Potential Barrier Structure Research Articles

Transmittance on combinatorial structures of triple potential barriers

Semiconductor materials used as potential barriers in the study are GaAs, GaSb, and AlAs. These materials will be arranged in certain combinations to form triple potential barrier structures and the effect of combinations will be analysed against transmission coefficient values. In this study, the maximum energy of the electron is 1 eV and the matrix propagation method is used where the effect of the combinations structure on transmission coefficient values is numerically analysed using a computational program. The results showed that the structuring potential barrier affects the value of the transmission coefficient. In the uniform barriers arrangements, the value of the transmission coefficient decreases with increasing potential barrier energy. Whereas in the arrangement of different barrier combinations, two opposing combination arrangements have the same transmission coefficient values. Thus, from six combination arrangements, there are three kinds of transmission coefficient values. The maximum transmission coefficient value is 1.000 in the triple potential barrier of GaSb at 0.49 eV. Research on the tunnel effect contributed to the development of electronic and optoelectronic devices such as transistors and lasers.

Excellent detection of H2S gas at ppb concentrations using ZnFe2O4 nanofibers loaded with reduced graphene oxide

Cost-effective fabrication of sensors and detection of ultralow concentrations of toxic gases are important concerns for environmental monitoring. In this study, the reduced graphene oxide (RGO)-loaded ZnFe2O4 nanofibers (ZFO-NFs) were fabricated by facile on-chip electrospinning method and subsequent heat treatment. The multi-porous NFs with single-phase cubic spinel structure and typical spider-net morphology were directly assembled on Pt-interdigitated electrodes. The diameters of the RGO-loaded ZFO-NFs were approximately 50–100 nm with many nanograins. The responses to H2S gas showed a bell-shaped behaviour with respect to RGO contents and annealing temperatures. The optimal values of the RGO contents and the annealing temperatures were found to be about 1.0 wt% and 600 °C, respectively. The response of the RGO-loaded ZnFe2O4 NFs to 1 ppm H2S gas was as high as 147 at 350°C while their cross-gas responses to SO2 (10 ppm), NH3 (100 ppm), H2 (250 ppm), C3H6O (1000 ppm), and C2H5OH (1000 ppm) were rather low (1.8−5.6). The high sensor response was attributed to formation of a heterojunction between RGO and ZnFe2O4 and due to the fact that NFs consisted of many nanograins which resulted in multi-porous structure and formation of potential barriers at grain boundaries.

Confining Dirac electrons on a topological insulator surface using potentials and a magnetic field

We study the effects of extended and localized potentials and a magnetic field on the Dirac electrons residing at the surface of a three-dimensional topological insulator like ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$. We use a lattice model to numerically study the various states; we show how the potentials can be chosen in a way which effectively avoids the problem of fermion doubling on a lattice. We show that extended potentials of different shapes can give rise to states which propagate freely along the potential but decay exponentially away from it. For an infinitely long potential barrier, the dispersion and spin structure of these states are unusual and these can be varied continuously by changing the barrier strength. In the presence of a magnetic field applied perpendicular to the surface, these states become separated from the gapless surface states by a gap, thereby giving rise to a quasi-one-dimensional system. Similarly, a magnetic field along with a localized potential can give rise to exponentially localized states which are separated from the surface states by a gap and thereby form a zero-dimensional system. Finally, we show that a long barrier and an impurity potential can produce bound states which are localized at the impurity, and an ``L''-shaped potential can have both bound states at the corner of the L and extended states which travel along the arms of the potential. Our work opens the way to constructing wave guides for Dirac electrons.

Potential barrier and band structure of closed edge graphene

The atomic structure, electron distribution, work function, and band structure of closed edge graphene are investigated with density functional theory. Field emission performance of closed edge graphene is compared with that of open edge graphene. We provide a possible explanation for the field emission microscopy image change after high emission current, which appeals to the experimentalists for further investigation.

Disorder effects on electronic bandgap and transport in graphene-nanomesh-based structures

Using atomistic quantum simulation based on a tight binding model, we investigate the formation of electronic bandgap Eg of graphene nanomesh (GNM) lattices and the transport characteristics of GNM-based electronic devices (single potential barrier structure and p-n junction) including the atomic edge disorder of holes. We find that the sensitivity of Eg to the lattice symmetry (i.e., the lattice orientation and the hole shape) is significantly suppressed in the presence of disorder. In the case of strong disorder, the dependence of Eg on the neck width fits well with the scaling rule observed in experiments [Liang et al., Nano Lett. 10, 2454 (2010)]. Considering the transport characteristics of GNM-based structures, we demonstrate that the use of finite GNM sections in the devices can efficiently improve their electrical performance (i.e., high ON/OFF current ratio, good current saturation, and negative differential conductance behaviors). Additionally, if the length of GNM sections is suitably chosen, the detrimental effects of disorder on transport can be avoided to a large extent. Our study provides a good explanation of the available experimental data on GNM energy gap and should be helpful for further investigations of GNM-based devices.

