Zero Bias Research Articles

Zero‐bias elimination with selective non‐commensurate sampling for PN code tracking

Zero bias is the main source of error in high-precision applications based on pseudo-noise (PN) ranging. This study proposes a selective non-commensurate sampling frequency design method applied to the digital code-tracking loop which can effectively suppress the code-phase zero bias caused by incomplete sampling of the spread spectrum signal. The maximum (MAX) and standard deviation (STD) of the zero bias independent of code and the initial phase are used to design the sampling frequency. The code correlation reference waveform is utilised to establish a statistical analysis model of the digital discriminator zero bias. Analytical expressions of the zero-bias MAX and STD are derived. The performance of the proposed method is assessed as per code Doppler, binary offset modulation, and thermal noise. Fibre optic time synchronisation equipment is used to determine the feasibility of eliminating PN code-tracking zero bias based on selective non-commensurate sampling.

Andreev reflection in nodal-line Weyl semimetal

Based on the Bogoliubov-de Gennes equation, the quantum scattering problem through a nodal-line Weyl semimetal based normal metal/superconductor heterojunction has been theoretically studied. Since the crystallographic anisotropy in the material, two different orientations between the crystalline axis and the superconducting interface have been revealed. Considering a heterojunction with the interface paralleling to the basal plane, it is found that Andreev reflection with due to Klein-like scattering gives rise to a perfect scattering. Deviation from the critical value, Andreev reflection falls down and normal reflection goes up. While the interface is perpendicular to the basal plane, the pure intra-mode retro-Andreev reflection (RAR) and inter-mode specular Andreev reflection (SAR) are manifested at the normal incident. Moreover, the reflection coefficient exhibits the reentrant behavior with the Fermi energy. Fundamentally, such features are a consequence of the torus-like iso-energy surfaces of the nodal-line Weyl semimetals, which is in sharp contrast to the case of conventional materials, graphene, and Weyl-point semimetals. Those novel scattering processes also result in a distinctive tunneling conductance, such as the sub-gap nonmonotonic features, the interface directional dependent zero bias conductances and the reentrant behavior, which can be served as a smoking gun to distinguish the mode-resolved Andreev reflections in experiments.

Analysis of current–voltage and capacitance–voltage characteristics of Zr/p-Si Schottky diode with high series resistance

Zr/p-Si Schottky diode was fabricated by DC magnetic sputtering of Zr on p-Si. Zr rectifying contact gave a zero bias barrier height of 0.73 eV and an ideality factor of 1.33 by current–voltage measurement. The experimental zero bias barrier height was higher than the value predicted by metal-induced gap states (MIGSs) and electronegativity theory. The forward bias current was limited by high series resistance. The series resistance value of 9840 [Formula: see text] was determined from Cheung functions. High value of the series resistance was ascribed to low quality ohmic contact. In addition to Cheung functions, important contact parameters such as barrier height and series resistance were calculated by using modified Norde method. Re-evaluation of modified Norde functions was realized in the direction of the method proposed by Lien et al. [IEEE Trans. Electron Devices 31 (1984) 1502]. From the method, the series resistance and ideality factor values were found to be as 41.49 [Formula: see text] and 2.08, respectively. The capacitance–voltage characteristics of the diode were measured as a function of frequency. For a wide range of applied frequency, the contact parameters calculated from [Formula: see text]–[Formula: see text] curves did not exhibit frequency dependence. The barrier height value of 0.71 eV which was in close agreement with the value of zero bias barrier height was calculated from [Formula: see text]–[Formula: see text] plot at 1 MHz. The values of acceptor concentration obtained from [Formula: see text]–[Formula: see text] curves showed consistency with actual acceptor concentration of p-Si.

