Two-terminal Structures Research Articles

Study of optical, electrical and magnetic properties of composite nanomaterials on the basis of broadband oxide semiconductors

Vertically oriented arrays of zinc oxide nanorods with high structural perfection and good optical properties have been obtained by gas-phase synthesis from the elements on the substrates. Homogeneous and heterogeneous e-n transitions have been produced on the basis of these arrays of nanorods. Thermal growth from salt mixtures has been used to synthesize zinc oxide nanorods doped with transition metals (Fe, Mn, Cr). Zinc oxide nanorods doped with iron, manganese, tin, and lithium showed room-temperature ferromagnetic properties. Two-terminal planar structures have been produced from the nanorods doped with chrome. These structures are sensitive to ultraviolet radiation and insensitive to visible light. The field-effect transistor made from the zinc oxide nanorod doped with chrome has electron conductivity and works in the enhancement mode.

Admittance Measurements on OFET Channel and Its Modeling With <formula formulatype="inline"><tex>$R$</tex></formula>–<formula formulatype="inline"><tex>$C$</tex></formula> Network

For the modeling of charge response behavior in the organic field-effect-transistor (OFET) channel, the admittance of the OFET channel is measured from the two-terminal MIS structures. The channel is considered as an R-C network, and both the capacitance and loss of the measured admittance show good agreement with the model. The effective delay of the R-C network depends on the sheet resistance of the channel, the insulator capacitance, and the channel length. The maximum operating frequency of an OFET can be limited by this delay, because the channel charges cannot be induced completely within the delay time

Electrical properties of thin nanocrystalline diamond based structures

Electrical structures based on thin films of nanocrystalline diamond are described as well as their electrical properties. Diamond films with thickness between 0.25 and 1.0 μm and with average grain sizes of 300 nm and less are formed by microwave plasma-assisted chemical vapor deposition. Electrical properties of free-standing diamond films and of substrate mounted films are measured over a wide range of voltages with two-terminal electrical contacts. The films exhibited field-activated conductivity consistent with a Poole–Frenkel reduction in ionization energy associated with overlapping Coulombic potentials, well-modeled by Poole's Law. Metallization was performed on diamond films supported on the original silicon substrate and also on free-standing diamond. For the latter, the silicon substrate was removed by back-etching and the diamond film was transferred to a different structure. Both symmetrical and asymmetrical current–voltage characteristics have been obtained. Depending on the type of contacts, the rectification ratios of two-terminal structures range from 1 to 11,000 at high applied voltages.

Channel Width Dependence of Spin Polarized Transports in NiFe/InGaAs Hybrid Two-Terminal Structures

We investigated spin polarized transports in NiFe/InGaAs hybrid two-terminal structures at 1.5K as well as their channel width dependence. The two-terminal structures were fabricated in order to neglect the local Hall effect (LHE) by fringe fields of NiFe contacts. First, we measured magneto-resistance (MR) characteristics of the samples under vertical magnetic fields, and obtained clear oscillations indicating the ohmic formation at NiFe/InGaAs interfaces. Next, we measured spin valve (SV) properties under parallel magnetic fields, and successfully observed clear SV peaks without LHE hysterisis loops. Furthermore, we also confirmed unique behavior of SV peaks depending on the channel width. Such dependence also indicates spin injection/detection through NiFe/InGaAs interfaces.

Symmetry of Spin Transport in Two-Terminal Waveguides with a Spin-Orbital Interaction and Magnetic Field Modulations

We analyze symmetries of spin transport in two-terminal quantum waveguide structures with Rashba spin-orbit coupling and magnetic field modulations. Constraints, imposed by the device structure, on the spin polarization of the transmitted electron beam from the waveguide devices are derived. The results are expected to provide accuracy tests for experimental measurements and numerical calculations, as well as guidelines for spin-based device designs.

