Potential Barrier Height Research Articles

Measurement and analysis of the height of potential barrier and depth of moving potential dot in the quantum point contact

Employing the measure of I (Vds) characteristics (current versus bias voltage) at fixed gate voltages, the height of potential barrier in the quantized acoustoelectric (AE) current plateau region was estimated and analyzed. The results show that the height of the electrostatic potential of gate voltage in the first quantized AE plateau was in the range from 216 to 222 meV, while that was about 200 meV in the second quantized AE plateau. And the conversion efficiency of the gate voltage is approximately 0.67 meV/mV, which is higher than the data (0.3 meV/mV) of the device designed by split gate technique. The positions of minimum depth of moving potential dots are ωt=0.78π and 1.22π in a SAW cycle, and the lowest depth in the first quantized AE current plateau is about 6.5 meV, while the lowest depth is 12.6 meV in the second quantized AE current plateau.

Optimized dual-function varistor-capacitor ceramics of core-shell structured xBi2/3Cu3Ti4O12/(1-x)CaCu3Ti4O12 composites

xBi2/3Cu3Ti4O12/(1-x)CaCu3Ti4O12 composites were prepared by traditional solid-state reaction method. Extremely high nonlinear coefficient of 25 and breakdown field of 18.92 kV·cm−1 were obtained in small current range of 0.1−1 mA·cm-2. In addition, reduced dielectric loss of 0.055 was achieved with high dielectric constant of 1369. Optimized nonlinear and dielectric properties were integrated to make the composites a promising dual-function varistor-capacitor candidate. Microstructure analysis discovered two areas with various Bi/Ca ratio, designated as Bi-H and Bi-L respectively. It was found that the maximum ratio of Bi-H/Bi-L heterogeneous interface corresponded to optimized nonlinear and dielectric performance, which was associated with elevated potential barrier height and huge grain boundary resistance. Combined with relaxation analysis, a core-shell structure was proposed to elaborate microstructure evolution in xBi2/3Cu3Ti4O12/(1-x)CaCu3Ti4O12 composite. According to the core-shell model, variation of heterogeneous interface was illustrated on how to influence nonlinear properties, which was well fitted to experimental results.

Influence of spark plasma sintering temperature on the microstructures, dielectric and I–V properties of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) ceramics were prepared by the sol–gel process and sintered by the spark plasma sintering (SPS) process at different temperatures. The SPS process temperature has an important effect on the microtopography of CCTO ceramics. The results of EDS and positron annihilation spectroscopy indicate that Cu2+ diffuses from the inside to the surface of grains during the sintering process at high temperature. The permittivity (εr) of CCTO ceramics at the corresponding frequencies increases with increasing SPS temperature. However, the frequency stability of εr over the frequency range 40–106 Hz wanes gradually. The CCTO ceramics sintered at 900°Cand 950 °C present very low dielectric loss values(about 0.02) near 10 kHz. The change in εr and tanδ for CCTO ceramics can be explained by the internal barrier layer capacitance (IBLC) model and AC (alternating current) impedance spectra. The results of I–V nonlinear characteristics for CCTO ceramics make clear that the potential barrier height has a positive effect on the value of nonlinear coefficient.

NovelWoods–Saxon stochastic resonance system for weak signal detection**Project supported by the National Natural Science Foundation of China (Grant No. 61501525) and the National Natural Science Foundation of Hunan Province of China (Grant No. 2018JJ3680).

We propose a joint exponential function and Woods–Saxon stochastic resonance (EWSSR) model. Because change of a single parameter in the classical stochastic resonance model may cause a great change in the shape of the potential function, it is difficult to obtain the optimal output signal-to-noise ratio by adjusting one parameter. In the novel system, the influence of different parameters on the shape of the potential function has its own emphasis, making it easier for us to adjust the shape of the potential function. The system can obtain different widths of the potential well or barrier height by adjusting one of these parameters, so that the system can match different types of input signals adaptively. By adjusting the system parameters, the potential function model can be transformed between the bistable model and the monostable model. The potential function of EWSSR has richer shapes and geometric characteristics. The effects of parameters, such as the height of the barrier and the width of the potential well, on SNR are studied, and a set of relatively optimal parameters are determined. Moreover, the EWSSR model is compared with other classical stochastic resonance models. Numerical experiments show that the proposed EWSSR model has higher SNR and better noise immunity than other classical stochastic resonance models. Simultaneously, the EWSSR model is applied to the detection of actual bearing fault signals, and the detection effect is also superior to other models.