Zero Bias Electron Transport Properties of Molecular Junctions Formed from Smallest Fullerenes C20 and C24

Zero Bias Electron Transport Properties of Molecular Junctions Formed from Smallest Fullerenes C20 and C24

Comparison of Microstrip W-Band Detectors Based on Zero Bias Schottky-Diodes

This paper presents and discusses three different low-cost microstrip implementations of Schottky-diode detectors in W Band, based on the use of the Zero Bias Diode (ZBD) from VDI (Virginia Diodes, Charlottesville, VA, USA). Designs are based on a previous work of modeling of the ZBD diode. Designs also feature low-cost, easy-to-use tooling substrates (RT Duroid 5880, 5 mils thickness) and even low-cost discrete SMD components such as SOTA resistances (State Of The Art TM miniaturized surface mount resistors), which are modeled to be used well above commercial frequency margins. Intensive use of 3D EM simulation tools such as HFSS TM is done to support microstrip board modeling. Measurements of the three designs fabricated are compared to simulations and discussed.

Wireless Power Transfer Using Rectenna

Radio frequency (RF) harvesting technologies are bewitching a huge number of people as they are enormously available in the atmosphere. These energies are received and converted to useful DC energy which can be used to charge electrical devices which need low power consumption. Here, in this paper a microstrip square patch antenna operating at 2.45 GHz is proposed having a dimension of 29.2mm × 29.2mm, which is fabricated on a low-cost FR4 substrate having a dielectric constant of 4.4 with a thickness of about 1.2 mm. L-shaped matching network is designed for maximum power transfer between the antenna and the rectifier. HSMS-2850 zero bias Schottky diode is used as a rectifier. The RF-DC rectification is done with an efficiency of 42.8% at -7dBm at 2.45 GHz.

Transconductance as a probe of nonlocality of Majorana fermions

Each end of a Kitaev chain in topological phase hosts a Majorana fermion. Zero bias conductance peak is an evidence of Majorana fermion when the two Majorana fermions are decoupled. These two Majorana fermions are separated in space and this nonlocal aspect can be probed when the two are coupled. Crossed Andreev reflection is the evidence of the nonlocality of Majorana fermions. Nonlocality of Majorana fermions has been proposed to be probed by noise measurements since simple conductance measurements cannot probe it due to the almost cancellation of currents from electron tunneling and crossed Andreev reflection. Kitaev ladders on the other hand host subgap Andreev states which can be used to control the relative currents due to crossed Andreev reflection and electron tunneling. We propose to employ Kitaev ladder in series with Kitaev chain and show that the transconductance in this setup can be used as a probe of nonlocality of Majorana fermions by enhancing crossed Andreev reflection over electron tunneling.

Photoelectrochemical Supercontinuum Solar Light Zero Bias Hydrogen Generation with Membrane-Based Cells Designed for Decreasing Overall Water Electrolysis Voltage and Water Dissociation (23)

We have created a two-compartment cell (2CC) separated by a bipolar membrane (BPM1) sandwiched between through-holed electrodes (THEs) assembly (BPMTHEA-2CC) based on the Golden Role for sustainable water splitting derived from water dissociation (WD) with a dual chemical bias (CB).2 The BPMTHEA-2CC has distinguishing characteristics of integrated functionality of dualities, providing an infinite supply of active reaction species, H+ and OH-, from water with an opposite bidirectional charge separation under appropriate applied voltage conditions. We wish to suggest the feasibility of electrochemical water splitting (decomposition) with less than theoretical 1.23 V at RT using an anolyte (water or base)|OER active THE|BPM|HER active THE|catholyte (water or acid). We disprove the theory of water electrolysis established for hundreds of years with sustainable dual CBs. However, we still require external voltage for water electrolysis. Instead of external voltage, we have harnessed solar energy by applying the TH n-type semiconductor photoanodes to BPMTHEA-2CC for a zero-bias photogalvanic cell. Anatase TH TiO2 was used for a model to demonstrate our concept. We succeeded in measuring photocurrent from distilled water with a response of optical shutter. The magnitude of the zero bias photocurrent is proportional to the magnitude of outer CB and illuminance intensity. TH Fe2O3 was prepared by the aqueous chemical growth method. Visible light zero bias photocurrent from distilled water was also observed in the TH Fe2O3 photogalvanic cell without any external voltage. Currently, our research efforts are focused on PEC zero bias hydrogen generation with harnessing supercontinuum solar light by designing optical tandem, wavelength multiplexing with BPMTHEA-2CC and Au plasmon-induced WD. 1) V. J. Frilette, J. Phys. Chem., 60, 435 (1956).2) K. Sakamaki et al., 97th CSJ, 3A6-05 (2017), 68th ISE, Providence, USA, ise171503 (2017), The 22nd Top. Meeting of ISE, Tokyo, abs170627 (2018), 69th ISE, Bologna, Italy, ise183543 (2018). Figure 1

Giant Zero Bias Anomaly due to Coherent Scattering from Frozen Phonon Disorder in Quantum Point Contacts.