Field regulation of single-molecule conductivity by a charged surface atom

Electrical transport through molecules has been much studied since it was proposed that individual molecules might behave like basic electronic devices, and intriguing single-molecule electronic effects have been demonstrated. But because transport properties are sensitive to structural variations on the atomic scale, further progress calls for detailed knowledge of how the functional properties of molecules depend on structural features. The characterization of two-terminal structures has become increasingly robust and reproducible, and for some systems detailed structural characterization of molecules on electrodes or insulators is available. Here we present scanning tunnelling microscopy observations and classical electrostatic and quantum mechanical modelling results that show that the electrostatic field emanating from a fixed point charge regulates the conductivity of nearby substrate-bound molecules. We find that the onset of molecular conduction is shifted by changing the charge state of a silicon surface atom, or by varying the spatial relationship between the molecule and that charged centre. Because the shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature.

High-Frequency Solid-State Electronic Devices

Starting with exploratory work in the 1930s and development work in the 1940s a variety of two-terminal and three-terminal solid-state device structures have been proposed, fabricated, and developed. This work parallels the development effort on vacuum electronic devices, and the two technologies share many applications. The solid-state and vacuum electronic devices work in tandem to enable numerous commercial and military systems. Solid-state device development is closely linked to semiconductor materials growth and processing technology, and advances such as the introduction of heterojunction growth technology, permit complex multiple layer device structures to be fabricated and optimized for maximized device performance. This work has been very successful and a variety of high-performance diodes and transistors are now available for use from UHF into the millimeter-wave spectrum, approaching terahertz frequencies. The development, operating principles, and state-of-the-art of various diode and transistor structures are reviewed.

Mortality Dependence of Cu Dual Damascene Interconnects on Adjacent Segment

AbstractThree terminal ‘dotted-I’ interconnect structures, with vias at both ends and an additional via in the middle, were tested under a variety of test conditions. Failures (mortalities) were observed even when segments were tested under conditions that would not have led to failure in two-terminal structures. Mortalities were found in right segments with jL values as low as 1250 A/cm, which is lower when compared to the immortality condition (jL)cr of 3700 A/cm reported for similar via-terminated structures. Moreover, we found that the mortality of a dotted-I segment is dependent on the direction and magnitude of the current in the adjacent segment. These results suggest that there is not a definite value of the jL product that defines true immortality in individual segments that are part of an interconnect tree. More importantly, the critical jL value for a single segment of Cu interconnects may be reduced or increased by an adjacent segment. Therefore independently determined (jL)cr values cannot be directly applied to interconnects with branched segments, but rather the magnitude as well as the direction of the current flow in the adjoining segments must be taken into consideration in evaluating the immortality of interconnect segments in an interconnect network.

Photoinduced relaxation effects in three-terminal polymer based device structures

We examine the dynamics of relaxation of the excess current generated by photoexcitation in different structures. The excess current is introduced upon photoexciting the devices for a certain duration. The decay process of this current in polymer field effect transistors (FETs) upon switching off the excitation source can be appropriately modeled to a serial relaxation dynamics arising from a hierarchy of systems with increasing spatial separation of the photo-generated negative and positive charges. The results at different gate voltages are informative in terms of extracting the spatial distribution of the trapped carriers. These results are compared to decay rates in two-terminal planar structures and Schottky barrier modified two-terminal planar structures.

Effects of breaking current conservation on the phase properties of two-terminal quantum systems

We study the reflection and transmission phase properties of two-terminal quantum structures coupled to a third lead. The systems are effectively three-terminal and current conservation is broken with regard to the original two-terminal systems. Two structures, a waveguide with an attached stub quantum dot and a waveguide with an inline, double-barrier confined quantum dot, are considered. The transmission and reflection phase properties are calculated for these systems with different couplings to the third lead. The results show that the discontinuous phase shifts seen in the current-conserved two-terminal systems are removed when the third lead is attached. However, as long as the coupling between the quantum systems and the additional lead is weak, sharp but continuous phase drops within narrow energy ranges can still be clearly identified.

Self-assembled monolayer organic field-effect transistors.

