Schottky Barrier Characteristics Research Articles

Bi–Er–O pre-synthesized phase (Bi1-xErx)2O3 doped ZnO varistors with high nonlinear coefficient and low leakage current

The content of free oxygen Oad at the ZnO grain boundaries has an important impact on the double Schottky barrier and electrical properties of ZnO varistors. In this work, Bi–Er–O pre-synthesized (BE) phase (Bi1-xErx)2O3 (0.25 < x < 0.455) with high conductivity of Oad was prepared using Bi2O3 and Er2O3 as raw materials, and the effects of the BE phase doping on the phase, grain boundary properties, and electrical properties of ZnO–Bi2O3–Sb2O3–Co2O3–MnO2–Cr2O3–SiO2 varistors were studied. XRD analysis shows that the lattice constant of the BE phase (Bi1-xErx)2O3 is between (Bi0.75Er0.25)2O3 and BiErO3. With increasing doping content of the BE phase from 0 to 0.75 wt%, part of Er3+ still exists in the form of the BE phase (Bi1-xErx)2O3 at the ZnO grain boundaries, and its content increases with increasing doping content of the BE phase. The conductivity of Oad in (Bi1-xErx)2O3 is much higher than that in Bi2O3, resulting in the generation of a large number of negative O′ and O″ at the ZnO grain boundaries, and decreasing concentration of the intrinsic point defect zinc interstice Zni. So the donor concentration Nd decreases, the height of the grain boundary barrier increases, the depletion layer widens, and the electrical properties are improved. By analyzing the low-temperature permittivity spectra, it was calculated that with increasing doping content of the BE phase from 0 to 0.75 wt%, the concentration of oxygen vacancy VO• decreases inappreciably, but the concentration of zinc interstice Zni•• decreases by about 23%. When the doping amount of the BE phase is 0.75 wt%, the nonlinear coefficient α of the obtained ZnO varistors is 73.9 ± 0.6, and the leakage current density JL is only 0.3 ± 0.1 μA/cm2. This study provides an important reference for improving the electrical properties of ZnO varistors by manipulating the Bi-rich phase structure to improve the double Schottky barrier characteristics.

Non-contact approach to extract Schottky barrier characteristics for gas sensitive nanostructured interfaces

Formation of high precision nanorod based surface morphologies can be engineered with nanotechnology to mimic the function of sensory hairs. Gas sensitive I-V characteristics unique to these surfaces require initialisation under voltage bias and temperature elevation to exploit their band structures and therefore achieve optimal gas response. Prior to detection, devising effective approaches to optimise nanorod based sensors can provide access and efficient control to downsize and significantly miniaturise current gas sensors. In this work, we devised a novel non-contact analysis approach via ultraviolet photoelectron spectroscopy (UPS) to extract specific band structure parameters specifically to locate particular bias for optimal sensor initialisation. The results from five cases all indicate how fabricated nanostructured Schottky barrier heights can be evaluated from UPS data and how their I-V data are correlated and also validate our band structure postulations. The obtained Schottky barrier height values from simulated band structures provided an optimal biasing condition of 0.8 V for Au-ZnO nanorod hydrogen gas sensory operation at 150 °C, demonstrating experimental validity with gas-electrical measurements. Further, the gas response data show exponential dependence with gas concentration which is highly relevant for programmable trigger response controlled sensing function based applications.

Probing Nanoscale Schottky Barrier Characteristics at WSe2/Graphene Heterostructures via Electrostatic Doping (Adv. Electron. Mater. 9/2022)

Nanoscale Schottky Barrier Characteristics The local Schottky–Mott characteristics determine the quality of electronic interfaces in metal–semiconductor van der Waals heterostructures. In the article number 2200196, Sebastian Wood and co-workers demonstrate how advanced scanning probe microscopy can probe the interface characteristics of monolayer tungsten diselenide on graphene transistors, distinguishing contributions from interface dipoles and graphene work function, and providing evidence for unpinned Fermi levels through electrostatic doping.

