Schottky Barrier Enhancement Research Articles

Enhanced Schottky barrier engineering in silver-doped TiO2/p-Si heterojunctions: Insights into electrical behavior and charge carrier dynamics

Heterojunctions were fabricated through the deposition of silver-doped Titanium dioxide (Ag–TiO2) onto p-type crystalline silicon, employing the sol-gel technique. Electrical characterization was conducted with varying Ag concentrations. The investigation revealed that the Schottky barriers at each interface (Ag/TiO2 and Si/Ag), along with the built-in potential at the TiO2/p-Si junction, increase proportionally with the Ag concentration. This observed trend was attributed to the reduction in the TiO2 bandgap due to Ag incorporation, resulting in a concurrent shift in both valence and conduction bands. Consequently, there is a growth of the conduction energy discontinuity and a reduction in the valence one, facilitating hole diffusion while impeding electron transfer across the depletion layer. Furthermore, the introduction of Ag leads to a decrease in both electron and hole concentrations. However, Ag incorporation within the TiO2 matrix manifests as nanoparticles and clusters, resulting in a nonhomogeneous distribution of charge carriers across the sample. Impedance analysis indicates an increase in device resistance and a decrease in effective capacitance.

Effects of In2O3 doping on the microstructure and electrical properties of ZnO–V2O5–Nb2O5 varistor ceramics

To understand the effects of In2O3 on the microstructure, grain size dispersion, density and nonlinear electrical characteristics, ZnO–V2O5–Nb2O5 varistor ceramics with 0.02, 0.05 and 0.1 mol.% In2O3 were fabricated via sintering at 950–975 °C for 1 h. The sintered samples were evaluated by x-ray diffraction, scanning electron microscopy, density measurements and electrical measurements through a voltage source meter. In2O3 addition improves relative density to ≥99 % and acts as an efficient grain growth inhibitor, resulting in a narrower grain dispersion and finer ZnO grains due to the formation of In–V–O intergranular phases. The breakdown potential (E1mA) increases sharply to 7.49 ± 0.3 kV/cm (from 1.66 ± 0.1 kV/cm) as a result of grain size reduction to 2.1 ± 0.1 μm (from 3.89 ± 0.2 μm) with In concentration of 0.1 mol.% (from 0.02 mol.%). Doping of In2O3 improves the nonlinear exponent and reduces the leakage current density as a direct consequence of enhanced Schottky barrier height.

Cold-Sintered ZnO Ceramic Composites Co-Doped with Polytetrafluoroethylene and Oxides.

Grain boundaries play a significant role in determining the performance of ceramic-based materials. The modulation of interfacial structures provides a promising approach to improve the physicochemical and electrical properties of ceramic materials. In this work, the grain boundary structures of ZnO-based ceramics were manipulated by incorporating polytetrafluoroethylene (PTFE) and metal oxides through the cold sintering process (CSP). It was found that the grain size of ZnO-based ceramics can be effectively reduced from 525.93 nm to 338.08 nm with an addition of PTFE and metal oxides of CoO and Mn2O3. Microstructural results show that most of the PTFE phase and metal oxides were distributed along the grain boundaries, which may lead to the increased grain boundary resistance from 1.59 × 106 ohm of pure ZnO to 6.21 × 1010 ohm of ZnO-based ceramics doped with PTFE and metal oxides, and enhanced Schottky barrier height from 0.32 eV to 0.59 eV. As a result, the breakdown field and nonlinear coefficient of the ZnO-based ceramics were improved to 3555.56 V/mm and 13.55, respectively. Therefore, this work indicates that CSP presents a feasible approach to design functional ceramic composites through the integration of polymer and metal oxides.

Back-to-back Schottky junction photodetectors based on CVD grown CsPbBr3 microcrystalline striped films

In recent years, a new type of lead halide perovskite has attracted a lot of attention for next-generation photodetectors (PDs) with high responsivity, good detectivity, and fast photoresponse speed. Specifically, cesium based all-organic perovskites exhibit better photostability and therefore have achieved increasing success in PDs recently. For reducing the leak current and increasing the response speed of photoconductive PDs, back-to-back Schottky junction PD is designed and fabricated through a direct growth approach of CsPbBr3 microcrystal (MC) films on indium tin oxide (ITO) electrodes by the chemical vapor deposition (CVD) method. Due to the enhanced Schottky barrier height and threshold voltage between CsPbBr3 and ITO electrodes, the PD exhibits the on/off ratio of up to 104, peak responsivity of 3.9 AW−1, detectivity of 3.8 × 1012, and fast response speed of 0.22 ms (rise time) and 0.45 ms (decay time). In addition, the stability of PD is also enhanced by the high crystal quality of CVD grown CsPbBr3 MCs.

