxial STO thin films are a suitable oxide model system to investigate the effect of defects on the electrical properties. The initial conductivity of STO can be enhanced by introduction of donor or acceptor dopants or intrinsic point defects by increasing the oxygen vacancy concentration. Bulk polycrystalline thermistor ceramics on BaTiO3-basis with positive temperature coefficient (PTC) posses an increasing current limiting electric insulation resistance when they are heated above the Curie temperature Tc of the ferroelectric compound BaTiO3. Acceptor doped LaMO3 materials have attractive magnetic and electrical properties and possess ferroelasticity. Controlled Vocabulary Terms ceramics; ferroelectric materials; oxygen; switching; thin films

Vacuum annealing is a widely used method to increase the electric conductivity of SrTiO3 single crystals. The induced oxygen vacancies act as intrinsic donors and lead to n-type conductivity. Apart from the changed electronic structure, however, also crystal structure modifications arise from this treatment. Hence, electronic properties are determined by the interplay between point defects and line defects. The present paper provides a survey of the real structure of commercially available SrTiO3 single crystals and the changes induced by reducing vacuum heat-treatment. Therefore, all investigations were performed ex situ, i.e., after the annealing process. Used characterization methods include atomic force microscopy, transmission electron microscopy, spectroscopic ellipsometry, infrared spectroscopy, and photoluminescence spectroscopy. Besides the expected variation of bulk properties, especially surface modifications have been detected. The intrinsic number of near-surface dislocations in the samples was reduced by vacuum annealing. X-ray photoelectron spectroscopy proves the existence of a layer of adsorbed molecules, which influences the SrTiO3 work function. Also, the interaction between adsorbates and surface point defects as well as laser annealing due to local oxygen absorption are discussed.

Electrical properties of SrTiO3 single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated in the temperature range of 35 K–300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping. Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature T C at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously pin tetragonal domains. Thus, microregions of the tetragonal phase persist above T C causing the hysteresis in resistivity up to ∼12%. This effect possibly provides new chances for future oxide based non-volatile data-storage devices.