Schottky Barrier Formation Research Articles

Investigation of nano Ag-decorated SiC particles for photoelectrocatalytic dye degradation and bacterial inactivation

Spherical silver nanoparticles (Ag–NPs) were grown on near spherical β-SiC to assess the photocatalytic and antibacterial performance in the perspective of the future development of Ag decorated SiC porous membrane for next generation water treatment. A classic hierarchical structure of Ag on SiC (Ag@SiC) particles was developed in the presence of different percentage of 1, 3, and 5 wt% Ag. These were evaluated for the photocatalytic (PC) degradation behavior of organic dyes and E.coli under irradiation of UV-light. The optimum 3 wt% Ag-decorated β-SiC photocatalyst enhances the rate of dye degradation in the presence of external potential of 3 V. Schottky barrier formation in the interface between Ag@SiC improves the charge separation and consequently enhances the efficiency of the degradation process. Strong antimicrobial effect is observed at lower potential that can be attributed to effective charge transfer by metallic silver thereby suppressing the probable recombination through active separation. The catalyst were found stable and analyzed in the perspective of reuse and reproducibility. Thus, nano Ag (3 wt%) @β-SiC is a prospective material for water treatment.

Enhanced visible-light photocatalysis via back-electron transfer from palladium quantum dots to perylene diimide

The electronic-coupling interaction between noble-metal cocatalysts and host semiconductor nanocrystals has been found to be effective for the utilization of the solar energy. However, electron transfer (ET) mechanism between noble metals and self-assemblies has not been elucidated clearly. Here, we revealed a mechanism of back-electron-transfer-enhanced photocatalysis, which contributed to the visible-light photocatalytic improvement of perylene diimide (PDI) assembly for phenolic degradation and hydrogen generation. By compared with the energy level of PDI and Pd quantum dots (QDs), it seemed to be disadvantageous for ET from PDI assembly to Pd QDs, but surface photovoltage spectra showed that this can come true under visible-light irradiation, indicative of formation of a new Schottky barrier resulting from other light-induced transition species. Absorption spectra showed that an additional electronic state existed above the conduction band of PDI assembly originating from PDI radical anions. Such active species provided the light-driven dissipative structure with stable energy and electron flow through two opposite types of ET pathway: one is ET from light-excited PDI anions to Pd QDs and the other is direct electron injection from plasma Pd QDs accumulated with high-energy electrons to PDI neutral molecules. It has been found that continuous ET from PDI assembly to Pd QDs caused the plasma resonance of the Pd QDs to be higher in energy to overcome interfacial energy barrier. And then back-ET from Pd QDs to neutral PDI molecules occurred and led to formation of more PDI radical anions that were important for the improvement of the photocatalytic activity. These findings provide a new strategy for the development of highly efficient visible-light photocatalysts based on self-assembly for energy production.

Technological Fabrication Features of Microwave Device with Schottky Barriers

At present, research and development of heterojunctions are conducted in the directions of searching for new compositions and technological regimes for the creation of ohmic and barrier transitions for gallium arsenide. The transition to silver-based metallization, which has large thermal and electrical conductivity comparing with gold and a relatively low diffusion coefficient to gallium arsenide, should improve the technical characteristics of the devices. One of the most important technological operations in the formation of Schottky ohmic contacts and barriers is thermal annealing. Silver to gallium arsenide contacts are made in vacuum by the method of thermal evaporation. The deposition and thermal treatment regimes for creating ohmic contacts of Ag–Ge–In/ n–n + GaAs with specific contact resistance r c = (5...7)´10 –5 W×cm 2 are developed. The influence of the substrate temperature during the silver deposition and the annealing temperature on the height of the Schottky barrier Ag/ n–n + GaAs, the injection coefficient g and the nonideality factor h is established.