Calculation of Temperature Coefficient of Resistance for Potential Barrier Structure for Bolometer in Uncooled Infrared Image Sensor

Calculation of Temperature Coefficient of Resistance for Potential Barrier Structure for Bolometer in Uncooled Infrared Image Sensor

Calculation of Temperature Coefficient of Resistance for Potential Barrier Structure for Bolometer in Uncooled Infrared Image Sensor

A potential barrier structure is a candidate for producing high temperature coefficient of resistance (TCR) devices. The electrical characteristics of such a structure for application in a bolometer for an infrared image sensor are calculated on the basis of a thermionic electron emission theory and the effect of tunneling through the barrier layer. The TCR is obtained using the resistivity dependence on temperature and depends mainly on the barrier height. The TCR value is derived as a function of the barrier height, barrier thickness, and bias voltage to the structure. To obtain a TCR of greater than 0.04/K, the barrier height must be more than 0.3 eV. The resistivity also depends on barrier height. The thickness of the barrier layer is also important because it affects the resistivity and TCR. Proper design of a potential barrier structure will yield a bolometer film having a high TCR and low resistivity.

Reaction between graphene and hydrogen under oblique injection

The reaction between a graphene sheet and an incident hydrogen atom was clarified through a classical molecular dynamics simulation based on the modified Brenner’s reactive empirical bond order potential under the NVE condition, in which the number of particles (N), volume (V), and total energy (E) are conserved. The energy dependence of three types of reaction (i.e., adsorption, reflection, and penetration) for the oblique injection of a hydrogen atom into a graphene sheet was investigated. The reaction depends on the energy and two angular parameters, namely, the polar angle θ and the azimuthal angle φ of the incident hydrogen atom. The reflection and adsorption rates were found to strongly depend on θ. This dependence is caused by the three-dimensional structure of small potential barriers that cover adsorption sites (i.e., a local minimum point of the potential energy). The θ dependence of the penetration rates was observed. The penetration rates are proportional to cos2θ. The φ dependence of the penetration rates was also observed when θ is large.

Structure of vortex shedding past potential barriers moving in a Bose-Einstein condensate

The problem of excitation of a homogeneous Bose-Einstein condensate by axially symmetric potential barriers moving with respect to the condensate with both supersonic and subsonic velocities is considered in terms of the Gross-Pitaevskii equation. The specific features of the structure of the vortex shedding past the barriers are analyzed for both regimes of motion.

Structural features at the potential barrier

A new model of the potential-barrier structure of emitter is proposed. The effect of such a fine structure on the current characteristics is demonstrated for thermionic and field emission. The existence of a critical transition for the Schottky correction is proposed.

Magnetoresistance oscillations in magnetic tunnel junction

We report unconventional oscillatory tunnel magnetoresistance as a function of applied bias in the magnetic tunnel junction with the Al 2O 3 barrier. We attribute this feature to the inhomogeneity of the potential barrier structure. Ferromagnetic grains inside the potential barrier are formed at the technological stage. In this case, the TMR oscillation occurs due to the discrete charging effect that is well known as the Coulomb blockade.

Enhanced solid-state thermionic emission in nonplanar heterostructures

Conservation of transverse momentum during thermionic emission from planar structures is a key factor limiting the number of hot electrons emitted and the efficiency of solid-state thermionic energy conversion devices. In this letter, electron emission from nonplanar potential barrier structures is analyzed using a Monte Carlo transport model. Compared to the planar structures, nonplanar tall barriers can achieve much larger emission currents. Although the average energy of the transmitted electrons drops a little, the thermoelectric figure of merit can be increased with a nonplanar barrier structure. The improvement of the thermoelectric properties is attributed to the combined effects of increased effective interface area and reduced probability of total internal reflection at heterostructure interfaces.

Analytical formula of the transmission probabilities across arbitrary potential barriers

The analytical transfer matrix method is applied to the evaluation of the tunnelling in the semiconductor heterostructures. An analytical formula of the transmission probabilities across arbitrary shaped potential barriers which includes the variations of the effective masses has been developed in this paper. Various potential barrier structures are analysed and the results are of high precision. Tunnelling resonance is obtained for the double-barrier structure. We can correlate the energy location of the peaks of the transmission probability with the bound state energies of the included potential wells through our analytical transfer matrix method.

A Novel Contactless Method for Characterization ofSemiconductors: Surface Electron Beam Induced Voltage in Scanning Electron Microscopy

We present a novel contactless and nondestructive method called thesurface electron beam induced voltage (SEBIV) method for characterizingsemiconductor materials and devices. The SEBIV method is based on thedetection of the surface potential induced by electron beams of scanningelectron microscopy (SEM). The core part of the SEBIV detection set-upis a circular metal detector placed above the sample surface.The capacitance between the circular detector and whole surface of the sampleis estimated to be about 0.64 pf. It is large enough for the detectionof the induced surface potential. The irradiation mode of electron beam(e-beam) influences the signal generation. When the e-beam irradiateson the surface of semiconductors continuously, a differential signal isobtained. The real distribution of surface potentials can be obtainedwhen a pulsed e-beam with a fixed frequency is used for irradiation anda lock-in amplifier is employed for detection. The polarity of inducedpotential depends on the structure of potential barriers and surfacestates of samples. The contrast of SEBIV images in SEM changes withirradiation time and e-beam intensity.