Transient characteristics of β-Ga2O3 nanomembrane Schottky barrier diodes on various substrates

In this paper, transient delayed rise and fall times for beta gallium oxide (β-Ga2O3) nanomembrane (NM) Schottky barrier diodes (SBDs) formed on four different substrates (diamond, Si, sapphire, and polyimide) were measured using a sub-micron second resolution time-resolved electrical measurement system under different temperature conditions. The devices exhibited noticeably less-delayed turn on/turn off transient time when β-Ga2O3 NM SBDs were built on a high thermal conductive (high-k) substrate. Furthermore, a relationship between the β-Ga2O3 NM thicknesses under different temperature conditions and their transient characteristics were systematically investigated and verified it using a multiphysics simulator. Overall, our results revealed the impact of various substrates with different thermal properties and different β-Ga2O3 NM thicknesses on the performance of β-Ga2O3 NM-based devices. Thus, the high-k substrate integration strategy will help design future β-Ga2O3-based devices by maximizing heat dissipation from the β-Ga2O3 layer.

Probing Nanoscale Schottky Barrier Characteristics at WSe2/Graphene Heterostructures via Electrostatic Doping

AbstractThe adoption of 2D transition metal dichalcogenide (TMD) based optoelectronic devices is limited by Fermi level pinning effects and consequent large contact resistances upon contacting TMDs with bulk metal electrodes. A potential solution for near‐ideal Schottky–Mott behavior and concomitant Schottky barrier height control is proposed by contacting TMDs and (semi‐)metals in van der Waals heterostructures. However, measurement approaches to directly assess interface parameters relevant to the Schottky–Mott rule on a local scale are still lacking. In the present work, a heterostructure of monolayer tungsten diselenide (WSe2) with monolayer graphene (1LG) and bilayer graphene (2LG) is investigated on a bottom‐gate substrate. Kelvin probe force microscopy and tip‐enhanced photoluminescence measurements at different electrostatic doping induced Fermi levels in graphene enable decoupling and quantification of contributions from the interface dipole and electrode work function. These are used to locally probe Schottky barrier characteristics with below 32 nm lateral resolution, demonstrating that the WSe2/1LG junction operates at the Schottky–Mott limit (S ≈ 1). At the WSe2/2LG junction, a reduction of the interface dipole is directly related to changes in excitonic emission properties. These are attributed to charge transfer modulation across the interface, critical for obtaining high‐performance transfer characteristics in transistors and related devices.

Analysis of Schottky barrier heights and reduced Fermi-level pinning in monolayer CVD-grown MoS2 field-effect-transistors

Chemical vapor deposition (CVD)-grown monolayer (ML) molybdenum disulfide (MoS2) is a promising material for next-generation integrated electronic systems due to its capability of high-throughput synthesis and compatibility with wafer-scale fabrication. Several studies have described the importance of Schottky barriers in analyzing the transport properties and electrical characteristics of MoS2 field-effect-transistors (FETs) with metal contacts. However, the analysis is typically limited to single devices constructed from exfoliated flakes and should be verified for large-area fabrication methods. In this paper, CVD-grown ML MoS2 was utilized to fabricate large-area (1 cm × 1 cm) FET arrays. Two different types of metal contacts (i.e. Cr/Au and Ti/Au) were used to analyze the temperature-dependent electrical characteristics of ML MoS2 FETs and their corresponding Schottky barrier characteristics. Statistical analysis provides new insight about the properties of metal contacts on CVD-grown MoS2 compared to exfoliated samples. Reduced Schottky barrier heights (SBH) are obtained compared to exfoliated flakes, attributed to a defect-induced enhancement in metallization of CVD-grown samples. Moreover, the dependence of SBH on metal work function indicates a reduction in Fermi level pinning compared to exfoliated flakes, moving towards the Schottky–Mott limit. Optical characterization reveals higher defect concentrations in CVD-grown samples supporting a defect-induced metallization enhancement effect consistent with the electrical SBH experiments.