Enhanced performance of graphene/GaAs nanowire photoelectric conversion devices by improving the Schottky barrier height

Graphene/nanowire (NW) Schottky junctions have shown great potential in nanoscale photoelectric conversion devices. However, due to the relatively small difference in work functions, the graphene/NW junctions typically have a low Schottky barrier height, which dramatically limits the performance of devices. Here, the authors demonstrate that the performance of graphene/GaAs nanowire photoelectric conversion devices could be significantly enhanced by improving the Schottky barrier height through chemical doping of graphene. After nitric acid treatment, the Schottky barrier height is increased from 0.29 to 0.35 eV, leading to a much lower dark current, larger detectivity, higher on/off ratio, and higher speed due to the enhanced built-in electric field. The open-circuit voltage of the graphene/GaAs nanowire solar cell is significantly increased after doping due to the enhanced Schottky barrier height, yielding a remarkable conversion efficiency of 15.88%. This work provides an effective way for improving the graphene/nanowire junction properties and enabling high performance photoelectric conversion devices.

Effect of gold and iron nanoparticles on photocatalytic behaviour of titanium dioxide towards 1-butyl-3-methylimidazolium chloride ionic liquid

The high water solubility, chemical stability and low volatility of ionic liquids (ILs) have made them potentially persistent than conventional pollutants and toxic to the aquatic organisms. Therefore, extensive research efforts are being directed with an aim to develop cheap and efficient protocols to reduce the uncontrolled release of ILs in the environment. In the same line of action, titanium dioxide (TiO2) loaded with gold and iron nanoparticles were trialled for the photocatalytic degradation of highly concentrated 1-butyl-3-methylimidazolium chloride [BmimCl] ionic liquid. Furthermore, results pertaining to the degradation of the [BmimCl] using TiO2 loaded with gold nanoparticles (AuNPs) were compared with results obtained by using TiO2 loaded with Fe (NO3)3.9H2O and pristine TiO2 under same set of conditions. It was found that TiO2 decorated AuNPs demonstrated 7 times higher photocatalytic degradation for highly concentrated [BmimCl] in 60 min of reaction time in comparison to the pristine TiO2. Congruently, investigations also revealed that TiO2 loaded AuNPs expressed 3.3 times higher photocatalytic degradation of [BmimCl] in comparison to conventional photocatalyst TiO2@Fe under same reaction conditions. The higher photocatalytic performance associated with TiO2 loaded AuNPs was due to the enhanced Schottky barrier, which could have minimized the photocharge carrier resistance separation and migration. The mechanism for photocatalytic degradation of [BmimCl] using TiO2 loaded AuNPs has been also been described.

Low-Power Graphene/ZnO Schottky UV Photodiodes with Enhanced Lateral Schottky Barrier Homogeneity.

The low-power, high-performance graphene/ZnO Schottky photodiodes were demonstrated through the direct sputter-growth of ZnO onto the thermally-cleaned graphene/SiO2/Si substrate at room temperature. Prior to the growth of ZnO, a thermal treatment of the graphene surface was performed at 280 °C for 10 min in a vacuum to desorb chemical residues that may serve as trap sites at the interface between graphene and ZnO. The device clearly showed a rectifying behavior with the Schottky barrier of ≈0.61 eV and an ideality factor of 1.16. Under UV illumination, the device exhibited the excellent photoresponse characteristics in both forward and reverse bias regions. When illuminating UV light with the optical power density of 0.62 mW/cm2, the device revealed a high on/off current ratio of >103 even at a low bias voltage of 0.1 V. For the transient characteristics upon switching of UV light pulses, the device represented a fast and stable photoresponse (i.e., rise time: 0.16 s, decay time: 0.19 s). From the temperature-dependent current–voltage characteristics, such an outstanding photoresponse characteristic was found to arise from the enhanced Schottky barrier homogeneity via the thermal treatment of the graphene surface. The results suggest that the ZnO/graphene Schottky diode holds promise for the application in high-performance low-power UV photodetectors.

