Schottky Barrier Height Variation Research Articles

Asymmetric Schottky contacts induced via localized ultrafast laser irradiation for ultrasensitive, self-powered, 2D photodetectors

Self-powered photodetectors hold great promise for addressing power-related challenges in the “Internet of Things (IoT)” era. However, the self-powered performances of a metal-semiconductor-metal (MSM) structure photodetector are inherently limited due to the presence of the symmetric Schottky contacts, leading to canceling photocurrents in opposite directions, while constructing an asymmetric MSM structure demands complicated design or sustained external fields. Herein, we propose a novel contact engineering strategy based on localized femtosecond (fs) laser irradiation, achieving an asymmetric band structure in an MSM-structure photodetector with pristine symmetric Schottky contacts. As a result, a MoS2 photodetector that exhibits exceptional photoresponse and self-powered performances is successfully fabricated. The device type transitions from a photoconductor to a photodiode, exhibiting a significant improvement in the rectification ratio from 1 to > 104. A comprehensive study on fs laser-based contact engineering is conducted by investigating atom diffusion, element variation, and Schottky barrier height variation. Notably, the photodetector demonstrates an exceptional zero-bias responsivity of 1.72 A/W, with a short circuit current of 37.2 nA and maximum output electric power of 1.67 nW. Our work provides a new strategy for modifying the energy band structure and facilitates the fabrication of high-performance self-powered photodetectors.

A high-performance quasi-vertical MoSe2 photodiode with ultra-low dark current

Van der Waals heterostructure based on 2D materials is a promising technology for high-performance optoelectronic devices because of its tunable bandgaps and optical properties. However, photodetectors with a low dark current and a fast response speed commonly lose their photoresponsivity. The recovery current induced by the Schottky barrier height variation cancels out the device's reverse bias current in this paper, resulting in a quasi-vertical MoSe2 photodiode with ultralow dark current (<1 pA). Simultaneously, rapid electron–hole pair separation occurs at the interface due to the large heterojunction area and the strong interlayer coupling of MoSe2/graphene heterojunction, resulting in a fast response time of 1.5 ms and a high photoresponsivity of 19.72 A/W. Furthermore, the Au/MoSe2 forms a Schottky contact, which is asymmetrical to the Ohmic contact formed by the MoSe2/graphene, enabling the proposed device to achieve high-performance self-powered photodetection. Our work shows an alternative approach to improve the performance of future electronic and optoelectronic applications.

The Variation of Schottky Barrier Height Induced by the Phase Separation of InAlAs Layers on InP HEMT Devices

We investigated the effect of phase separation on the Schottky barrier height (SBH) of InAlAs layers grown by metal–organic chemical vapor deposition. The phase separation into the In-rich InAlAs column and Al-rich InAlAs column of In0.52Al0.48As layers was observed when we grew them at a relatively low temperature of below 600 °C. From the photoluminescence spectrum investigation, we found that the band-gap energy decreased from 1.48 eV for a homogeneous In0.52Al0.48As sample to 1.19 eV for a phase-separated InxAl1−xAs sample due to the band-gap lowering effect by In-rich InxAl1−xAs (x > 0.7) region. From the current density–voltage analysis of the InAlAs Schottky diode, it was confirmed that the phase-separated InAlAs layers showed a lower SBH value of about 240 meV than for the normal InAlAs layers. The reduction in SBH arising from the phase separation of InAlAs layers resulted in the larger leakage current in InAlAs Schottky diodes.

Room Temperature Hydrogen Sensor Using Schottky Contacted Zinc Oxide Thin-Film Transistor: A Comprehensive Investigation

A ZnO-based Schottky thin-film transistor (TFT) utilizing palladium-titanium (Pd-Ti) source/drain electrodes as a sensing medium is used to fabricate a room temperature (RT) hydrogen sensor. In the absence of any heating element, the fabricated sensor is capable of reducing the design complications and power consumption considerably. The RT sensor response was realized with respect to drain current rise owing to the Schottky barrier height reduction depending on the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration (500-4500 ppm). For 500-ppm (minimum detection level) and 4500-ppm (maximum detection level) H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas concentrations, sensor responses of 18% and 78.2% with 65 s/35 s and 10.2 s/85 s response/recovery times are acquired, respectively. The Pd-Ti/ZnO Schottky barrier height variation is attempted to explain the incorporating energy band diagrams of the ZnO channel between source/drain electrodes at different gate and drain bias conditions. Performance analysis of the sensor in terms of repeatability, selectivity toward H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> over methane and acetone, hysteresis, reliability, and humidity exposure has also been examined.