In-situ electronic conductivity measurements of LiNi0.45Mn1.485Cr0.05O4 thin films using all-solid-state thin-film batteries

Total electronic conductivity (σetotal) of LiNi0.45Mn1.485Cr0.05O4 thin film (LNM–Cr: 40nm in thickness) between 3.5 and 4.9V (vs. Li metal anode) was measured using all-solid-state thin-film battery (Li/LiPON/LPO/LNM–Cr) fabricated on interdigitated array (IDA) electrode. The LNM–Cr with disordered spinel phase was prepared by pulsed laser deposition on the IDA electrode. The σetotal depended on the voltage and reversibly changed regardless of lithium extraction/insertion process. Variation trends of the σetotal were in good agreement with the previous reports using the chemically delithiated powder materials. Grain boundary resistance contributes to the σetotal depending on the voltage probably because of the formation of double Schottky barrier at the grain boundaries.

Solution processed thin film transistor from liquid phase exfoliated MoS2 flakes

Two dimensional layers of dichalcogenide materials have attracted a lot of interests due to their potential applications in optoelectronics and energy storage. Hence, there is a large interest in establishing cheap, scalable processes for the production of low dimensional semiconducting dichalcogenide based films. In this work, well exfoliated MoS2 dispersions were prepared through a two-step liquid phase exfoliation process with N-methyl-pyrrolidone (NMP) and Isopropanol (IPA). The quality of the obtained MoS2 flakes was characterized by transmission electron microscopy, scanning electron microscopy, UV–Vis spectroscopy and Raman spectroscopy. For charge transport analysis, bottom-gate thin film transistors (TFTs) based on exfoliated MoS2 films were fabricated via spray coating technique. Electrical characterization of the obtained TFTs showed that adding a PMMA layer on top of the semiconductor lead to considerable improvements in the electrical performance. The analysis of the electrical characteristics suggests that the additional PMMA layer improves the charge transfer between adjacent flakes. Electrical measurements on TFTs with different channel length were used to separate the impact of the contact resistance and the channel resistance on the charge transport. The TFTs output curves showed non-linear current–voltage (I-V) characteristic. The non-linear behavior was attributed to the formation of Schottky barriers at the inter-flakes connection. In this work, we show a low-cost and scalable solution-based fabrication process that could boost the application of dichalcogenides in modern nanoelectronic devices.

Heterojunctions of mixed phase TiO2 nanotubes with Cu, CuPt, and Pt nanoparticles: interfacial band alignment and visible light photoelectrochemical activity

Anodically formed, vertically oriented, self-organized cylindrical TiO2 nanotube arrays composed of the anatase phase undergo an interesting morphological and phase transition upon flame annealing to square-shaped nanotubes composed of both anatase and rutile phases. This is the first report on heterojunctions consisting of metal nanoparticles (NPs) deposited on square-shaped TiO2 nanotube arrays (STNAs) with mixed rutile and anatase phase content. A simple photochemical deposition process was used to form Cu, CuPt, and Pt NPs on the STNAs, and an enhancement in the visible light photoelectrochemical water splitting performance for the NP-decorated STNAs was observed over the bare STNAs. Under narrow band illumination by visible photons at 410 nm and 505 nm, Cu NP-decorated STNAs performed the best, producing photocurrents 80% higher and 50 times higher than bare STNAs, respectively. Probing the energy level structure at the NP–STNA interface using ultraviolet photoelectron spectroscopy revealed Schottky barrier formation in the NP-decorated STNAs, which assists in separating the photogenerated charge carriers, as also confirmed by longer charge carrier lifetimes in NP-decorated STNAs. While all the NP-decorated STNAs showed enhanced visible light absorption compared to the bare STNAs, only the Cu NPs exhibited a clear plasmonic behavior with an extinction cross section that peaked at 550 nm.