We demonstrate an unusual manifestation of coherent scattering for electron waves in mesoscopic quantum point contacts, in which fast electron dynamics allows the phonon system to serve as a quasistatic source of disorder. The low-temperature conductance of these devices exhibits a giant (≫2e^{2}/h) zero bias anomaly (ZBA), the features of which are reproduced in a nonequilibrium model for coherent scattering from the "frozen" phonon disorder. According to this model, the ZBA is understood to result from the insitu electrical manipulation of the phonon disorder, a mechanism that could open up a pathway to the on-demand control of coherent scattering in the solid state.

A study of high piezomagnetic (Fe-Ga/Fe-Ni) multilayers for magnetoelectric device

This paper sets out the research into (Fe-Ga/Fe-Ni)n films in order to obtain a large piezomagnetic coefficients of 8.1 ppm/Oe and enhance magnetoelectric coupling at near zero bias field. The exchange coupling between Fe-Ga and Fe-Ni magnetic film makes the magnetoelectric (ME) coefficient of (8 nm Fe-Ga/8 nm Fe-Ni)30/AlN/Mo/Si reach 607 V/cm Oe, and the bias magnetic field is reduced to 4 Oe. Multilayer (8 nm Fe-Ga/8 nm Fe-Ni)30 films also have good soft magnetic properties, high piezomagnetic coefficients and low losses which can be used as a driving element for micro-sensor and micro-electro-mechanical system (MEMS).

Anomalous zero bias conductance peaks in a graphene-based ferromagnet/insulator/p-wave superconductor hybrid structure

We theoretically study graphene-based ferromagnet/insulator/p-wave superconductor hybrid structure, where an anomalous zero bias conductance peak (ZBCP) is exhibited. With the exchange field h increased, the zero-bias conductance dips (ZBCDs) for both the px- and py-wave situations develop into ZBCPs at h∕EF>1, which are just contrary to the situation at h∕EF<1. Furthermore, with the enhancement of barrier strength χ, the conversion from the ZBCD to ZBCP is displayed in the region of h∕EF>1 for the px-wave, whereas the sharp ZBCP remains all the time at any h for the py-wave. More interestingly, the zero-bias conductance for the px-wave keeps unchanged upon increasing χ, while for the py-wave, exhibits periodical modulation of χ. The singular features can be used to not only identify the p-wave superconductivity and spin polarization in graphene but also pave the way to a new class of tunable superconducting spintronic devices based on large-scale graphene.

Anomalous zero bias conductance peak in a ferromagnetic graphene junction with d-wave anisotropic superconducting pair symmetry

We theoretically present an anomalous zero bias conductance peak (ZBCP) in graphene junctions with proximity-induced ferromagnetism and d-wave anisotropic superconducting pair symmetry (ASPS) herein. It is revealed that in the thin insulator limit, the ZBCP can be periodically recovered by adjusting the sandwiched insulating barrier strength χ regardless of exchange field h and the phase of the periodical behaviours for h larger than its Fermi energy EF (h &amp;gt; EF) is exactly opposite to that for h &amp;lt; EF. Most interestingly, in the context of h &amp;gt; EF, the periodic oscillation of the nonzero bias conductance located in the ZBCP versus χ, is accompanied by an explicit splitting peak. Moreover, under the situation of the insulator with finite width, the conductance exhibits a stronger damping oscillation with bias voltage eV for any h, which is also accompanied by a splitting ZBCP at h &amp;gt; EF. These singular features originate from ferromagnetic-modulated midgap states characteristic by the relativistic nodal fermions, which confirms the spin polarization and ASPS of the graphene, and thus will be of great interest in the designing and fabrication of graphene superconducting spintronic devices.