Performance deterioration of GaN-based laser diode by V-pits in the upper waveguide layer

Abstract The effect of V-pits in the upper waveguide (UWG) on device performance of GaN-based laser diodes (LDs) has been studied. Experimental results demonstrate that in comparison with the LDs with u-In0.017Ga0.983N/u-GaN multiple UWG or u-In0.017Ga0.983N one, the LDs with a single u-GaN UWG has the best device performance. They have a smaller threshold current density, and a larger and more stable output optical power. The lowest threshold current density is as low as 1.3 kA/cm2, and the optical power reaches to 2.77 W. Furthermore, atomic force microscopy suggests that the deterioration of device performance of former kinds of devices may be attributed to the increase of V-pits’ size and quantity in the undoped-In0.017Ga0.983N UWG layer, and these V-pits could introduce more nonradiative recombination centers and exacerbate the inhomogeneity of injection current. Moreover, theoretical calculation results indicate that the increase of leakage current and optical loss are additional reasons for the device performance deterioration, which may be caused by a reduction of the potential barrier height for electrons in the quantum wells and by an increased background electron concentration in UWG.

Mechanically tuned conductivity at individual grain boundaries in polycrystalline ZnO varistor ceramics

Mechanically induced changes in electrical properties have gained increasing interest over the last decade. The research field piezotronics, which describes the change in potential barrier height (e.g., at Schottky contacts) by piezoelectric charges, could lead to promising applications such as sensors or strain trigged transistors. In this contribution, the changes of potential barriers by mechanical stress at several grain boundaries of polycrystalline ZnO have been quantified. Rationalization is provided by concurrent measurement of crystal orientations of both neighboring grains. The highest changes in barrier height could be observed at ZnO–ZnO grain boundaries exhibiting varistor properties. In this case, the barrier height can be almost completely reduced by positive piezoelectric charges. Furthermore, an increase in barrier height is observed with negative piezoelectric charges. The developed physical model suggests an equivalent impact of externally applied voltage and induced positive piezoelectric charge on the barrier properties. In turn, not only the barrier height is modified by piezoelectric charges but also the breakdown voltage. This has, nevertheless, been only indirectly verified in experiments. These allow rationalizing the proposed model. Furthermore, a statistical study reveals a change in the distribution of breakdown voltages with changing stress conditions in the varistor ceramic.

Impact of the dangling bond defects and grain boundaries on trapping recombination process in polycrystalline 3C SiC

The bulk polycrystalline (pc) 3C SiC of n- and p-type obtained by thermal decomposition of methyltrichlorosilane vapor have been studied by applying the electron paramagnetic resonance (EPR), direct current (DC) conductivity, photoconductivity (PC) and PC time-resolved decay methods. The energy level of the two donor-like minority carrier traps at ε1 = 77 meV and ε2 = 92.6 meV located at the grain boundaries (GB) of pc-3C SiC has been obtained using the measurements of the temperature dependence of DC conductivity and PC in the range of 80–600 K. The minority carrier traps assigned to carbon and silicon dangling bonds with the carbon back bonds were observed in the EPR spectra of pc-3C SiC of n- and p-type at g = 2.0029(3), g = 20042(3), respectively. The PC time decay after the termination of the photo-excitation was studied in monocrystalline and pc-3C SiC of n- and p-type at 80 K. The persistent relaxation of PC has been described by kinetic equations accounting the trapping, ionization, and recombination processes of non-equilibrium charge carriers bound dynamically to shallow donors and acceptors. We have concluded that the main process responsible for the long-lived relaxation of the PC is trap-assisted electron-hole recombination in n-type pc-3C SiC and ionization of boron acceptors, as well as the hole escape/capture at the boron level in p-type pc-3C SiC. The differences in the relaxation process of the PC in n- and p-type pc-3C SiC were explained by the presence of the potential barrier height of about 8.6 meV at GB for the capture of the majority carriers in p-type pc-3C SiC.

Effect of a barrier defect in the creation of localized states in the structure of multi-quantum wells

Our work is based on the study of a multi-quantum well (MQW) GaAs/AlxGa1-xAs containing a defect barrier Ga1-xAlxAs of a thickness d02 (cavity). The potential barrier height and the effective mass are determined by the Al concentration. We have found modes inside the gaps; these modes are localized in the 3d gaps, so they are considered as localized states, which are largely dependent on the defect parameters. Their transmissions, variation of the energy versus the defect barrier thickness and their quality factor, have been studied. We found that the modes depend also on the parameters of the structure. Their quality factor increases, when the defect thickness increases too. Therefore, it is possible to conclude that both the position, the thickness of the defect barrier, can play an essential role in the creation of localized states.