Yb/InSe/SiO₂/Au Straddling-Type Tunneling Devices Designed As Photosensors, MOS Capacitors, and Gigahertz Bandstop Filters

In this work, amorphous InSe thin films coated with 30-160-nm-thick SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are used as an active material to fabricate multifunctional devices. The n-InSe/p-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers that are deposited onto ytterbium substrates are optically and electrically characterized. It was observed that the coating of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheets onto the surface of InSe enhances the light absorbability in the near-infrared range without remarkable altering of the bandgap. Significant increase in the steady-state photocurrent values accompanied by faster photocurrent responses resulted from the coating of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheets. Electrically, while the Yb/InSe/Au channels display tunneling Schottky barrier characteristics, the Yb/InSe/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Au channels show pn junction features. Both channels displayed metal-oxide-semiconductors (MOS) capacitance-voltage characteristics. In addition, the analyses of the current-voltage characteristics have shown that the currents in the Yb/InSe/Au and Yb/InSe/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (30 nm)/Au channel are dominated by electric field-assisted thermionic emission (tunneling) of charge carriers through barriers of widths of 18/14 and 30/16 nm under reverse-/forward-biasing conditions, respectively. Further increase in the oxide layer thickness lowered the barrier height of the devices. On the other hand, when an ac signal of low amplitude is imposed through the device channels, the conductance, capacitance, and reflection coefficient spectra displayed bandstop filter characteristics near 1.6 GHz. The microwave cutoff frequency spectra show a remarkable increase in the cutoff frequency values as a result of the coating of InSe with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheets. The features of the device assure its applicability as rectifying diodes, fast photosensors, MOS capacitors, and microwave bandstop filters.

Temperature dependent Schottky barrier characteristics of Al/n-type Si Schottky barrier diode with Au–Cu phthalocyanine interlayer

The Al/n-type Si Schottky barrier diodes (SBDs) were prepared with Au-Cu phthalocyanine (Au-CuPc) interlayers with different Au and CuPc compositional ratios, probed their temperature dependent current-voltage (I–V) and low frequency noise properties. The Schottky barrier properties like barrier height and the ideality factor are strongly temperature dependent, implying the existence of Schottky barrier inhomogeneities. The barrier inhomogeneities was elucidated using thermionic emission theory based on the assumption of Gaussian distribution of the barrier heights. Further, a divergence in the barrier heights evaluated from the I–V characteristics and Norde's method indicates a deviation of the Al/Au–CuPc/n-type Si SBDs behavior from thermionic emission. The Richardson plot evaluated with the Gaussian distribution of barrier heights method yielded Richardson constant values close to theoretical Richardson constant of n-type Si. The room temperature current noise power spectral density (SI) of the Al/Au–CuPc/n-type Si SBDs having various Au and CuPc concentrations showed a reciprocal of frequency (1/f)γ behavior having γ values near to unity. The decrease in SI and γ with increasing Au concentration in Au-CuPc interlayers was indicative of lessening barrier inhomogeneity. This was also correlated with the decrease in the value of standard deviation derived using temperature dependent I–V characteristics. Further investigations revealed that origins of 1/f noise could be associated with the fluctuations of barrier height and carrier mobility for Al/Au–CuPc/n-type Si SBDs with lower and higher Au compositions in Au-CuPc interlayers, respectively.

Band structure and Schottky barrier modulation in multilayer black phosphorene and black phosphorene/graphene heterostructure through out-of-plane strain

Density functional theory is utilized to investigate the electrical properties of multilayer black phosphorene and phosphorene/graphene heterostructure under out-of-plane strain. The effects of the number of layers and stacking order of layers on the band structure are studied. The band gap of phosphorene is inversely proportional to the number of layers, varying from 0.93 eV for single-layer to 0.15 eV for five-layer phosphorene. The results show that the direct band gap of phosphorene changes to indirect and a semiconductor to metal transition occurs in critical out-of-plane compressive strain level of 10.5%, 11% and 9% for AA, AB and AC stacked bilayer phosphorene, respectively. The critical strain depends on the band gap value and is reduced in multilayer structures. The heterostructure exhibits the characteristics of a p-type Schottky barrier which strongly depends on the strain. The p-type to n-type Schottky barrier transition occurs at the out-of-plane tensile strain of 8.5%.