Zero bias anomaly in the two-site Anderson-Hubbard model with Gaussian distribution for disorder

The Anderson-Hubbard model considers the correlation between disorder and other interactions in a strongly correlated electron system. Both disorder and correlations drive the metal-insulator transition but the densities of states behave in different ways. The zero bias anomaly (ZBA) referring to the V-dip shape of the density of states at the Fermi energy occurs in the strong disorder and strong interaction regime instead of a hard Coulomb gap in an insulator phase of strongly correlated interacting systems. In this paper, we use a Gaussian distribution for disorder to examine a two-site Anderson-Hubbard model. We also explain comprehensively the relationship between the phase diagram of ground states with various numbers of electrons and the behavior of the density of states. Furthermore, we want to investigate the effect of disorder distribution on the formation of the ZBA which originates from a hopping mechanism in two specific configurations.

Zero bias UV detection and precursor effect on properties of ZnO nanorods grown by hydrothermal method on SiO2/p-Si substrate

Here we present the effect of the precursor chemistry on the properties of ZnO nanorods prepared by using the hydrothermal method. The nanorods were grown over RF-sputtered 50 nm ZnO seed layers on integrated circuits compatible highly lattice mismatched SiO2/p-Si substrates. Two zinc sources namely zinc acetate and zinc nitrate were dissolved in solvent (a solution of deionized water and hexamethylenetetramine) in parallel to grow the highly conducting, vertically-aligned ZnO nanorods. Surface morphology and crystal structure of NRs were investigated using scanning electron microscope and X-ray diffraction. Nanorods synthesized in zinc acetate precursor's solution were highly crystalline and sparsely packed with well defined hexagonal top surface compared to nanorods grown in zinc nitrate precursors. Elemental composition of nanorods was studied using X-ray photoelectron spectroscopy. The oxygen and zinc observed in all the nanorods, zinc acetate synthesized nanorods show high atomic percentage of these two elements. To test the electrical and photo detection properties of the ZnO nanorods a metal semiconductor metal (MSM) structure was fabricated by depositing Ti/Au ohmic contacts over the nanorods. The MSM structure fabricated over the nanorods synthesized by using zinc nitrate precursor shows zero bias UV detection not reported up to present. The conducting properties of the nanorods were obtained from the current-voltage characteristics measurements of the MSM photosensor, and it is observed that the zinc acetate synthesized NRs were highly conducting. The UV detection capability of the MSM photosensor were tested by exposing UV light from light emitting diodes of same power and different wavelength. The ZnO NRs grown in zinc nitrate precursor shows high photosensitivity.

Zero bias emission current in laser heated emissive probe and proper choice of probe-tip material

Emissive probes are considered as one of the best diagnostic tools for the direct measurement of plasma potential in low temperature plasma systems. Laser-heated emissive probes (LHEPs), due to their higher lifetime, are becoming more popular than their current-heated conventional counterparts. Graphite due to its higher absorption coefficient at CO2 laser wavelength and LaB6 due to its lower work function are commonly used as the probe materials for laser heated probes. Experiments with a probe-tip made of a graphite material have revealed that the emission processes other than thermionic emission also occur on heating the material with the laser, which can affect the plasma potential measurements and change the I-V characteristics of the LHEP. This additional emission due to the laser irradiation on the graphite-tip explains the measurements of lower values of plasma potentials and also describes the observation of an increase in electron saturation current with the increase in thermionic emission current due to heating. The possible mechanisms of this negatively charged-emission other than the thermionic emission from the graphite-tip have been thoroughly characterized in the absence of plasma. This extra emission is not observed in the probe-tip made up of LaB6, and a good comparison of I-V characteristics could be established with a conventional filament emissive probe in the case of LaB6.

Finite bias evolution of bosonic insulating phase and zero bias conductance in boron-doped diamond: A charge-Kondo effect

We report novel transport features in heavily boron-doped nanocrystalline diamond films, in particular an anomalous resistance peak near to the superconducting transition temperature and a strong zero bias conductance peak in the differential current-voltage spectra. The shape of the resistance-temperature curves near the critical temperature is seen to be strongly influenced by both magnetic field and bias current. As the bias current is lowered, the resistance peak becomes more pronounced, whereas when the magnetic field is varied the peak shifts towards lower temperatures. The resistance upturn shows a quadratic temperature dependence as expected for a Kondo transition. We find that a number of transport features such as resistance peak height, zero bias conduction peak height and width scale according to a power law dependence. We interpret these features as a result of a charge-Kondo effect where hole dopants act as degenerate Kondo impurities by opening additional pseudo-spin scattering channels.