Influence of TCO intermediate thin-layers on the electrical and thermal properties of metal/TCO/p-Si Schottky structure fabricated via RF magnetron sputtering

In this paper, versatile Metal/TCO/p-Si Schottky Barrier Diodes (SBDs) with dissimilar TCO intermediate layers (ZnO and ITO) were fabricated by RF magnetron sputtering technique. An overall electrical performance comparison between the Al/ZnO/p-Si, Au/ITO/p-Si and the conventional Au/p-Si structures is carried out. The measured I-V characteristics indicate that the proposed Al/ZnO/p-Si design exhibits an outstanding capability for achieving a high rectifying ratio of 142 dB. This is mainly due to the enhanced Schottky barrier height (SBH) of 0.75 V and close to unite ideality factor (n = 1.23). Such behavior can be attributed to the enhanced interface quality achieved by introducing TCO inter-layers, which could decrease the Series resistance. A comparative study of the elaborated structures performance is carried out in which new Figures of Merit (FoM) parameters that combine both electrical and thermal stability performances are proposed. The Experimental results show that the proposed designs with ITO and ZnO sub-layers exhibits improved FoM parameters as compared to the conventional Au/p-Si structure. Moreover, this comparative study enables to the designer to acquire a comprehensive review about the Si-based SBDs design tradeoffs. It is demonstrated that the insertion of a TCO inter-layer might be beneficial for avoiding the degradation related-heating effects. Therefore, the proposed designs offer the possibility of bridging the gap between superior electrical performance and high thermal stability, which makes them suitable for developing high-performance Schottky solar cells and sensing applications.

Low-dark-current waveguide InGaAs metal–semiconductor–metal photodetector monolithically integrated with InP grating coupler on III–V CMOS photonics platform

The fabrication of waveguide InGaAs metal–semiconductor–metal (MSM) photodetector (PD) monolithically integrated with an InP grating coupler has been demonstrated using the III–V CMOS photonics platform. The grating coupler shows approximately 28% coupling efficiency, which allows wafer-scale testing with better coupling and alignment tolerance than edge-fire coupling. The InGaAs PD with an InP/InAlAs Schottky barrier enhancement (SBE) layer exhibits a low dark current of 0.75 nA at 1 V bias. When the bias is 4 V, a responsivity of approximately 0.19 A/W with 3 nA dark current is achieved. The fabricated PD on a III–V-on-insulator wafer can be used for the fabrication of low-power receiver chips for optical interconnects.

Surface Leakage Reduction in MSM InGaAs Photodetector on III–V CMOS Photonics Platform

By evaluating the leakage current components of Ni/InGaAs Schottky junctions, we have revealed that the surface leakage current was dominant in the dark current of the waveguide metal–semiconductor–metal (MSM) InGaAs photodetector (PD) fabricated on the III–V CMOS photonics platform. To suppress the surface leakage, we have investigated the impact of the InAlAs Schottky barrier enhancement (SBE) layer on the surface leakage. It is found that the surface leakage can be significantly reduced by the surface passivation effect of the InAlAs SBE layer in addition to the reduction in the junction bulk leakage. We have also found that the surface passivation by an improper oxide such as Al2O3 on the SBE layer increased the dark current probably due to the fixed charges in the oxide layer. By introducing the InP/InAlAs SBE layer without any oxide passivation, we have successfully demonstrated the low-darkcurrent MSM InGaAs PD which was monolithically integrated with an InP photonic-wire waveguide fabricated on a III–V-on-insulator wafer. When a bias voltage of 1 V was applied, the dark current of 7 nA was obtained with 0.15 A/W responsivity for a 1550-nm wavelength.

InGaZnO metal‐base transistor with high current gain

The fabrication of metal-base transistors (MBTs) based on InGaZnO at room temperature is reported for the first time. With a suitable oxygen doping to the sputtering-deposited InGaZnO film and an HfSiO interlayer, improved diode performances with enhanced Schottky barrier heights of 0.70 and 0.66 eV are obtained for the base/collector (Ti/InGaZnO) and base/emitter (Au/HfSiO/InGaZnO) junctions, respectively. InGaZnO MBT using a Ti(10 nm)/Au(10 m)/HfSiO(5 nm) dual metal base shows a high common-emitter current gain ( β ) 840-310 at V CE = 2 V and I B ranging from 1 to 10 nA.

