Negative Differential Resistance Induced by Mn Substitution at SrRuO3/Nb:SrTiO3 Schottky Interfaces

We observed a strong modulation in the current-voltage characteristics of SrRuO$_3$/Nb:SrTiO$_3$ Schottky junctions by Mn substitution in SrRuO$_3$, which induces a metal-insulator transition in bulk. The temperature dependence of the junction ideality factor indicates an increased spatial inhomogeneity of the interface potential with substitution. Furthermore, negative differential resistance was observed at low temperatures, indicating the formation of a resonant state by Mn substitution. By spatially varying the position of the Mn dopants across the interface with single unit cell control, we can isolate the origin of this resonant state to the interface SrRuO$_3$ layer. These results demonstrate a conceptually different approach to controlling interface states by utilizing the highly sensitive response of conducting perovskites to impurities

Coexistence of two- and three-dimensional Shubnikov-de Haas oscillations in Ar^+ -irradiated KTaO_3

We report the electron doping in the surface vicinity of KTaO_3 by inducing oxygen-vacancies via Ar^+ -irradiation. The doped electrons have high mobility (> 10^4 cm^2/Vs) at low temperatures, and exhibit Shubnikov-de Haas oscillations with both two- and three-dimensional components. A disparity of the extracted in-plane effective mass, compared to the bulk values, suggests mixing of the orbital characters. Our observations demonstrate that Ar^+ -irradiation serves as a flexible tool to study low dimensional quantum transport in 5d semiconducting oxides

PROPOSAL OF NEW K-FACTOR FUNCTION IN LIGHTNING IMPULSE TEST FOR ELECTRIC POWER EQUIPMENT

Ultra high voltage (UHV) systems are increasingly being planned and constructed, hence studies are promoted on the standard for high-voltage test techniques for UHV-class equipment. For the lightning impulse voltage test, a study is being conducted on the application of a method of evaluating the test waveform through conversion using the test voltage function (k-factor function) that was adopted in IEC 60060-1. The existing k-factor function was established based on the experimental results for more compact models, as compared with the insulating structure of UHV-class equipment, mainly with a breakdown voltage of about 100 kV. To determine whether this k-factor function can also be used for the test of UHV-class equipment, the experimental results for large-sized models were needed. In the present paper, to address this issue, the authors initially obtained k-factor values experimentally using the largest possible model (UHV model) assuming UHV-class equipment. Substantially, a study was conducted on a new k-factor function based on these experimental results. First, in the study, several ideas for the k-factor function were shown and applied to various waveforms to clarify their advantages and disadvantages. Next, in addition to these results, a study was conducted on a k-factor function suitable for UHV-class equipment with considering the actual UHV facilities. Consequently, it was concluded that the form of the function should be the same as that of the existing one but that it would be reasonable to adopt a relatively lower k-factor function for UHV-class equipment by revising the constant. Further, this new function could replace the existing one in 60060-1 for all voltage classes to consider the breakdown voltage ranges as a basis and LIWV (Lightning Impulse Withstand Voltage) values.20th International Symposium on High Voltage Engineering, August 28 - September 01, 2017, Buenos Aires, Argentin

Metal-to-insulator transition in anatase TiO2 thin films induced by growth rate modulation

We demonstrate control of the carrier density of single phase anatase TiO2 thin films by nearly two orders of magnitude by modulating the growth kinetics during pulsed laser deposition, under fixed thermodynamic conditions. The resistivity and the intensity of the photoluminescence spectra of these TiO2 samples, both of which correlate with the number of oxygen vacancies, are shown to depend strongly on the growth rate. A quantitative model is used to explain the carrier density changes.Comment: 13 pages 3 figure

A Heteroepitaxial Perovskite Metal-Base Transistor

'More than Moore' captures a concept for overcoming limitations in silicon electronics by incorporating new functionalities in the constituent materials. Perovskite oxides are candidates because of their vast array of physical properties in a common structure. They also enable new electronic devices based on strongly-correlated electrons. The field effect transistor and its derivatives have been the principal oxide devices investigated thus far, but another option is available in a different geometry: if the current is perpendicular to the interface, the strong internal electric fields generated at back-to-back heterojunctions can be used for oxide electronics, analogous to bipolar transistors. Here we demonstrate a perovskite heteroepitaxial metal-base transistor operating at room temperature, enabled by interface dipole engineering. Analysis of many devices quantifies the evolution from hot-electron to permeable-base behaviour. This device provides a platform for incorporating the exotic ground states of perovskite oxides, as well as novel electronic phases at their interfaces

Optically tuned dimensionality crossover in photocarrier-doped SrTiO3_3: onset of weak localization

We report magnetotransport properties of photogenerated electrons in undoped SrTiO$_3$ single crystals under ultraviolet illumination down to 2 K. By tuning the light intensity, the steady state carrier density can be controlled, while tuning the wavelength controls the effective electronic thickness by modulating the optical penetration depth. At short wavelengths, when the sheet conductance is close to the two-dimensional Mott minimum conductivity we have observed critical behavior characteristic of weak localization. Negative magnetoresistance at low magnetic field is highly anisotropic, indicating quasi-two-dimensional electronic transport. The high mobility of photogenerated electrons in SrTiO$_3$ allows continuous tuning of the effective electronic dimensionality by photoexcitation.Comment: 7 pages, 7 figure

Characterization of the Schottky Barrier in SrRuO3/Nb:SrTiO3 Junctions

Internal photoemission spectroscopy was used to determine the Schottky barrier height in rectifying SrRuO3/Nb-doped SrTiO3 junctions for 0.01 wt % and 0.5 wt % Nb concentrations. Good agreement was obtained with the barrier height deduced from capacitance-voltage measurements, provided that a model of the nonlinear permittivity of SrTiO3 was incorporated in extrapolating the built-in potential, particularly for high Nb concentrations. Given the generic polarizability of perovskites under internal/external electric fields, internal photoemission provides a valuable independent probe of the interface electronic structure.Comment: 15 pages, 3 figure