Effects of electric field and strain on the Schottky barrier of the bilayer van der Waals heterostructures of graphene and pure/hydrogenated PC3 monolayer

The carbon-based van der Waals (vdW) heterostructures with metal-semiconductor (M-S) junction have shown great potential for nanodevices and optoelectronic applications; however, the Schottky barrier at interface restricts the injection efficiency of charges. Here, we systematically investigate the effect of the electronic field and biaxial strain on the electronic properties and the Schottky barrier height (SBH) of the PC 3 /graphene(G) and PC 3 H/G vdW heterostructures through first-principles calculations. The results show that the charge redistribution at interface leads to a shift of the Fermi level, which determines the contact type and height of the Schottky barrier. Moreover, the contact type could be tuned from p-type Schottky contact to Ohmic contact by electronic field or in-plane biaxial strain, thus obtaining highly efficient charge transfer. Most importantly, we demonstrate that hydrogenation of PC 3 is an effective strategy to partly screen the external electronic field, whereas more sensitive to strain for inducing the contact type transform and SBH variation of the PC 3 H/G heterostructure . This work provides a promising to design novel carbon-based nonmetal vdW heterostructures and explore their potential applications in electronic and optoelectronic devices . • The hydrogenation of PC 3 is first proposed to be an effective strategy to effectively screen the external electronic field. • The contact type and SBH of PC 3 H/G are more sensitive to external electronic field and biaxial strain than PC 3 /G. • The redistribution of interfacial charge and the shift of Fermi level determine the transition of Schottky barrier. • The PC 3 /G and PC 3 H/G heterostructures have potential applications in nano-electronic and optoelectronic devices.

Interfacial resistive switching of Ruddlesden–Popper phase strontium titanate thin film by charge-modulated Schottky barrier

Ruddlesden–Popper (RP) phase Sr2TiO4 thin film is deposited successfully on FTO/glass substrate by spin coating. X-ray diffraction (XRD) pattern shows high-intensity (00 l) (l = 2, 4, and 6) peaks. The device shows bipolar resistive switching (RS) effect. Analysis on current–voltage (I-V) characteristic shows that conduction mechanism is dominated by Schottky emission in both low resistive state (LRS) and high resistive state (HRS). A variation (~0.12 eV) in Schottky barrier height (SBH) is observed between HRS and LRS. Thus, RS at electrode-Sr2TiO4 interface is the main mechanism. In general, variation of SBH is induced by accumulation of interfacial charges. Polarization-voltage (P-V) measurement shows hysteresis loop, which indicates the accumulation of interfacial charges. Formation and migration of charged oxygen vacancies and ions is proposed to be a possible mechanism of interfacial charges accumulation. This study paves the avenue for exploring RS application based on RP phase Sr2TiO4 perovskite oxide.

Investigation of Parameters for Schottky Barrier (SB) Height for Schottky Barrier Based Carbon Nanotube Field Effect Transistor Device

The design and development of Schottky Barrier Carbon Nanotube Field Effect Transistor (SB CNTFET) is still in the primitive research phase for its utilization in digital design. There is an immediate requirement for the analysis of parametric relations with structural factors to benefit the researchers working in this field. This work helps in the improvement of SB based CNTFET devices to be used in the development of various circuit applications. In this work, investigation of Schottky Barrier height on the performance of SB CNTFET for various geometrical and physical design parameters at the device level has been reported. The analysis of various device parameters of carbon nanotube, i. e., chirality, diameter, band gap, oxide thickness and dielectric constant has been carried out viz. subthreshold conduction, and ION/IOFF ratio. The paper also reports the effect of high dielectric constant material in SB CNTFET with oxide thickness along with Schottky Barrier Height Variation. The performance of SB CNTFET with variation in Schottky Barrier height and temperature variation is also reported. The results obtained indicate that performance of SB based CNTFET can be modified by the proper choice of chirality, dielectrics, oxide thickness and operating temperature. The SB parameter can be optimized by proper choice of metal contact in case of CNTFET.