Análisis de las características Corriente-Voltaje (I-V) en Barreras Schottky de Silicio (p)-Oro

The bandwidth, low cost, great storage capacity and performance are characteristics of the random Access Memories (RAM).Some kinds of RAM include ferro-random access memory (FRAM) and magnetoresistive random access memory (MRAM), the latter being of great interest to the scientific community since storage is achieved via magnetic orientation rather than electric orientation. In this paper, we analyze the effect of the application of an external magnetic field on the current-voltage (I-V) characteristics of Schottky barriers made of silicon-gold, to show the effects of magnetoresistance in dispositive semiconductors suited for use as memory storage.

Synthesis, Characterization and Fabrication of Graphene/Boron Nitride Nanosheets Heterostructure Tunneling Devices.

Various types of 2D/2D prototype devices based on graphene (G) and boron nitride nanosheets (BNNS) were fabricated to study the charge tunneling phenomenon pertinent to vertical transistors for digital and high frequency electronics. Specifically, G/BNNS/metal, G/SiO2, and G/BNNS/SiO2 heterostructures were investigated under direct current (DC-bias) conditions at room temperature. Bilayer graphene and BNNS were grown separately and transferred subsequently onto the substrates to fabricate 2D device architectures. High-resolution transmission electron microscopy confirmed the bilayer graphene structure and few layer BNNS sheets having a hexagonal B3-N3 lattice. The current vs voltage I(V) data for the G/BNNS/Metal devices show Schottky barrier characteristics with very low forward voltage drop, Fowler-Nordheim behavior, and 10−4 Ω/sq. sheet resistance. This result is ascribed to the combination of fast electron transport within graphene grains and out-of-plane tunneling in BNNS that circumvents grain boundary resistance. A theoretical model based on electron tunneling is used to qualitatively describe the behavior of the 2D G/BNNS/metal devices.

The growth of ZnO nanorods based on hydrothermal and measurement of conductivity

Zinc Oxide (ZnO) nanorods have been attracted interests as a gas molecule-catcher material in gas sensor applications. In this research, ZnO nanorods was grown on the surface of interdigitated electrode arrays substrate by using a hydrothermal method. The hydrothermal process consists of two steps, i.e., the seeding process and the growth of ZnO nanorods. The precursor material used in seeding process was Zinc Acetate Dihydrate (Zn(CH3COO)2.2H2O), while Zinc Nitrate Tetrahydrate (Zn(NO3)2.6H2O) was used as a precursor in the growth of ZnO nanorods. The sample was characterized by using scanning electron microscopy (SEM) and I-V Curve testing to determine the conductivity properties. SEM results show that ZnO nanorods has an average diameter of <100 nm. The result from the I-V curve with applied voltage in the range of 1–30 volt shows that the greater value of the applied voltage produces a decrease of the resistance value. The resistance value obtained at a given voltage of 1 volt is 7.8 kohm, while at a voltage of 30 volts is 0.5 kohm. The I-V curve profile indicates that interface between ZnO nanorods and Au-electrode shows a Schottky barrier characteristics. The gas effect with various parameters of CO gas concentrations, applied voltages and temperatures is under study.

Temperature sensor using thermally stable TiN anode GaN Schottky barrier diode for high power device application

The characteristics of GaN Schottky barrier diodes fabricated with TiN and Ni anodes were evaluated in the temperature range from 25 to 175 °C. The Schottky barrier height (ideality factor) increases (decreases) with increasing temperature for both kinds of diodes owing to the barrier height being nonhomogeneous. The GaN diode with TiN anode presents better interface quality and thermal stability is adopted for temperature sensing application. It demonstrated that the sensitivity of the TiN diode is approximately 1 mV/K and varies only slightly for all current levels.