Barrier characteristics and interface properties of Au/Ti/n-InAlAs Schottky contacts

The InAlAs surface morphology (AFM), chemical composition (XPS) and the Ti/InAlAs interface structure (HREM), during the Au/Ti/n-In0.52Al0.48As/InP(001) mesa-structure Schottky barrier formation, were studied. The current-voltage (I-V) dependences analysis of the formed Schottky barrier in the temperature range of 100–380K was carried out. It was shown that the I-V dependences are well described by the thermionic emission theory at temperatures above 200K with the ideality factor and the barrier height close to 1.09 and 0.7eV, respectively. At temperatures below 200K, the I-V behavior is attributed to the Schottky barrier anomalies, which are explained by the existence of nanometer-sized patches with a low barrier height having a Gaussian distribution (Tung model). According to this model, the temperature dependences of the barrier height and ideality factor were described with the following parameters: the homogeneous barrier height of 0.88eV and standard deviation of 10−4cm2/3V1/3. In the analysis of the modified Richardson plot, the Richardson constant (10.7Acm−2K−2) and the area fraction (24%), occupied by the patches with a low barrier height and diameter ~80nm, were calculated. The patches appearance is explained by the presence of the spikes detected on the InAlAs surface by the AFM method.

Impact of defect distribution on IrOx/ZnO interface doping and Schottky barriers

We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to measure the nature and spatial distribution of native point defects at Zn- and O-polar ZnO interfaces with iridium oxide (IrOx) and their impact on Schottky barrier formation. IrOx and other metal oxides exhibit higher Schottky barriers than their pure metal counterparts, consistent with wider depletion regions and potentially useful for ohmic contacts to p-type semiconductors. DRCLS with I-V and 1/C2-V barrier height and carrier profile measurements showed high zinc vacancy VZn and CuZn defect densities that compensate free carrier densities, increase depletion widths, and form higher effective barriers than Ir/ZnO contacts. Zn-polar versus O-polar ZnO interfaces with IrOx exhibit 40% higher VZn + CuZn interface segregation and lower carrier densities within a wider depletion region, accounting for the significantly higher (0.89 vs. 0.67 eV) barrier heights. Both the depth of VZn density segregation and the Zn-deficient layer thickness measured microscopically match the depletion width and applied electric fields comparable to spontaneous polarization fields across similar layers displaying analogous defect segregation. These results account for the difference in polarity-dependent segregation due to the electric field-driven diffusion of native defects near ZnO interfaces.

Weak temperature and bias dependence of spin accumulation in epitaxial Co70Fe30/MgO tunnel contacts to p-type Ge

Electrical spin accumulation that was robust against changes in temperature and bias voltage was achieved in epitaxial Co70Fe30/MgO tunnel contacts to p-type Ge, with negligible Schottky barrier formation. Hanle and inverted Hanle effects, which are characteristic features of non-equilibrium spin accumulation in the tunnel contacts, were clearly observed up to room temperature for both hole spin injection and extraction. Notably, the obtained spin signal showed weak temperature dependence even at a low bias voltage, and symmetric behavior with respect to bias polarity, which are inconsistent with spin-polarized tunneling via localized states in the contact.

Fabrication and Characterization of Graphene-on-Silicon Schottky Diode for Advanced Power Electronic Design

In this study, graphene-on-silicon process technology was developed to fabricate a power rectifier Schottky diode for efficiency improvement in high operating temperature. Trench-MOS-Barrier-Schottky (TMBS) diode structure was used to enhance the device performance. The main objective of this research was to study the effect of reduced graphene oxide (RGO) deposited on silicon surface for Schottky barrier formation and heat transfer in Schottky junction. The study showed RGO deposited on silicon as a heat spreader could help to reduce the effect of heat generated in the Schottky junction that leads to a leakage current reduction and efficiency improvement in the device. With comparison to the conventional metal silicide (titanium silicide and cobalt silicide), the leakage reduced by two-orders of magnitude when tested under high operating temperature (>100°C). TMBS rectifier diode that uses graphene-based heat spreader could produce highly reliable product able to withstand high temperature operating condition.