Investigating the effect of the conductivity of the electron transportation layer on the organic light-emitting diodes

In this paper, we choose three types of n-doped electron transport layer (ETL) materials with different chemical structures to fabricate only-electron carrier device for studying the conductivity of them, namely, 100 nm ETL1, 40 nm ETL2, and 23 nm ETL3. It is also analyzed that the effect of the potential barrier height on the carrier injection efficiency of the single-carrier device when they directly contact with the electrode having the different work function ITO (indium tin oxide film) electrode. When the thickness of the organic electron transport layer is thin, the current density is mainly limited by the injection barrier in the interface, However, When the thickness of the organic electron transport layer is thick, the organic electron transport layer with very low carrier mobility is a dominant factor in limiting the current through the device. If ETL1 is in contact with a lower work function aluminum electrode relative to the ITO electrode, the effect of the injection limit on the current is weaker. Considering Poole-Frenkel effect and space charge limited current effect, the field strength-dependent carrier mobility of ETL1 material is estimated by linear-fitting the current-electric field characteristic curve of only-electron device. Organic red light-emitting diode is fabricated with ETL1 thicknesses of 10 nm and 100 nm, respectively. For the organic light-emitting device with 100 nm ETL1, it reaches 14.9 cd/A at a current density of 30 mA/cm2 , and the color coordinates is (0.658, 0.341).

Electro-opto-mechano driven reversible multi-state memory devices based on photocurrent in Bi0.9Eu0.1FeO3/La0.67Sr0.33MnO3/PMN-PT heterostructures.

A single device with extensive new functionality is highly attractive for the increasing demands for complex and multifunctional optoelectronics. Multi-field coupling has been drawing considerable attention because it leads to materials that can be simultaneously operated under several external stimuli (e.g. magnetic field, electric field, electric current, light, strain, etc.), which allows each unit to store multiple bits of information and thus enhance the memory density. In this work, we report an electro–opto–mechano-driven reversible multi-state memory device based on photocurrent in Bi0.9Eu0.1FeO3 (BEFO)/La0.67Sr0.33MnO3 (LSMO)/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) heterostructures. It is found that the short-circuit current density (Jsc) can be switched by the variation of the potential barrier height and depletion region width at the Pt/BEFO interface modulated by light illumination, external strain, and ferroelectric polarization reversal. This work opens up pathways toward the emergence of novel device design features with dynamic control for developing high-performance electric–optical–mechanism integrated devices based on the BiFeO3-based heterostructures.

Temperature-dependent heterojunction device characteristics of n-ZnO nanorods/p-Si assembly

Heterojunction diode based on n-ZnO nanorods/p-Silicon (Si) assembly was fabricated, examined and reported here. Horizontal quartz tube thermal evaporation technique was used for the growth of ZnO nanorods on Si substrate. The nanorods were characterized by several techniques to examine the structural, morphological, scattering and electrical properties. Wurtzite hexagonal phase of the grown aligned nanorods was observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The appearance of a sharp Raman peak at 438 cm–1 was observed and it is related to the E2(high) mode of the wurtzite hexagonal phase of ZnO. The electrical properties of the fabricated heterojunction assembly were examined at different temperatures (298∼398 K) in both reverse and forward biased conditions, and a good stability was observed over the entire temperature range. A reduction in the turn-on and breakdown voltage was observed with increasing temperature. By increasing the temperature, the effective potential barrier height was increased, while quality factor was decreased. The observed activation energy was found to be ∼93.4 meV, higher than the exciton binding energy of ZnO.

Влияние усиленной электрическим полем термической электронной эмиссии на температуру катода с тонкой диэлектрической пленкой в дуговом газовом разряде

A model of thermal electron emission enhanced by the electric field (thermo-field emission) from the metal cathode substrate into a thin insulating film formed on its surface is developed. A system of equations for the cathode surface temperature in the arc discharge and the electric field strength in the film, providing the required discharge current density, is formulated. It is shown that existence of the dielectric film can result in a considerable reduction of the cathode temperature in the discharge due to lower potential barrier height at the metal-insulator boundary than at the metal-discharge boundary in case of the metal cathode without the film. It is found that due to an enhancement of thermal emission of electrons into the film by the electric field generated in it, an additional decrease of the cathode temperature by about 100 K takes place.