Physical, photochemical, and extended piezoelectric studies of orthorhombic ZnSnN2 nanocolumn arrays

This study reports the piezo-related properties of ZnSnN2 (ZTN) fabricated through natural Sn3N4 and Zn thickness gradients deposited oppositely on a fluorine-doped tin oxide substrate to form Zn–Sn3N4 composition spreads to enhance the relative variation of the cation ratios and to promote the formation of orthorhombic ZTN. No moving shutter was incorporated into combinatorial magnetron sputtering to minimize fabrication complexity. The Sn3N4-rich deposition (Location 1) of the Zn–Sn3N4 composition spread exhibited Sn3N4 and the single crystallinity of orthorhombic (Pna21) ZTN nanocolumn arrays, which grew along the [0 0 1] direction, confirmed by locked-coupled X-ray diffraction and transmission electron microscopy. The constituent element diffusion and variation of the atomic binding state of constituent elements along the substrate normal were tracked by depth profiling using secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. The band gap of ZTN (approximately 2.0 eV) was estimated from a UV–vis spectrum. The piezotronic and piezophototronic effects of ZTN were determined through a facile current–voltage measurement, which were explained by the Schottky barrier height variations. Piezophotocatalysis exhibited the highest rate constant (k, approximately 9 × 10−3/min) of the measurements, which was attributed to the reduced recombination of the photogenerated e−–h+ pairs because of the piezopotential distribution. Additionally, O2− radicals were predominately indicated in the degradation process.

Piezotronic and Piezophototronic Properties of Orthorhombic ZnSnN2 Fabricated Using Zn–Sn3N4 Composition Spreads through Combinatorial Reactive Sputtering

This paper presents a combinatorial methodology for fabricating orthorhombic ZnSnN2 (ZTN) by using Zn–Sn3N4 composition spreads. This study is the first to verify the substantial piezotronic and piezophototronic features of ZTN on the basis of asymmetric current–voltage (I–V) characteristics. Regarding the piezophototronic effect, at a −5 V bias, the current density was enhanced up to 2.5 times when the applied pressure increased from 0.625 to 2.5 GPa. Schottky barrier height variations at S1 and S2 were calculated under a pressure of 2.5 GPa and were observed to have increased and decreased by approximately 1.0 and 22 mV, respectively. The results clarified the I–V behavior and also supported the proposed energy-band structure evolution of piezotronic and piezophototronic ZTN. In addition, ZTN formation was verified through X-ray photoelectron spectroscopy and X-ray diffraction. A deconvolution algorithm was employed to validate the ratio of orthorhombic ZTN (Pna21) (approximately 30%). In addition, UV–v...

An Investigation on Electrical and Hydrogen Sensing Characteristics of RF Sputtered ZnO Thin-Film With Palladium Schottky Contacts

Fabrication and characterizations of a hydrogen sensor with palladium Schottky contacts, grown on radio frequency sputtered zinc oxide thin film is reported. Temperature dependence performance analysis of the proposed sensor was carried out at different hydrogen concentrations (50–1000 ppm) and temperatures (25°C–200°C) using current–voltage ( $I$ – $V$ ) measurements. Lateral shifts have been observed in the Schottky diode $I$ – $V$ characteristic when the device was exposed to hydrogen, and this could be attributed to the reduction of Schottky barrier height (SBH). The optimum performance of the sensor was obtained at 150 °C with maximum SBH variation of 144 meV at 1000 ppm hydrogen. Transient sensor performance at optimum temperature has also been analyzed and sensitivities ranging from 224% to 1125% with a minimum response time of 55 s and a recovery time of 26 s have been obtained. The response of sensor toward methane and nitrogen dioxide is also discussed. The basic $I$ – $V$ and capacitance–voltage characteristics of Pd/ZnO thin film are also reported, which confirmed its excellent rectifying properties. The basic microstructure studies of ZnO thin film were also investigated using X-ray diffraction, scanning electron microscope, atomic force microscopy, energy dispersive X-ray spectroscopy, and photoluminescence measurements. The proposed sensor has proven to be economical, due to its high sensitivity and easy to fabricate structure with a limited number of processing steps.

Piezopotential‐Induced Schottky Behavior of Zn1−xSnO3 Nanowire Arrays and Piezophotocatalytic Applications