Effects of fluorine incorporation into β-Ga2O3

β-Ga2O3 rectifiers fabricated on lightly doped epitaxial layers on bulk substrates were exposed to CF4 plasmas. This produced a significant decrease in Schottky barrier height relative to unexposed control diodes (0.68 eV compared to 1.22 eV) and degradation in ideality factor (2.95 versus 1.01 for the control diodes). High levels of F (&amp;gt;1022 cm−3) were detected in the near-surface region by Secondary Ion Mass Spectrometry. The diffusion of fluorine into the Ga2O3 was thermally activated with an activation energy of 1.24 eV. Subsequent annealing in the range 350–400 °C brought recovery of the diode characteristics and an increase in barrier height to a value larger than in the unexposed control diodes (1.36 eV). Approximately 70% of the initial F was removed from the Ga2O3 by 400 °C, with the surface outgas rate also being thermally activated with an activation energy of 1.23 eV. Very good fits to the experimental data were obtained by integrating physics of the outdiffusion mechanisms into the Florida Object Oriented Process Simulator code and assuming that the outgas rate from the surface was mediated through fluorine molecule formation. The fluorine molecule forward reaction rate had an activation energy of 1.24 eV, while the reversal rate of this reaction had an activation energy of 0.34 eV. The net carrier density in the drift region of the rectifiers decreased after CF4 exposure and annealing at 400 °C. The data are consistent with a model in which near-surface plasma-induced damage creates degraded Schottky barrier characteristics, but as the samples are annealed, this damage is removed, leaving the compensation effect of Si donors by F− ions. The barrier lowering and then enhancement are due to the interplay between surface defects and the chemical effects of the fluorine.

Significant improvement in the electrical characteristics of Schottky barrier diodes on molecularly modified Gallium Nitride surfaces

III-Nitride semiconductors face the issue of localized surface states, which causes fermi level pinning and large leakage current at the metal semiconductor interface, thereby degrading the device performance. In this work, we have demonstrated the use of a Self-Assembled Monolayer (SAM) of organic molecules to improve the electrical characteristics of Schottky barrier diodes (SBDs) on n-type Gallium Nitride (n-GaN) epitaxial films. The electrical characteristics of diodes were improved by adsorption of SAM of hydroxyl-phenyl metallated porphyrin organic molecules (Zn-TPPOH) onto the surface of n-GaN. SAM-semiconductor bonding via native oxide on the n-GaN surface was confirmed using X-ray photoelectron spectroscopy measurements. Surface morphology and surface electronic properties were characterized using atomic force microscopy and Kelvin probe force microscopy. Current-voltage characteristics of different metal (Cu, Ni) SBDs on bare n-GaN were compared with those of Cu/Zn-TPPOH/n-GaN and Ni/Zn-TPPOH/n-GaN SBDs. It was found that due to the molecular monolayer, the surface potential of n-GaN was decreased by ∼350 mV. This caused an increase in the Schottky barrier height of Cu and Ni SBDs from 1.13 eV to 1.38 eV and 1.07 eV to 1.22 eV, respectively. In addition to this, the reverse bias leakage current was reduced by 3–4 orders of magnitude for both Cu and Ni SBDs. Such a significant improvement in the electrical performance of the diodes can be very useful for better device functioning.

Morphology, stoichiometry, and crystal structure control via post-annealing for Pt–ZnO nanograin Schottky barrier interfaces

Nanointerfaces have attracted intensive research effort for advanced electronics due to their unique and tunable semiconducting properties made possible by metal-contacted oxide structures at the nanoscale. Although much work has been on the adjustment of fabrication parameters to achieve high-quality interfaces, little work has experimentally obtained the various correlations between material parameters and Schottky barrier electronic properties to accurately probe the underlying phenomenon. In this work, we investigate the control of Pt–ZnO nanograin interfaces properties by thermal annealing. Specifically, we quantitatively analyze the correlation between material parameters (such as surface morphology, crystallographic structure, and stoichiometry) and Schottky diode parameters (Schottky barrier height, ideality factor, and contact resistance). Results revealed strong dependencies of Schottky barrier characteristics on oxygen vacancies, surface roughness, grain density, d-spacing, and crystallite size. I-V-T data shows that annealing at 600 °C produces a nanograin based interface with the most rectifying diode characteristics. These dependencies, which have not been previously reported holistically, highlight the close relationship between material properties and Schottky barrier characteristics, and are instrumental for the performance optimization of nanostructured metal-semiconductor interfaces in advanced electronic devices.