A 4H-SiC UV Phototransistor With Excellent Optical Gain Based on Controlled Potential Barrier

In this article, we report the experimental results of a visible-light-blind 4H-polytype silicon carbide phototransistor able to detect ultraviolet (UV) radiations for wavelengths lower than 380 nm with a significative improvement in the optical gain compared with the state-of-the-art of 4H-SiC UV phototransistors. From the electro-optical measurements, the device shows a dark current of 0.62 pA, an ON-/OFF-current ratio of seven orders of magnitude up to bias voltage of −0.5 V, and an excellent optical gain of $1.14\cdot {10}^{{{5}}}$ at 300 nm, whereas it is only $2.6\cdot {10}^{-{{3}}}$ at 400 nm demonstrating a good rejection of visible radiations. Besides having high optical gain, the phototransistor is also more sensitive than the conventional 4H-SiC UV detectors for wavelengths with low penetration depths, because its structure is designed to have the electric field up to the radiated surface where the photogenerated electron–hole pairs are efficiently swept up before recombination occurs. The operating principle of the detector is also investigated, and we experimentally proved that differently from the conventional 4H-SiC bipolar junction transistor phototransistor, it is based on the change in the potential barrier height, which controls the current flow, due to the variation in the Fermi levels when the electron–hole pairs are photogenerated. A comparison with the state-of-the-art of 4H-SiC UV phototransistors is reported.

Polarity dependent DC resistance degradation and electrical breakdown in Nb doped PZT films

The role of interfacial defect chemistry in time dependent breakdown and associated charge transport mechanisms was investigated for Pb0.99(Zr0.52Ti0.48)0.98Nb0.02O3 (PNZT) films. Electrical degradation was strongly dependent on the sign of the electric field; a significant increase in the median time to failure from 4.8 ± 0.7 to 7.6 ± 0.4 h was observed when the top electrode was biased negatively compared to the bottom electrode. The improvement in the electrical reliability of Pt/PNZT/Pt films is attributed to (1) a VO•• distribution across the film due to PbO nonstoichiometry and (2) Ti/Zr segregation in PNZT films. Compositional mapping indicates that PbO loss is more severe near the bottom electrode, leading to a VO•• gradient across the film thickness. Upon degradation, VO•• migration toward the bottom Pt electrode is enhanced. The concentration of VO•• accumulated near the bottom Pt interface (6.2 × 1018/cm3) after degradation under an electric field of 350 kV/cm for 12 h was two times higher than that near the top Pt/PNZT interface (3.8 × 1018/cm3). The VO•• accumulation near the bottom Pt/PNZT interface causes severe band bending and a decrease in potential barrier height, which in turn accelerates the electron injection, followed by electron trapping by Ti4+. This causes a dramatic increase in the leakage current upon degradation. In contrast to the bottom Pt/PNZT interface, only a small decrease in potential barrier height for electron injection was observed at the top Pt/PNZT interface following degradation. It is also possible that a Zr-rich layer near the top interface reduces electron trapping by Ti4+.

Valley-dependent electron retroreflection and anomalous Klein tunneling in an 8- Pmmn borophene-based n−p−n junction

We investigate the transport properties in an 8-$Pmmn$ borophene-based $n\text{\ensuremath{-}}p\text{\ensuremath{-}}n$ junction. The valley-dependent electron retroreflection is generated by changing the direction of junction, which breaks up the conventional wisdom that only the electron specular reflection occurs at an interface. Furthermore, the valley-dependent anomalous Klein tunneling, i.e., the perfect transmission at a nonzero incident angle of electron regardless of the width and height of potential barrier, is found. Interestingly, this anomalous Klein tunneling depends on the direction of junction and the tilted velocity. These two findings arise from the same fact that the anisotropic band structure, induced by tilted and anisotropic velocities, leads to the release of locking relation between the transverse wave vector and velocity component along the interface. Our work gives insight into the understanding of the electron retroreflection and the Klein tunneling.