This article presents the piezotronic‐ and piezophototronic effect‐enhanced photocatalysis (piezophotocatalysis) of Zn1−xSnO3 (ZTO) nanowires fabricated through a two‐step hydrothermal reaction. The highlights of this research include (1) tailoring hydrothermal synthesis parameters to obtain well‐aligned LN‐type single‐crystalline ZTO nanowire arrays; (2) exploring the piezopotential‐driven piezotronic and piezophototronic effects of ZTO nanowires; (3) identifying Schottky barrier height variations; and (4) exploiting synergistic piezophotocatalysis for decomposing methylene blue (MB). Transmission electron microscopy, electron probe energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy analyses reveal highly crystalline Zn‐deficient ZTO nanowires. The band gap is estimated to be approximately 3.8 eV. The ZTO nanowires exhibit piezopotential‐modulated piezotronic and piezophototronic effects. The corresponding Schottky barrier height variation is calculated using thermionic emission‐diffusion theory. The calculated photodegradation rate constant k of the sample, under pressure from ultrasonic vibration and a piece of glass, is approximately 1.5 × 10−2 min−1, approximately four times higher than that of ZTO nanowires in the absence of stress. The observed synergistic piezophotocatalysis is attributed to (1) band bending of ZTO nanowires; (2) application of alternating ultrasonic vibration; (3) MB mass transfer enhancement; and (4) abundant active reaction sites generated from ZTO nanowire surface sweeping.

On the mechanism of ultrasonic loading effect in silicon-based Schottky diodes

The influence of ultrasonic loading on current–voltage characteristics of Mo/n–n+–Si structures has been investigated. The research of Schottky barrier height variation has been carried out for various ultrasonic waves frequency (4.1, 8.4, and 27.8MHz), intensity (up to 0.8W/cm2) and loading temperature (160–330K). The obtained results have been analyzed on account of the dislocation nature of the interface patches and model of ultrasound absorption by dislocation kinks. The values of the kink diffusion activation energy Wk=(90±10)meV and the frequency parameter fk=(3±2)·109Hz have been determined.

Analytical modeling of Schottky tunneling source impact ionization MOSFET with reduced breakdown voltage

In this paper, we have investigated a novel Schottky tunneling source impact ionization MOSFET (STS-IMOS) to lower the breakdown voltage of conventional impact ionization MOS (IMOS) and developed an analytical model for the same. In STS-IMOS there is an accumulative effect of both impact ionization and source induced barrier tunneling. The silicide source offers very low parasitic resistance, the outcome of which is an increment in voltage drop across the intrinsic region for the same applied bias. This reduces operating voltage and hence, it exhibits a significant reduction in both breakdown and threshold voltage. STS-IMOS shows high immunity against hot electron damage. As a result of this the device reliability increases magnificently. The analytical model for impact ionization current (Iii) is developed based on the integration of ionization integral (M). Similarly, to get Schottky tunneling current (ITun) expression, Wentzel–Kramers–Brillouin (WKB) approximation is employed. Analytical models for threshold voltage and subthreshold slope is optimized against Schottky barrier height (ϕB) variation. The expression for the drain current is computed as a function of gate-to-drain bias via integral expression. It is validated by comparing it with the technology computer-aided design (TCAD) simulation results as well. In essence, this analytical framework provides the physical background for better understanding of STS-IMOS and its performance estimation.

Interdiffusion and Charge Transport Across Surface-Modified Current Collectors in Planar SOFCs

Current collectors are a key component of planar SOFCs, separating air and fuel supplied onto the electrodes and connecting the cells in series. One of main challenges in the SOFC technology developments is to suppress degradation processes, often associated with the interconnect materials, and to provide low contact resistivity in oxidizing atmospheres. The present work is focused on the studies of near-surface interdiffusion phenomena in Crofer 22 APU ferritic steel interconnects with Ni-based protective layers. Particular emphasis was centered on the area-specific resistance (ASR) between the current collectors and La0.8Sr0.2MnO3 (LSM) cathodes, which exhibits time dependencies governed by the protective interlayer composition and interface microstructure alterations. The ASR changes, tested during over 30,000 hours at atmospheric oxygen pressure, can be described in terms of a model assuming that the current across the interconnector | LSM interface is essentially controlled by electron transfer via the interfacial Schottky barrier. The experimental observations validate this approach, explaining the junction resistivity and Schottky barrier height variations as a result of metal interdiffusion between the current collector and Ni-based protective coating.

Enhancement of hydrogen sensing performance of a GaN-based Schottky diode with a hydrogen peroxide surface treatment

In this work, enhanced hydrogen sensing characteristics of a GaN-based Schottky diode-type sensor with a GaOx layer are studied and demonstrated. A thin GaOx layer inserted in Pd/GaN interface is oxidized by the immersion in an H2O2 solution at room temperature. Experimentally, a significantly high hydrogen sensing response of 1.8×105 and a large Schottky barrier height variation ratio of 33.1% are found upon exposure to a 1% H2/air gas at 300K. In addition, a very low detection limit of 0.1ppm H2/air at 300K is obtained. These improved properties could be attributed to the effective dissociation of hydrogen molecules and rougher Pd surface caused by the presence of the GaOx layer. The response (recovery) time constant of 13.3 (23.6)s is obtained upon exposure to a 1% H2/air gas at 300K. The related hydrogen adsorption analysis of the proposed device is also studied and demonstrated.