Band structure effect on the electron current oscillation in ultra-scaled GaSb Schottky MOSFET: tight-binding approach

This paper explores band structure effect on the quantum transport of a low-dimensional GaSb Schottky MOSFET (SBFET) for the implementation of III---V transistor with a low series resistance. Precise treatment of the full band structure is employed applying sp 3 d 5 s ∗ tight-binding (TB) formalism. A remarkable distinction between the thickness dependent effective masses extracted from the TB and the bulk values imply that the quantum confinement modifies the device performance. Strong transverse confinement leads to the effective Schottky barrier height increment. Owing to the adequate enhanced Schottky barriers at low drain voltages, a double barrier gate modulated potential well is formed along the channel. The double barrier profile creates a longitudinal quantum confinement and induces drain current oscillation at low temperatures. Significant factors that may affect the current oscillation are thoroughly investigated. Current oscillation is gradually smoothed out as the gate length shrinks down in ultra scaled structure. The results in this paper are paving a way to clarify the feasibility of this device in nanoscale regime.

Tight-binding analysis of current oscillation in nanoscale In0.53Ga0.47As Schottky MOSFET

A comprehensive study of band structure effect on the quantum transport of nanoscale In0.53Ga0.47As Schottky MOSFET for the implementation of III–V MOSFET with low source/drain series resistance is presented. Rigorous treatment of the full band structure in ultra-thin body MOSFET is employed using sp3d5s* tight-binding approach. Strong transverse confinement increases the energy of subbands and, indeed, the effective Schottky barrier height. Due to enhanced Schottky barriers and at low drain voltages, a double barrier gate modulated potential well is created along the channel that results in source-to-drain confinement of states. As tunnelling is the main current component in this device, longitudinal confinement induces drain current oscillation at low temperatures. Important factors that may affect current oscillation are demonstrated. Current oscillation that alters the normal performance of the device is investigated in nanowire Schottky MOSFET, as well. Additional quantum confinement in nanowire Schottky MOSFET provides higher effective Schottky barrier height than the double gate structure. Accordingly, the drain current oscillation is more apparent in nanowire Schottky MOSFET than in the double gate device and is gradually smoothed out as the gate length shrinks down in ultra-scaled structure. Effect of diffusive scattering on the quantum transport of the device is investigated, too. What is prominent in our result is that the drain current oscillations degrade as the channel mobility is decreased. The results in this paper are paving a way to elucidate the feasibility of this device in the nanoscale regime.

Tight-binding study of quantum transport in nanoscale GaAs Schottky MOSFET

This paper explores the band structure effect to elucidate the feasibility of an ultra-scaled GaAs Schottky MOSFET (SBFET) in a nanoscale regime. We have employed a 20-band sp3d5 s* tight-binding (TB) approach to compute E — K dispersion. The considerable difference between the extracted effective masses from the TB approach and bulk values implies that quantum confinement affects the device performance. Beside high injection velocity, the ultra-scaled GaAs SBFET suffers from a low conduction band DOS in the Γ valley that results in serious degradation of the gate capacitance. Quantum confinement also results in an increment of the effective Schottky barrier height (SBH). Enhanced Schottky barriers form a double barrier potential well along the channel that leads to resonant tunneling and alters the normal operation of the SBFET. Major factors that may lead to resonant tunneling are investigated. Resonant tunneling occurs at low temperatures and low drain voltages, and gradually diminishes as the channel thickness and the gate length scale down. Accordingly, the GaAs (100) SBFET has poor ballistic performance in nanoscale regime.

A model bismuth oxide intergranular thin film in a ZnO twist grain boundary

The electronic properties of a model bismuth oxide intergranular film in ZnO wereinvestigated using density functional plane wave calculations. It was found that oxygenexcess plays a fundamental role in the appearance of electrical activity. The introduction byoxygen interstitials or zinc vacancies results in depletion of the charge in deep gap statesintroduced by the bismuth impurities. This makes the boundary less metallic and promotesthe formation of acceptor states localized to the boundary core, resulting in Schottkybarrier enhancement. The results indicate that the origin of electrical activity in thinintergranular bismuth oxide films is probably not distinct from that in decorated ZnOboundaries.