Materials issues for layered tunnel barrier structures

Layered dielectric tunnel barriers are expected to greatly increase the program/erase speeds of nonvolatile floating gate memory devices and could allow both nanosecond program/erase times as well as archival data storage. We have correlated dielectric constants and band offsets with respect to silicon in order to help identify possible materials from which to construct these devices. A numerical model has been developed to assess potential layered tunnel barrier materials and structures suitable for integration into silicon electronics. With this model, we explore the relative dominance of Fowler–Nordheim tunneling and thermionic emission and we present simulated I–V curves for some candidate materials.

Thin film microstructure and thermal transport simulation using 3D-films

Simulations of the flow of heat through porous thin films by the three-dimensional microstructural thin film simulation framework 3D-Films are discussed in this paper. For each simulation, the film structures are generated by the thin film growth model 3D-Films and then used to generate a finite difference based thermal model by the program 3D-Films/Thermal. This program creates a block based data structure using a 3D quadtree mesh and subsequently solves for the steady state heat flow through the film structure. In this paper the film growth and thermal models are used to analyze and suggest optimization of porous thermal barrier coatings produced by glancing angle deposition techniques. The paper also deals with the determination of the accuracy and efficiency of the thermal model. Studies on the effect of reducing the resolution of the simulated film for less memory intensive thermal simulations are presented, indicating that a reduction of the resolution by a factor of 3 and the number of solution variables by as much as a factor of 27 is feasible. The simulations Of ZrO 2 thermal barriers are compared to experimental results with a relatively close match being obtained. Finally, the simulator is used to analyze the effectiveness of a number of potential thermal barrier structures produced by glancing angle deposition techniques. These results suggest that the most effective thermal barrier film microstructures will be porous films consisting of slanted posts or large pitch helices.

Tunnelling coefficients across an arbitrary potential barrier

A simple, yet accurate, method of solving the Schrodinger equation across an arbitrary potential barrier is described, based on the analytic transfer-matrix technique. This paper gives the final analytical expression for the transmission probability. Numerical calculations for four typical potential barrier structures are compared with the traditional WKB, modified WKB and the modified Airy function (MAF) methods. Excellent agreement with an exact example is demonstrated. Most importantly, in cases where other potential-barrier methods fail, our method performs well.

Far-infrared induced current in a ballistic channel–potential barrier structure

We consider electron transport in a ballistic multi-mode channel structure in the presence of a transversely polarized far-infrared (FIR) field. The channel structure consists of a long resonance region connected to an adiabatic widening with a potential barrier at the end. At frequencies that match the mode energy separation in the resonance region we find distinct peaks in the photocurrent, caused by Rabi oscillations in the mode population. For an experimental situation in which the width of the channel is tunable via gates, we propose a method for reconstructing the spectrum of propagating modes, without having to use a tunable FIR source. With this method the change in the spectrum as the gate voltage is varied can be monitored.

Observation of Resonant Photon Tunneling in Photonic Double Barrier Structures

Reflectance and transmittance of 632.8 nm He-Ne laser light for photonic double barrier structures (consisting of a SF10 prism, SiO2 layer, Al or Al2O3 active layer, SiO2 layer and SF10 prism) were measured as a function of the angle of incidence for both the ρ- and s-polarized incidence. Sharp reflection dips and transmission peaks were observed at angles larger than the critical angle of total reflection. The appearance of the transmission peaks can be attributed to resonant photon tunneling through the photonic double barrier structures analogous to resonant electron tunneling through double potential barrier structures. Resonant tunneling is mediated by the long-range surface plasmon polariton in the case of the Al active layer and the electromagnetic guided modes in the case of the Al2O3 layer.

Analysis of resonant tunneling using the equivalent transmission-line model

Presents a simple general and exact method for solving resonant tunneling problems in multilayered heterostructures. This method is based on the analogy of wave propagation between the transmission line and the potential structure. By using the proposed method, it is shown that electron wave propagation can be treated as wave propagation on an equivalent circuit and that various problems can be systematically solved by using well-developed circuit functions and circuit matrixes. In particular, our equivalent circuit can be effectively used for analysis of resonant interband tunneling (RIT) structures and resonant tunneling structures including /spl Gamma/-X mixing by using the interface matrix. Various properties of the resonant tunneling structure and a guideline for designing new quantum effect devices can be easily obtained. In order to show the validity and usefulness of this method, some numerical examples of InAs-GaSb and GaAs-AlAs potential barrier structures are presented.