Analysis of dynamic characteristics of SiC Schottky barrier diodes at high switching frequency based on junction capacitance

In this paper, we focus on relationships between dynamic characteristics and device structures of SiC Schottky barrier diodes (SBDs) to investigate their switching capabilities. A device model based on junction capacitance and thermionic emission theory is proposed. To measure the dynamic characteristics of SiC SBD, a high-frequency (10 MHz) and high-voltage (200 Vpp) wave generator is fabricated. By comparing simulated results with experimental results, it is found that the proposed model can represent the dynamic characteristics at 10 MHz and 200 °C, and the simple device model based on junction capacitance and thermionic emission theory well describes the switching behaviors of SiC SBDs at full operational temperature. The proposed device model is beneficial for designing high-power converters, at both wide temperature and wide frequency ranges.

Improved Schottky barrier characteristics for AlInN/GaN diodes by oxygen plasma treatment

In this work, the effects of oxygen plasma treatment by inductive coupled plasma on current transport of AlInN/GaN Schottky diodes were investigated. The current-voltage (I-V) results show that oxygen plasma treatment can significantly suppress reverse leakage current of the Schottky diodes by over three orders of magnitude, and meanwhile can enhance remarkably the effective barrier height and improve the ideality factor of the Schottky contact by forming a thin oxidation layer at the AlInN surface. However, I-V curve occurs a transient and recoverable reduction in current response at low forward bias. The further analysis indicates that donor-like traps related to nitrogen vacancies or their complexes induced by oxygen plasma treatment are responsible for this transient current reduction.

Vanishing Schottky Barriers in Blue Phosphorene/MXene Heterojunctions

An appropriate electrode material is crucial for two-dimensional (2D) semiconductors, where a vanishing Schottky barrier is ideal but is a great challenge. Blue phosphorene (BlueP) is a promising 2D semiconductor for electronic and optoelectronic applications. Here, we report that Zr-, Hf-, and Nb-based 2D transition metal carbides (MXenes) are ideal electrode materials for BlueP based on extensive investigations of the electronic properties and interfacial Schottky barrier characteristics of BlueP/MXene heterojunctions by first-principles calculations. Our results show that the strong interaction between BlueP and bare MXenes destroys the semiconducting character of BlueP, and thus bare MXenes are not ideal contact electrodes. With the surface functionalization of MXene, the intrinsic electronic feature of BlueP is well preserved in the BlueP/surface-engineered MXene heterojunctions. Furthermore, the interfacial Schottky barriers of the heterojunctions are affected by the terminal surface groups on MXene...

Role of interfacial oxide layer thickness and annealing temperature on structural and electronic properties of Al/Ta2O5/TiO2/Si metal–insulator–semiconductor structure

In this study, we investigated the structural and electrical properties of TiO2/Ta2O5 stacks prepared using DC reactive magnetron co-sputtering for as-deposited films and films annealed at 700 °C. X-ray diffraction studies revealed that the as-deposited films were amorphous, whereas those annealed at 700 °C were polycrystalline with mixed phases of TiO2 and β-phase Ta2O5. The presence of mixed phases of TiO2 and β-phase Ta2O5 was also confirmed by Fourier-transform infrared spectroscopy. The optical band gap of the TiO2 films was 3.46 eV for the as-deposited films and decreased to 3.35 eV with increasing Ta2O5 layer thickness on TiO2. The films annealed at 700 °C showed a decrease in band gap to 3.32 eV for TiO2, and this value further decreased to 3.15 eV with increasing Ta2O5 layer thickness on TiO2. Furthermore, we investigated the electrical properties of the sputtered TiO2/Ta2O5 stacks fabricated on a metal–insulator–semiconductor (MIS) Al/Ta2O5/TiO2/p-Si Schottky diode. We studied the variation of the fundamental Schottky barrier characteristics (ideality factor, Schottky barrier, and series resistance) for a diode prepared using reactive magnetron sputtering with TiO2/Ta2O5 as a thin insulating layer at the Al/p-type Si interface with different thicknesses at both room temperature and 700 °C. Improved electrical characteristics were observed for the annealed Al/Ta2O5/TiO2/p-Si MIS Schottky structure compared with those of the as-deposited structure.