Field-effect Configuration Research Articles

Field Effects in Thin Films of Manganites Using a Planar Field Effect Configuration

Modulation of the metal-insulator phase transition of perovskite manganite oxides is achieved by a static electric field. The field is applied using a planar field-effect configuration, which was formed on a monolayer film. In such a field-effect configuration, La1−xAxMnO3 film is used as the channel and substrate acts as the gate. Both divalence-doped (La0.7Ba0.3MnO3, Pr0.7Sr0.3MnO3), and tetravalence-doped (La0.7Ce0.3MnO3) systems demonstrate significant field effects. The field modulations are found being nonlinear and polarity dependent on the applied bias. The results obtained in La0.7Ce0.3MnO3 indicates that electron doped manganites have similar features as those found in hole doped manganites. The observed field effects were discussed with the percolative phase separation picture.

High resistance modulation by the electric field based on La0.9Sr0.1MnO3/SrTiO3/Si structure

A field-effect configuration based on La0.9Sr0.1MnO3/SrTiO3/Si structure is fabricated on Si substrate by laser molecular-beam epitaxy. The resistance modulation by electric field of the La0.9Sr0.1MnO3/SrTiO3/Si structure is investigated in detail. An evident resistance modulation effect is observed at 80 K. The channel resistance modulation by field effect reaches 1.4×107% and 2.6×106% when V DS are −2 and −6.5 V, respectively. The ON/OFF ratio of approximately 4000 is obtained. The present results are worthy of further investigations for potential applications of resistance modulation by electrostatic field in the heterostructures consisting of perovskite oxides and Si.

The Response of Transport Properties to Static Electric Field in La$_{0.7}$Ce$_{0.3}$MnO$_{3}$ Epitaxial Thin Films

We investigated the influence of static electric field on the transport properties in La0.7Ce0.3MnO3 epitaxial thin films by using a simple field effect configuration (FEC), which was formed on a single layer film. Substrates act as gates and films as channels. Such an easily manipulative technique avoids many possible problems appeared in multilayer structures, such as poor interface and severe inter-diffusion, which may influence the intrinsic characteristics of investigated targets. One knows that tetravalence-doped La0.7Ce0.3MnO3 (LEMO) systems exhibit metal-insulator transition and ferromagnetic behavior, similar to the ditravalence-doped La0.7Ca0.3 MnO3. However, for the conductive mechanism of LEMO, strong controversies have existed for a long time with whether it is intrinsically electron-type or hole-type. Our experiments give evidence of the hole-type nature in LEMO. In the device with LEMO as channel and LaAlO3(LAO) as gate, applied positive bias poles gate and induces charge at the area between gate and channel. The polarized charge in the gate is compensated by inducing electrons in the channel. If LEMO is of electron-type, the increased carrier density would cause a decease of channel resistance. However, we experimentally found the channel resistance remarkably increases upon a positive bias. Such a fact is completely the same as the behavior observed in hole-doped La 0.7Ca0.3MnO3channel, and thus strongly supports the hole-type nature in LEMO channel. Furthermore, we found that the large field effect in LEMO is nonlinear and polarity dependent on the applied bias. A percolative phase separation picture is taking into account to interpret the observed field effect

Electrostatic modification of novel materials

Application of the field-effect transistor principle to novel materials to achieve electrostatic doping is a relatively new research area. It may provide the opportunity to bring about modifications of the electronic and magnetic properties of materials through controlled and reversible changes of the carrier concentration without modifying the level of disorder, as occurs when chemical composition is altered. As well as providing a basis for new devices, electrostatic doping can in principle serve as a tool for studying quantum critical behavior, by permitting the ground state of a system to be tuned in a controlled fashion. In this paper progress in electrostatic doping of a number of materials systems is reviewed. These include structures containing complex oxides, such as cuprate superconductors and colossal magnetoresistive compounds, organic semiconductors, in the form of both single crystals and thin films, inorganic layered compounds, single molecules, and magnetic semiconductors. Recent progress in the field is discussed, including enabling experiments and technologies, open scientific issues and challenges, and future research opportunities. For many of the materials considered, some of the results can be anticipated by combining knowledge of macroscopic or bulk properties and the understanding of the field-effect configuration developed during the course of the evolution of conventional microelectronics. However, because electrostatic doping is an interfacial phenomenon, which is largely an unexplored field, real progress will depend on the development of a better understanding of lattice distortion and charge transfer at interfaces in these systems.