Effects of temperature on conduction mechanism, ac electrical and dielectric properties of NdFe0.9Ni0.1O3 by employing impedance spectroscopy

In the present work, the effects of temperature and frequency on the ac electrical and dielectric properties of polycrystalline NdFe0.9Ni0.1O3, prepared by solid-state reaction method, are investigated. From the impedance spectroscopic measurements, three relaxation processes are observed, which are related to grains, grain boundaries and electrode-semiconductor contacts in the measured temperature and frequency range. For NdFe0.9Ni0.1O3 sample, the applicable equivalent circuit model is (R g Q g)(R gb Q gb)(R c Q c) in the measured temperature range. Decrease in resistances and relaxation times of the grains and grain boundaries with temperature confirm the involvement of thermally activated conduction mechanisms. With the increase in temperature, the relaxation frequencies increase for all three processes and the conduction mechanism changes from Mott variable range hole hopping to adiabatic small polaronic hole hopping in this material. The permittivity of grains is from 8 to 10, while the high permittivity observed at higher temperatures is extrinsic (due to Maxwell-Wagner type polarizations), which is primarily due to the formation of different Schottky barriers. The grain boundaries, ceramic surfaces and electrode-semiconductor contacts mainly contribute in the colossal value of permittivity of NdFe0.9Ni0.1O3. The ac conductivity plots show the positive values of the ‘dσ/dT’ which indicate that the charge carriers are localized. The results of conductivity signify that the delocalization of charge carriers augment with increase in the temperature in this system.

Band bending at magnetic Ni/Ge(001) interface investigated by X-ray photoelectron spectroscopy

Abstract We report the molecular beam epitaxy growth of Ni on a clean Ge(001) surface with an intermediate NiGe layer forming at the interface at room temperature. The crystallinity of the substrate is lost after the deposition of more than 2 Ni monolayers. The Schottky barrier formation is investigated by X-ray photoelectron spectroscopy. The method allows us to infer a 0.39–0.45 eV band bending at the interface between the compound and Ge(001). Magneto-optical Kerr effect measurements were conclusive in detecting the ferromagnetic ordering of Ni outermost layers.

Impact of Yb, In, Ag and Au thin film substrates on the crystalline nature, Schottky barrier formation and microwave trapping properties of Bi2O3 films

The effect of the Yb, In, Ag and Au thin film metal substrates on the structural and electrical properties of Bi2O3 thin films are investigated by means of X-ray diffraction, impedance spectroscopy an current-voltage characteristic techniques. The Bi2O3 films are observed to exhibit a crystallization nature depending on the crystal structure of the substrate. Particularly, when the metal substrate is facing centered cubic, the Bi2O3 prefers the γ− phase of body centered cubic crystallization for the (Yb, Ag and Au)/Bi2O3 interfaces. Whereas when a tetragonal substrate (indium) is used, the tetragonal β−Bi2O3 single phase is preferred. All structural parameters presented by the lattice constant, degree of orientation, dislocation density, micro-strain and grain size are observed to strongly depend on the crystal type. In addition, the evaluation of the Schottky barrier formation at the (Yb, In, Ag, Au)/Bi2O3/Au interfaces by the current-voltage characteristics, revealed that the (In, Au)/Bi2O3/Au interface exhibit ohmic nature of contact and the (Yb, Ag)/Bi2O3/Au are of Schottky type, the rectification ratio for the Yb/Bi2O3/Au interface reaches a value of 105 indicating the applicability of these interfaces in CMOS digital logic devices. Moreover, the impedance spectroscopy analysis revealed that the ohmic interfaces exhibit a negative capacitance effect. The In/β−Bi2O3/Au and Yb/γ−Bi2O3/Au interfaces are performing as microwave traps with wave absorption percentage of 62% and 92% at frequencies of 193 and 1200MHz, respectively. The features of the devices are promising as they indicate the applicability as microwave resonator and fast electronic switches.

On the junction physics of Schottky contact of (10, 10) MX2 (MoS2, WS2) nanotube and (10, 10) carbon nanotube (CNT): an atomistic study