Giant dielectric behavior of monovalent cation/anion (Li+, F−) co‐doped CaCu3Ti4O12 ceramics

AbstractGiant dielectric behavior and electrical properties of monovalent cation/anion (Li+, F−) co‐doped CaCu3Ti4O12 ceramics prepared by a solid‐state reaction route were systematically investigated. Substitution of Li+ and F− led to a significantly enlarged mean grain size. A reduced loss tangent (tanδ ~0.06) with the retainment of an ultra‐high dielectric permittivity (ε′ ~7.7‐8.8 × 104) was achieved in the co‐doped ceramics, while the breakdown electric field and nonlinear coefficient of CaCu3Ti4O12 ceramics were increased by co‐doping with (Li+, F−). The variations in nonlinear electrical properties and giant dielectric response, as well as the dielectric relaxation, were well explained by the Maxwell‐Wagner polarization model for an electrically heterogeneous microstructure, in which a Schottky barrier height at the grain boundaries (GBs) was formed. ε′ was closely correlated to the GB capacitance. Significantly decreased tanδ value and enhanced nonlinear properties were related to a significant increase in the GB resistance, which was attributed to the significantly increased potential barrier height and conduction activation energy at the GBs. The semiconducting nature of the grains was also studied using X‐ray photoelectron spectroscopy and found to originate from the presence of Cu+ and Ti3+ ions.

High-performance PTCR ceramics with extremely low resistivity for multilayer chip thermistor application

It is a great challenge to prepare chip thermistors with high positive temperature coefficient of resistivity (PTCR) jump and simultaneously low room temperature resistivity by reduction-reoxidation method. In this work, the influence of Mn doping on Ba0.996La0.004(Bi0.5Na0.5)0.003TiO3 based chip thermistors were carefully investigated and Mn doping was proved to be an effective way in preparation of high-performance PTCR ceramics with low resistivity. The results showed that Mn can't create a high enough potential barrier in un-oxidized samples but can obviously increase the value of potential barrier height after reoxidation. The trap activation of Mn d states near Curie point helps to reduce room temperature resistivity and increase PTCR jump in reoxidized samples. As a result, samples with extremely low resistivity and high PTCR jump of 103.4 were reported for the first time.

Quantum diffusion regime of charge transport in GdB6 caused by electron and lattice instability

Based on accurate X-ray structure analysis of GdB6 over the temperature range 85-300 K it has been shown that anomalously strong charge carrier scattering in the quantum diffusion regime of charge transport in this compound arises due to the formation of (i) dynamically coupled Gd3+ dimers of about 3.3 {\AA} in size with an energy of quasi-local oscillations ~ 7 - 8 meV and (ii) dynamic charge stripes along the [001] direction of the cubic lattice. It has been revealed that anharmonic approximation is useful when analyzing the static and dynamic components of the atomic displacement parameters of gadolinium. The barrier height of double-well potential of Gd3+ ions was determined both from low-temperature heat capacity measurements and from the electron density distribution reconstructed from X-ray data.

Analytic modeling of breakdown voltage shift in the CMOS buried multiple junction detector

We propose an analytical model for the CMOS Buried Multiple Junction (BMJ) detector exhibiting breakdown voltage shift depending on adjacent junction’s bias. The device’s singular behavior has been observed when two adjacent junctions are in reach-through (RT) condition. The breakdown current has been identified to be predominated by thermionic emission. The proposed model determines, for a given BMJ structure with uniform or Gaussian doping distributions under bias conditions, whether two adjacent junctions are in RT condition. In this case, it calculates the merged depletion limits, electric field and electrostatic potential profile. The potential barrier height of each merged depletion region can then be extracted and the thermionic current be computed.Model computations have been compared with TCAD simulations and measurements on the BMJ detector. Good agreements have been observed for different structures in different bias conditions at different temperatures.

A Two Dimensional Tunneling Resistance Transmission Line Model for Nanoscale Parallel Electrical Contacts

Contact resistance and current crowding are important to nanoscale electrical contacts. In this paper, we present a self-consistent model to characterize partially overlapped parallel contacts with varying specific contact resistivity along the contact length. For parallel tunneling contacts formed between contacting members separated by a thin insulating gap, we examine the local voltage-dependent variation of potential barrier height and tunneling current along the contact length, by solving the lumped circuit transmission line model (TLM) equations coupled with the tunneling current self consistently. The current and voltage distribution along the parallel tunneling contacts and their overall contact resistance are analyzed in detail, for various input voltage, electrical contact dimension, and material properties (i.e. work function, sheet resistance of the contact members, and permittivity of the insulating layer). It is found the existing one-dimensional (1D) tunneling junction models become less reliable when the tunneling layer thickness becomes smaller or the applied voltage becomes larger. In these regimes, the proposed self-consistent model may provide a more accurate evaluation of the parallel tunneling contacts. For the special case of constant ohmic specific contact resistivity along the contact length, our theory has been spot-checked with finite element method (FEM) based numerical simulations. This work provides insights on the design, and potential engineering, of nanoscale electrical contacts with controlled current distribution and contact resistance via engineered spatially varying contact layer properties and geometry.