Schottky Barrier Research Articles

Enhanced photoresponse in graphene/Al doped ZnO nanorod junction

The current study examines the performance of graphene/Al doped ZnO (ZnO:Al) heterojunction photodetectors by variation in carrier concentration of ZnO layers. This is controlled by variation of O2 percentage in growth of ZnO:Al layers produced by reactive sputtering within a small range of O2 (5–8 %). Under light, the diodes fabricated with ZnO layers deposited at 5 % O2 exhibit almost linear I–V characteristics, resulting in high photoresponsivity of around 0.08 A/W at 0 V and about 80 A/W at +3 V. Graphene/ZnO:Al junctions that are fabricated using lightly doped ZnO:Al layers deposited at ≥ 6 % O2 exhibit comparatively poorer photoresponsivity (17 A/W at +3 V) when exposed to light. The responsivity of graphene/ZnO:Al increases from 17 to 95 A W−1 as carrier concentration of ZnO layers rises from ∼1018 cm−3 to ∼5 × 1020 cm−3. Carrier concentration induced Schottky barrier height change from 0.57 to 0.75 eV which enhances the responsivity of PDs from 17 to 95 A W−1. Reactive sputtering of ZnO:Al at moderate substrate temperatures allows for technological versatility and scalability, as well as simple control over its carrier concentration. Graphene/ZnO:Al Schottky type diodes appear promising for a variety of device applications beyond photodetector applications.

Optoelectronic Reconfigurable Logic Gates Based on Two-Dimensional Vertical Field-Effect Transistors.

Optoelectronic reconfigurable logic gates are promising candidates to meet the multifunctional and energy-efficient requirements of integrated circuits. However, complex device architectures need more power and hinder multifunctional device applications. Here, we design vertical field-effect transistors (VFET) based on the two-dimensional (2D) graphene/MoS2/WSe2/graphene van der Waals heterojunction forming ohmic and Schottky contact. The modulation of the Schottky barrier via gate bias enables the device to switch between positive and negative photocurrents, which can effectively achieve optoelectronic reconfigurable logic gates (XNOR, NOR, NAND, AND, OR, and Inhibit) in a single device. Particularly, the transistor number is reduced by 75% for ("XNOR", "NOR", "NAND") and 83% for ("AND", "OR") gates compared to traditional logic circuits. This work provides a promising route for using a single device to realize optoelectronic reconfigurable logic gates, which can advance the development of high-speed, high-throughput, and intricate data processing in future optical computing applications.

650 V vertical Al0.51Ga0.49N power Schottky diodes

We report high-Al-composition (HAC) Al0.51Ga0.49N vertical power Schottky barrier diodes (SBDs) on sapphire substrates grown by metal organic chemical vapor deposition. The fabricated vertical HAC AlGaN-on-sapphire SBDs exhibit a low turn-on voltage of 1.31 V, a high on/off ratio of ∼107, a low ideality factor of 1.35, and a high breakdown voltage of 662 V.

Amorphous Exsolution of Fe3O4 Nanoparticles in SrTiO3: A Path to High Activity and Stability in Photoelectrochemical Water‐Splitting

Exsolution creates metal nanoparticles embedded within perovskite oxide matrices, promoting optimal exposure, even distribution, and robust interactions with the perovskite structure. Fe3O4, an oxidized form of Fe, is an attractive catalyst for photoelectrochemical (PEC) water‐splitting due to its strong light absorption, excellent electrical conductivity, and chemical stability. However, exsolving Fe is challenging, often requiring harsh reduction conditions that can decompose the perovskite. Herein, hybrid composites are fabricated for PEC water‐splitting by reductively annealing a solution of SrTiO3 photoanode and Fe cocatalyst precursors. In situ transmission electron microscopy reveals uniform, high‐density Fe particles exsolving from amorphous SrTiO3 films, followed by film‐crystallization at elevated temperatures. This innovative process extracts entire Fe dopants while maintaining structural stability, even at doping levels exceeding 50%. Upon air exposure, the embedded Fe particles oxidize to Fe3O4, forming a Schottky junction and enhancing light absorption. These conditions yield a high activity of 5.10 mA cm−2 at 1.23 V versus reversible hydrogen electrode (an 11.86‐fold improvement over SrTiO3) from the 30% Fe‐doped SrTiO3, with excellent stability (97% retention) over 24 h. Theoretical calculations indicate that in the amorphous state, FeO bonds weaken while TiO bonds remain strong, promoting selective exsolution. The mechanisms driving amorphous exsolution versus crystal exsolution are elucidated.