Modeling of hysteretic Schottky diode-like conduction in Pt/BiFeO3/SrRuO3 switches

The hysteresis current-voltage (I-V) loops in Pt/BiFeO3/SrRuO3 structures are simulated using a Schottky diode-like conduction model with sigmoidally varying parameters, including series resistance correction and barrier lowering. The evolution of the system is represented by a vector in a 3D parameter space describing a closed trajectory with stationary states. It is shown that the hysteretic behavior is not only the result of a Schottky barrier height (SBH) variation arising from the BiFeO3 polarization reversal but also a consequence of the potential drop distribution across the device. The SBH modulation is found to be remarkably lower (&amp;lt;0.07 eV) than previously reported (&amp;gt;0.5 eV). It is also shown that the p-type semiconducting nature of BiFeO3 can explain the large ideality factors (&amp;gt;6) required to simulate the I-V curves as well as the highly asymmetric set and reset voltages (4.7 V and −1.9 V) exhibited by our devices.

Nb2O5 Schottky based ethanol vapour sensors: Effect of metallic catalysts

The aim of this paper is to compare the performances of the highly porous Nb2O5 Schottky based sensors formed using different catalytic metals for ethanol vapour sensing. The fabricated sensors consist of a fairly ordered nano-vein like porous Nb2O5 prepared via an elevated temperature anodization method. Subsequently, Pt, Pd and Au were sputtered as both Schottky contacts and catalysts for the comparative studies. These metals are chosen as they have large work functions in comparison to the electron affinity of the anodized Nb2O5. It is demonstrated that the device based on Pd/Nb2O5 Schottky contact has the highest sensitivity amongst the developed sensors. The sensing behaviors were studied in terms of the Schottky barrier height variations and properties of the metal catalysts.

Schottky barrier height systematics studied by partisan interlayer

The ability of the “partisan interlayer” technique in adjusting the Schottky barrier height (SBH), through the insertion of an atomic interlayer preferentially bonded to the semiconductor side of a metal–semiconductor interface, was systematically studied in the present work, focusing on the systematic trends, e.g., the variation of electron affinity shift with the species of adsorbate atoms, the variation of SBH on a specific adsorbate-terminated semiconductor (ATS) surface with metal work function, and the variation of SBH on different ATS surfaces with respect to a specific choice of metal, etc. A general conclusion is drawn, emphasizing the validity and the overall effectiveness of the “partisan interlayer” technique.

Variation of Schottky barrier height induced by dopant segregation monitored by contact resistivity measurements

Change of contact resistivity (ρc) is monitored for evaluation of Schottky barrier height (SBH) variation induced by dopant segregation (DS). This method is particularly advantageous for metal–semiconductor contacts of small SBH, as it neither requires low-temperature measurement needed in current–voltage characterization of Schottky diodes nor is affected by reverse leakage current often troubling capacitance–voltage characterization. With PtSi contact to both n- and p-type diffusion regions, and the use of opposite or alike dopants implant into pre-formed PtSi films followed by drive-in anneal at different temperatures to induce DS at PtSi/Si interface, the formation of interfacial dipole is confirmed as the responsible cause for modification of effective SBHs thus the increase or decrease of ρc. A tentative explanation for the change of contact resistivity based on interfacial dipole theory is provided in this work. Influences and interplay of interfacial dipole and space charge on effective SBH are also discussed.

Tunable Schottky barrier height and surface potential by using hydrogen ions

In this research work, hydrogen ion can be used for Schottky barrier height and surface potential tuning with specific power. The current output of Ohmic and Schottky contacted device would be enhanced from 8.25 μA to 171 μA and 2.84 pA to 1.3 μA (hydrogen plasma power was increased from 0 to 60 W), respectively. With adequate hydrogen plasma power, the transport mechanism (variation of Schottky barrier height and surface potential) can be studied in vacuum and atmosphere environment. In this work, we not only improve the current output but also provide the transport mechanism in vacuum and atmosphere environment. The enhancement and intension of ZnO nanowires device can be achieved by using hydrogen plasma treatment for extensive application.