Measuring Thermally-Driven LED Emissions via Voltage Modulation near Zero Bias

This study was launched to demonstrate that LEDs at zero bias show recombination photon emissions, and to check the models for the same. A method for measuring the light emission for a LED near zero bias is presented. A large reverse bias sufficient to suppress detectable emissions is assumed. The bias voltage between ‘large reverse’ and our target voltage is modulated, and the difference measured. The measured emissions found are consistent with the Shockley diode equation. The spectrum near zero bias can be measured and characterized. It shows LED behavior that is substantially different from other typical measurements, and suggests a violation of Kirchhoff’s Law.

Efficiency enhancement for microcrystalline silicon solar cells by a lens-like structure to maintain improved photocarriers distribution

Spatial distribution of the photogenerated carriers in a hydrogenated microcrystalline silicon (μc-Si : H) solar cell has a significant impact on its electrical characteristics. Photogeneration distribution can be manipulated using photon management techniques. The electrical specifications of a typical thin-film μc-Si : H solar cell under various distributions of photocarriers are thoroughly investigated for both zero and higher bias voltages. For a thin-film μc-Si : H solar cell with a typically low thickness, we conclude that a photogeneration distribution having a greater rate in the central region of the solar cell performs optimally. This result is in contrast to the previously reported results in the literature for some other thin-film solar cell technologies, where the improved performance of a thin-film solar cell is believed to be when the photogenerated carriers are concentrated near the anode. It is demonstrated that the dominant contribution of dark carriers to recombination in the middle of the cell at higher bias voltages causes this effect. Moreover, we propose a lens-like structure by patterning top layers of a μc-Si : H solar cell, which approximately realizes the desired photogeneration distribution and provides an increase in the density of photocarriers in the middle of the solar cell, while it also acts as an antireflection coating. This proposed configuration has a 1.3% improvement in power conversion efficiency compared with a planar μc-Si : H solar cell with identical constituting layers and similar dimensions.

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

We study the effect of external electric fields on superconductor-semiconductor coupling by measuring the electron transport in InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor. We find that the gate voltage induced electric fields can greatly modify the coupling strength, which has consequences for the proximity induced superconducting gap, effective g-factor, and spin–orbit coupling, which all play a key role in understanding Majorana physics. We further show that level repulsion due to spin–orbit coupling in a finite size system can lead to seemingly stable zero bias conductance peaks, which mimic the behavior of Majorana zero modes. Our results improve the understanding of realistic Majorana nanowire systems.

Enhancement of broadband ultraviolet visible photodetection by boron nitride nanoparticles in bulk graphene oxide layer

A proposed boron nitride/graphene oxide (BN/GO) composite photodetector (PD) was prepared using a drop cast method for photodetection in the ultraviolet (UV) and visible light ranges. Morphology of the GO, distribution of BN nanoparticles and composition of B, N, C and O elements were confirmed by field emission scanning electron microscope (FESEM) analysis and energy dispersive x-ray (EDX) spectroscopy results. Raman scattering indicates high frequency intrinsic E2g vibrations at 1349 cm−1 and low intense peaks at 803 cm−1 from hexagonal BN (h-BN) structures in the bulk GO layer, while an overlap in the D and G bands at 1349 and 1581 cm−1 respectively indicates the presence of the GO layer. Excellent photoconduction of 380 and 405 nm UV sources and a 650 nm red laser source showed that the measured photocurrent is dependent on power regardless of the signal wavelength. Variations in sensitivity allow the device to be operated at selected direct current (DC) bias voltages, while high frequency modulation at 1000 Hz showed a profound rise and fall time about 13.6 and 245.6 μs respectively. Characteristics as self-powered PD was observed, has an enhancement about 3450% at its zero bias voltage.