The use of individual molecules as functional electronic devices was proposed in 1974 (ref. 1). Since then, advances in the field of nanotechnology have led to the fabrication of various molecule devices and devices based on monolayer arrays of molecules. Single molecule devices are expected to have interesting electronic properties, but devices based on an array of molecules are easier to fabricate and could potentially be more reliable. However, most of the previous work on array-based devices focused on two-terminal structures: demonstrating, for example, negative differential resistance, rectifiers, and re-configurable switching. It has also been proposed that diode switches containing only a few two-terminal molecules could be used to implement simple molecular electronic computer logic circuits. However, three-terminal devices, that is, transistors, could offer several advantages for logic operations compared to two-terminal switches, the most important of which is 'gain'-the ability to modulate the conductance. Here, we demonstrate gain for electronic transport perpendicular to a single molecular layer ( approximately 10-20 A) by using a third gate electrode. Our experiments with field-effect transistors based on self-assembled monolayers demonstrate conductance modulation of more than five orders of magnitude. In addition, inverter circuits have been prepared that show a gain as high as six. The fabrication of monolayer transistors and inverters might represent an important step towards molecular-scale electronics.

Langevin Forces and Generalized Transfer Fields for Noise Modelling in Deep Submicron Devices

We present a generalized transfer field method with the microscopic noise sources directly connected with the velocity and energy change during single scattering events. The advantages of this method are illustrated by hydrodynamic calculations of current and voltage noise spectra in several two-terminal submicron structures.

Thin-Film Electroluminescent Device Physics Modeling

Previous and current approaches to alternating current thin-film electroluminescent (ACTFEL) device physics modeling are reviewed. The primary goal of the modeling efforts of interest to this review is to accurately simulate the electrical properties of two-terminal ACTFEL test structures when subjected to realistic applied voltage waveforms. A comprehensive review of previous ACTFEL modeling efforts is presented. Additionally, two modeling methodologies that are believed to hold the most promise for accurate ACTFEL device modeling are presented. These methodologies involve state-space simulation of a discretized phosphor and SPICE simulation.

Transfer impedance calculations of electronic noise in two-terminal semiconductor structures

The time-domain formulation of the transfer-impedance method is developed to calculate the impedance field of two-terminal semiconductor structures. The voltage noise spectrum associated with velocity fluctuations is then calculated for overmicron and submicron n+nn+ GaAs diodes in the framework of a closed hydrodynamic approach based on the velocity and energy conservation equations. Transit-time effects are found to influence substantially the noise spectrum in a wide frequency range above 10 GHz. The good agreement found with Monte Carlo simulations validates the proposed theoretical approach.

Noise temperature of n+nn+ GaAs structures.

The noise temperature of GaAs ${\mathit{n}}^{+}$${\mathit{nn}}^{+}$ two-terminal structures of micrometer and submicrometer lengths is theoretically analyzed as a function of frequency and applied voltage. Calculations are performed at a kinetic level, and are based on a mixed Monte Carlo hydrodynamic scheme. Different operation modes of the structure are considered, namely, when operating as a nonlinear resistor (passive device) as well as when operating as a Gunn amplifier or generator (active device). Under generating conditions the noise temperature at low frequency is found to go to infinity for voltages above the threshold value for the Gunn effect, as expected in bulk material. Under amplifying conditions the noise temperature at low frequency is found to remain finite even at applied voltages well above the threshold value for the Gunn effect. At high frequencies the noise-temperature spectrum shows structures associated with transit-time effects, carrier energy, and plasma-time effects. In particular, we calculate the noise figure of merit covering both amplifying and passive conditions. Very good agreement is found between theory and available experiments. \textcopyright{} 1996 The American Physical Society.

Charge pumping and pseudopyroelectric effect in active ferroelectric relaxor-type films.