The influence of static-electric field on the transport properties in La0.7Ca0.3MnO3 epitaxial thin films

We investigated the effect of static-electric field on the transport properties in La0.7Ca0.3MnO3 (LCMO) epitaxial thin films using a field effect configuration (FEC). A single layer LCMO film with thickness about 100nm was grown on LaAlO3 (LAO) substrate by pulsed laser deposition technique. A simple FEC was then formed on it using lithography technique, in which the LCMO film was used as channel, and LAO substrate as gate. Such a simple configuration is much easier to fabricate compared to the previously reported multilayer FEC. The transport behaviors of the LCMO channel for electric field bias ranging from +80to−80V were studied. Field effect is found to be significant. The maximum of electroresistance (ER) reaches 32%. An important feature is that the ER changes sign with the field direction, but the temperature TP, at which the resistance peaks, keeps nearly unchanged upon any bias. The films could return to their pristine state completely after the bias was removed, and the ER effect can be fully reproducible. However, we found a critical bias exists for these films. When the applied bias reaches +170V, the system could not revert to its initial state, instead a high resistive peak appears at low temperature. The appeared resistive peak behaves sensitively to small currents. A weak current could remarkably depress the resistance. The observed phenomena are discussed in the framework of phase separation mechanism.

Investigations on electroresistance effect in epitaxial manganite films using field effect configurations

The influence of static electric field on the transport properties in La0.7A0.3MnO3 (A=Ca,Ba) epitaxial thin films was investigated by using field effect configurations (FEC). A single layer manganite film was deposited on LaAlO3 (LAO) substrate by pulsed laser deposition technique, and then a simple FEC was formed on it using the lithography technique, in which the manganite film was used as a channel, and the LAO substrate as a gate. Surprising results were achieved by employing such a FEC. The transport resistance increases with a positive gate voltage but decreases with a negative bias, which means the electroresistance (ER) effect changes sign with the field direction. The observed reduction of resistivity for the La0.7Ca0.3MnO3 and La0.7Ba0.3MnO3 channels reaches ∼32% and ∼34% upon a bias of −80 and −300V, respectively. The films could completely return to their pristine state after the bias was removed and the ER effect could be fully reproduced.

Electroresistance and electronic phase separation in mixed-valent manganites.

The sensitivity of transport in colossal magnetoresistance (CMR) manganites to external electric and magnetic fields is examined using field effect configurations with La(0.7)Ca(0.3)MnO(3) (LCMO), Na(0.7)Sr(0.3)MnO(3), La(0.7)Ba(0.3)MnO(3), and La(0.5)Ca(0.5)MnO(3) (0.5-doped LCMO) channels, and ferroelectric PbZr(0.2)Ti(0.8)O(3) (PZT) or dielectric (SrTiO(3)) gates. A large electroresistance (ER) of approximately 76% at 4 x 10(5) V/cm is found in LCMO with PZT-ferroelectric gate, but the magnitude of the effect is much smaller (a few percent) in the other three channels. The ER and CMR effects are remarkably complimentary. The size and systematics of the effect strongly favor a percolative phase separation picture.

Field-effect-induced metastable conductivity changes in n-type a-Si:H

A lightly doped n-type a-Si:H film, arranged in a field effect configuration, has been subjected to bias-annealing treatments. Depending on the sign and the magnitude of the gate bias, the conductivity of the quenched-in metastable states could be varied throughout the entire range that is accessible by chemical doping. CPM-measurements performed on extreme states suggest that the conductance changes are controlled by field-induced changes in the donor density.

Distortion of Liquid Crystals in the Twisted Field Effect Configuration

Abstract The Freedericksz transition electric field induced distortion of nematic liquid crystals is investigated for the case of the twisted field effect configuration. Experimental capacitance measurements agree well with numerical calculations which allows a reliable determination of the twist elastic constant.

Analysis of modulation spectra of stratified media

A general formulation is obtained which relates the relative change of reflectance observed in a normal-incidence modulated-reflectance experiment to the dielectric properties of the system for laminar configurations consisting of a substrate, ambient, and possible surface dielectric overlayers. The two general types of modulation interactions, perturbation-induced changes of the substrate dielectric function or of the thickness of one of the dielectric layers, are discussed as limiting cases. The modulated-substrate expressions are evaluated numerically for the case of optically thick Ni and Ni–Al203 films on a Ge substrate, typical examples of Schottky-barrier and MOS electroreflectance configurations. It is shown in the latter case that the intrinsic sensitivity obtainable with shot-noise-limited measurement systems is neither enhanced nor impaired for modulation measurements performed in the vicinity of the reflectance minima characteristic of these field-effect configurations, although operation near these minima should be avoided for other reasons. The line-shape evolution observed in reflectance measurements of the exciton polariton is shown to follow naturally from the interference effect of the small dielectric discontinuity within the sample. The approximate integral expression describing the effect of inhomogeneous perturbations is also related to the more-general laminar solution. It is shown that, for small modulations, the integral formulation is equivalent to treating the substrate as being uniform with respect to propagation, but producing a net reflected component of the field, obtained by summing the values at the surface of the reflected components generated at the small dielectric discontinuities between the hypothetical laminations in the limit that the lamination thickness approaches zero.