Novel Silicon-Carbon (Si:C) Schottky Barrier Enhancement Layer for Dark-Current Suppression in Ge-on-SOI MSM Photodetectors

This letter reports the first demonstration of an evanescent coupled germanium-on-silicon-on-insulator (Ge-on-SOI) metal-semiconductor-metal (MSM) photodetector with a novel silicon-carbon (Si:C) Schottky barrier enhancement layer. Through the insertion of a Si:C barrier layer between the metal/Ge interface, the hole Schottky barrier height phibh can effectively be enhanced to ~0.52 eV above the valence band edge. As a result, significant dark-current IDark suppression by more than four orders of magnitude was demonstrated, leading to an impressive IDark of ~11.5 nA for an applied bias VA of 1.0 V. Optical measurements performed at a photon wavelength of 1550 nm revealed the achievement of good internal responsivity and quantum efficiency of ~530 mA/W and 42.4%, respectively, making such a high-performance Ge-on-SOI MSM photodetector a promising option for optical communication applications.

High-Performance Waveguided Ge-on-SOI Metal–Semiconductor–Metal Photodetectors With Novel Silicon–Carbon (Si : C) Schottky Barrier Enhancement Layer

We report the demonstration of waveguided germanium-on-silicon-on-insulator metal-semiconductor-metal (MSM) photodetectors with novel silicon-carbon (Si:C) Schottky barrier enhancement layer. Significant suppression of dark current (/dark) by ~4 orders of magnitude was achieved over a conventional MSM photodetector due to an enhanced hole Schottky barrier height of 0.52 eV. At an applied bias V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> of 1.0 V a -3-dB bandwidth of ~12 GHz at an incident wavelength of 1550 nm was demonstrated. Optical measurements performed at photon wavelengths lambda of 1520-1570 nm reveal a uniform spectral response and quantum efficiency of ~760 mA/W and ~60%, respectively, demonstrating an effective photodetection for the entire C-band spectrum range.

Demonstration of AlGaN/GaN High Electron Mobility Transistors on a-Plane (1120) Sapphire

The AlGaN/GaN heterostructures (HSs) with reduced dislocation density were grown on 4-in. a-plane sapphire substrate. The two-dimensional electron gas (2DEG) was observed for AlGaN/GaN HSs on a-plane sapphire. A complete pinch off AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated with a maximum drain current density (IDSmax) of 551 mA/mm and transconductance maximum (gmmax) of 134 mS/mm. Compared to c-plane grown HEMTs, two orders of magnitude low gate leakage current was observed on a-plane grown HEMTs with enhanced barrier height. The low gate leakage is due to enhanced Schottky barrier height and reduced dislocation density of GaN grown on a-plane sapphire.

Interfacial differences in enhanced schottky barrier height Au/n-GaAs diodes deposited at 77 K

The use of cryogenic temperatures (∼77 K) during Au Schottky contact deposition onto n-GaAs produces an increase in barrier height from 0.73 eV for room temperature diodes to 0.82 eV. Not all Schottky metals show this enhancement—for example Pt and Ti do not show any significant change in barrier height whereas Au, Pd and Ni show increases between 7 and 18%. We used X-ray reflectivity to show that the main difference between Au deposited at 77 K and room temperature is a decreased metal roughness while the interfacial roughness between the Au and GaAs is basically the same. As the diodes are annealed to 300 °C both the difference in barrier height and interfacial roughness is lost. This is a simple method with potential for improving the performance of GaAs metal-semiconductor-field-effect-transistors (MESFETs).

Improvement of Mesa-Sidewall Leakage Current Using Benzocyclobuten Sidewall Process in InGaAs/InP MSM Photodetector

In recent decades, metal-semiconductor-metal (MSM) photodetector for optical fiber communication applications have been studied extensively. The dark current in MSM PD is an important parameter that can be reduced by schottky barrier enhancement and fabrication process. By employing a benzocyclobuten (BCB) sidewall passivation process, the leakage issue between Schottky metal fingers and mesa sidewalls can be avoided. Moreover, the parasitic capacitance can also be decreased due to the low dielectric constant of BCB. The BCB passivation process decreases the dark current density from 11 nA/µm2 to 5.7 pA/µm2.