Armchair nanotubes of MoS2 and WS2 offer a sizeable band gap, with the advantage of a one dimensional (1D) electronic material, but free from edge roughness and thermodynamic instability of nanoribbons. Use of such semiconducting MX2 (MoS2, WS2) armchair nanotubes (NTs) in conjunction with metallic carbon nanotubes (CNT) could prove useful for nanoelectronics and photonics applications. In this work atomistic simulations of MoS2 NT-CNT and WS2 NT-CNT junctions are carried out to study the physics of such junctions. With density functional theory (DFT) we study the carrier density distribution, effective potential, electron difference density, electron localization function, electrostatic difference potential and projected local density of states of such MX2 NT-CNT 1D junctions. Thereafter the conductance of such a junction under moderate bias is studied with non-equilibrium Greens function (NEGF) method. From the forward bias characteristics simulated from NEGF, we extract diode parameters of the junction. The electrostatic simulations from DFT show the formation of an inhomogeneous Schottky barrier with a tendency towards charge transfer from metal and chalcogen atoms towards the C atoms. For low bias conditions, the ideality factor was calculated to be 1.1322 for MoS2 NT-CNT junction and 1.2526 for the WS2 NT-CNT junction. The Schottky barrier heights displayed significant bias dependent modulation and are calculated to be in the range 0.697 - 0.664eV for MoS2 NT-CNT and 0.669-0.610 eV for the WS2 NT-CNT respectively.

Evidence of Plasmonic Induced Photocatalytic Hydrogen Production on Pd/TiO2 Upon Deposition on Thin Films of Gold

H2-production from renewables using sunlight is probably the holy grail of modern science and technology. Among the many approaches for increasing reaction rates, by increasing light absorption, plasmonic materials are often invoked. Yet, most plasmonic metals on semiconductors are also good for Schottky barrier formation. In this work, we are presenting evidences of de-coupling the plasmonic from Schottky effects on photoreaction. To conduct this we have systematically changed the under-layer gold film thickness and associated particle size. On top of the thin film layer, we have deposited the exact amount of a prototypical Schottky-based photo-catalyst (Pd/TiO2). We found up to 4 times increase in the H2-production rate at a critical Au film thickness (8 nm-thick). Below this thickness, the plasmonic response is not too strong while above it, the PR decays in favor of the Drude absorption mode. The reaction requires the presence of both UV (to excite the semiconductor) and visible light (to excite Au particles) in order to obtain high hydrogen production, 800 µmol/gCatal.min (probably the highest direct hydrogen (not current) production rate reported on a performing catalyst). The enhancement origin is quantitatively traced to its computed electric field strength (EFS). Adding a dielectric (SiO2) in between the Au thin layer and the catalyst exponentially decreased the reaction rate and EFS, with increasing its thickness. This work indicates the possibility of making an active and stable photo-catalyst from fundamental concepts yet further progress on the structural (technological) front is needed to make a practical catalyst.Graphical abstract

Visible and direct sunlight induced H2 production from water by plasmonic Ag-TiO2 nanorods hybrid interface

This report signifies the synthesis of TiO2 nanorods (TNR ~79nm) and nanospheres (TNS ~19nm) and their Ag loaded counterparts AgTNR and AgTNS for the photocatalytic hydrogen production from water under monochromatic visible and direct sunlight. The Ag-TNR nanohybrid junction was sensitized at a matching monochromatic wavelength of 457nm and sunlight to produce ~90 µmol and 105 µmol of gas, respectively, increase in the efficiency is explained due to the surface plasmon (SPR) effect of Ag nanoparticles and is also correlated to fluorescence quenching (due to better charge distribution along larger nano-interface), crystal structure and surface area (146m2g−1) of fabricated AgTNR nanocomposite. The elongated morphology of AgTNR led to the effective distribution of charge along larger interface resulting in the increase of photocurrent density (0.01mA/cm2) which boosts the reaction rate. Plasmonic metal (Ag) activated with matching wavelength to SPR produces an electric field and the TiO2 present in the proximity encounters these effects results in the formation of Schottky barrier, the SPR effect is also more towards Ag-TiO2 interface which results in the ejection of electron towards the conduction band of TNR.This study demonstrated that Ag nanoparticles loaded lengthy TiO2 nanorods (~79nm) exhibited highly improved H2 production (90 μmol) from water relative to TiO2 nanospheres (~19nm) due to the plasmonic effect at 457nm light irradiation that also exhibited better H2 production (105 μmol) rate under direct sun light (8h) exposure.