Unidirectional charge flow was observed in potassium tantalum niobate, ${\mathrm{KTa}}_{0.6}$${\mathrm{Nb}}_{0.4}$${\mathrm{O}}_{3}$, films. These films of relaxor-type diffuse phase transition material were formed by metalorganic deposition and had a polarization gradient normal to the surface of the films. Novel charge pumping was observed in the active operation of simple two-terminal structures by excitation with periodic, strong electric fields. Such operation also showed a large pseudopyroelectric response. Effective pyroelectric coefficients as large as 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ C/${\mathrm{cm}}^{2}$ \ifmmode^\circ\else\textdegree\fi{}C have been obtained.

Electrical characterization of p-type ZnSe:Li epilayers grown on p+-GaAs by molecular-beam epitaxy

Small-signal ac admittance data are presented, and shown to provide accurate and unambiguous evidence of p-type behavior in Li-doped ZnSe epilayers grown on p+-GaAs. The devices measured are two-terminal vertical-transport structures, with unequal-area contacts in order to distinguish effects arising from the top metal Schottky barrier from those arising from the heterojunction. Qualitative features of the data alone are sufficient to determine the (positive) sign of the mobile carriers in the ZnSe. The data are analyzed using an equivalent-circuit model shown to be reliable for n-type ZnSe, from which the net doping and the ZnSe resistivity are extracted. Using these quantities, the ZnSe hole mobility is found to be about 28±4 cm2/V s. Schottky barrier and heterojunction barrier heights are also determined.

EXPLOSIVE PROCESSING OF BULK SUPERCONDUCTORS

ABSTRACT This paper describes the explosive fabrication of novel, bulk superconducting composites and monolithic prototypes which serve to explore a range of applications including superconducting tapes, two-terminal linear bus structures for solid-state switching applications, and planar arrays for microwave antenna and magnetic shielding. The systems explored include copper and silver matrices encapsulating Yba2Cu3O7 superconducting powder and metal powder mixtures (Cu and Ag), Bi7Pb3Sr10Ca10Cu15O7 in copper, and Y-Ba-Cu-O and Bi-Pb-Sr-Ca-Cu-O in copper/silver/6061 -T6 aluminum alloy composites. The optimization of the powder consolidation and metal-matrix welding as well as shock-pressure induced alterations in residual superconductivity are examined by measuring bulk resistance versus temperature (R-T) and microwave surface resistances, relative susceptibilities, and relative levitation heights (as an indication of magnetic flux exclusion) with peak shock wave pressures which characterize the explosiv...

Electrical characteristics of Al/ZnS/ p− n+ Si diode structures for electroluminescent devices

Experimental steady-state current-voltage ( I- V) and capacitance-voltage ( C- V) characteristics of Al/ZnS/ p− n + Si two-terminal structures for d.c. electroluminescent devices are reported. The ZnS layers were deliberately undoped in order to study the electrical properties in the absence of luminescent radiation. Under the action of large depleting voltages, both the I- V and C- V data exhibit marked departures from the ZnS limited behaviour observed at lower voltages. The deviations result from the onset of appreciable electron flow through the ZnS above some critical applied voltage and take the form of pronounced “knee” or “step” like features for both types of data. Above the “knee” the device current is determined by the minority carrier supply from the Si substrate and the I- V curves “flatten-out.” A deep depletion mode ensues and the high-frequency device capacitance falls below its quasi-equilibrium minimum value. Estimates of the critical field for charge leakage through the ZnS lie in the region of ∼ 5 × 10 5 V cm −1 for the present devices. As reported previously, the current-limiting action of the Si depletion layer is a potentially useful feature for Si-based d.c. electroluminescent devices.

Optimal design of amorphous/crystalline tandem cells

Computer analysis has been used to determine the conversion efficiency of amorphous-on-crystalline and crystalline-on-amorphous two-cell tandem structures as a function of the energy gaps of the component cells. Four-terminal (separately connected) structures have higher efficiencies than two-terminal (series-connected) structures and are less sensitive to variations in energy gap, operating temperature and air mass. The optimal amorphous/crystalline tandem structures show only a modest increase in efficiency over their component crystalline cells. Unless the production costs of the tandem structures are low, this increase may not be sufficient to justify their adoption.