(Invited) Performance Limit and Potential of Layered MoTe2 Transistors

Atomically thin flaks were obtained to fabricate field-effect transistors by using mechanical exfoliation of 2H-type α-molybdenum ditelluride (MoTe2) bulk crystal grown by chemical vapor transport. Both static and dynamic charge transport of these layered transistors were systematically investigated to explore the underlying mechanism of charge transport. In the quasi-static measurements, carrier ambipolarity was observed and originated from the formation of tunable Schottky barriers at the metal/MoTe2 contacts. In the dynamic measurements, .the 1/f dependence of the noise was observed in the conducting channels in vacuum and followed the carrier number fluctuation model. Moreover, the noise spectrum in ambient conditions changed to a Lorentzian, possibly because a large number of gas molecules absorbed at the chalcogen vacancies, enhancing the trapping and emission of carriers between two discrete energy states. Using such unique layered transistors, we further realized complementary-like inverters, amplifiers and environmental sensors, demonstrating their feasibility for future digital and analog circuit applications.

Interfacial Contact Effects in Top Gated Zinc Oxide Thin Film Transistors Grown by Atomic Layer Deposition

Contact effects at the source/drain (S/D) electrodes in thin film transistors (TFTs) based on zinc oxide (ZnO) utilizing the top gate, bottom contact geometry are investigated using electrical and material studies. Low temperature atomic layer deposition (ALD) is employed to directly grow the ZnO active layer on Au, Ru, and TiW bottom electrodes. TFT performance varies significantly depending on the S/D metallization scheme. Au contacts are seen to uniquely promote the growth of a highly n-doped ZnO channel that degrades the TFT’s output impedance and controllability. On the other hand, TiW contacts suffer from poor carrier injection because of Schottky barrier formation. The best overall performance is demonstrated by Ru/ZnO TFTs based on their excellent switching capabilities alongside a moderately high mobility. From X-ray photoelectron spectroscopy measurements, the superior performance of Ru is the consequence of an oxidation-free interface that inhibits the adsorption of hydroxide surface dopants. Thus, the surface chemistry of the metal contact plays a large role on the ZnO growth and metal/ZnO interface energetics.

Manipulating the structure of polyaniline by exploiting redox chemistry: Novel p-NiO/n-polyaniline/n-Si Schottky diode based chemosensor for the electrochemical detection of hydrazinobenzene

New and effective chemosensor was fabricated using p-nickel oxide (NiO)/n-conducting polyaniline (PANI) based Schottky barrier diode for the detection of hydrazinobenzene chemical. The n-PANI was synthesized through in-situ chemical doping of PANI EB by using calcium hydride as dopant and subjected to elemental analysis, optical, structural and morphological properties. The appearance of a non-linear I–V behavior at the interface of Pt and p-NiO/n-PANI layer confirmed the formation of Schottky junction of the fabricated Pt/p-NiO/n-PANI/n-Si Schottky barrier diode. The electrochemical properties of Pt/p-NiO/n-PANI/n-Si Schottky barrier diode towards the detection of hydrazinobenzene were elucidated by cyclovoltametry (CV) measurements. The sensing results revealed that the Pt/p-NiO/n-PANI/n-Si Schottky barrier diode exhibited a stable, reliable high sensitivity ∼90.5μAmM−1cm−2, good detection limit of ∼5.11μM with correlation coefficient (R) of ∼0.99417 and short response time (10s). Herein, n-type chemical doping of PANI and the formation of Schottky barrier elicited the sensing parameters such as sensitivity, detection limit and correlation coefficient.

Monolayer borophene electrode for effective elimination of both the Schottky barrier and strong electric field effect

The formation of Schottky barriers between 2D semiconductors and traditional metallic electrodes has greatly limited the application of 2D semiconductors in nanoelectronic and optoelectronic devices. In this study, metallic borophene was used as a substitute for the traditional noble metal electrode to contact with the 2D semiconductor. Theoretical calculations demonstrated that no Schottky barrier exists in the borophene/2D semiconductor heterostructure. The contact remains ohmic even with a strong electric field applied. This finding provides a way to construct 2D electronic devices and sensors with greatly enhanced performance.