Self‐Powered and Vis‐Infrared Broadband Gr/InSe/MoTe2 Heterostructure Photodetectors with Ultra‐Fast Response and Low Dark Current

AbstractSelf‐powered photodetection devices, which meet the requirement of environmental sustainability, are widely designed by PN heterojunctions. The design of the semiconductor/metal interface is vital in PN‐junction devices. In particular, the elevated potential barrier at the metal/semiconductor interface impedes efficient carrier transport. Therefore, optimizing the semiconductor/metal interface for the PN junction, either by reducing the interface barrier or leveraging the built‐in electric field within the Schottky junction, holds significant importance in enhancing the performance of PN‐junction devices. In this study, an InSe/MoTe2 Type‐II PN heterojunction photodetector is constructed, with graphene (Gr) and gold (Au) serving as electrodes in contact with InSe and MoTe2, respectively. Benefiting from the reduced barrier in Au/InSe interfaces and the built‐in electric field formed at the InSe/MoTe2 and MoTe2/Au interfaces in the same direction, the device achieves an ultra‐fast photoresponse speed of 14 µs and an ultra‐low dark current of 8.5 × 10⁻¹⁴ A at zero bias. Furthermore, the device exhibits a remarkable light on/off ratio up to 105 and achieves broad‐spectrum photodetection ranging from the visible to infrared wavelength. This research highlights the enormous potential of the Gr/InSe/MoTe2 van der Waals heterostructure in the realms of self‐powered photodetection, imaging, and optical communication.

The relationship of voltage variations in the third quadrant and the Schottky area ratios in a 4H-SiC SBD-embedded MOSFET

Based on the measured and the TCAD simulation results, this paper provides a detailed description of the third quadrant characteristics of the Schottky barrier diode (SBD) embedded MOSFETs with different Schottky area ratios of 2.6 %, 5.3 %, and 14.7 %. As the Schottky area ratio increases, the shift of the third quadrant turn-on voltages of the MOSFETs influenced by the gate voltage decreases. The shift rates in the conventional MOSFET and SBD-embedded MOSFETs are from 57.2 % to 0 % when Vgs changes from 0 V to −4 V. The shift rate becomes 0 % when the Schottky area ratio is larger than 5.3 %. Simultaneously, the TCAD simulation results and the measured results indicate that the SBD-embedded MOSFETs can effectively suppress the conduction of the low barrier diode and the body diode.Furthermore, the SPICE models were built to explain the physics mechanisms. The fitting error between the measured and fitting results is as low as 1.3 % among the models with the different Schottky area ratios.

Analysis of Current-Voltage Properties of Schottky Diode with TiO2 Interlayer Prepared by RF Magnetron Sputtering

The presented study focuses on investigating the electrical behaviour of Metal-Insulator-Semiconductor (MIS) type Schottky barrier diodes based on titanium oxide (TiO2). A MIS-type Al/TiO2/p-Si Schottky diode structure was fabricated by depositing a TiO2 metal oxide thin film as an interlayer on p-type silicon using the Radio Frequency Magnetron Sputtering technique. The electrical performance of this fabricated structure was evaluated through current-voltage (I-V) measurements conducted in a dark environment at ±5 V and room temperature. These measurements enabled the determination of key Schottky diode parameters including ideality factor (n), barrier height (Φb), and saturation current (Io) using both the Thermionic Emission (TE) method and the Cheung method. Utilizing the TE method, approximate values for Φb, n, and Io parameters were calculated as 0.59 eV, 4.07, and 2.78E-06 A, respectively. Meanwhile, employing Cheung’s method yielded approximate values of Φb and n parameters as 0.39 eV (H(I) vs I) and 4.39 (dV/dln(I) vs I), respectively. The analysis indicates that the developed Schottky diode functions as a rectifier diode, demonstrating typical diode characteristics. Furthermore, a comparison of numerous devices reported in the literature was conducted based on TiO2 preparation methods against the parameters of the TiO2/p-Si host device.

Material Transfer and Contact Optimization in MoS2 Nanotube Devices

While the promise of clean and defect‐free nanotubes as quantum electronic devices is obvious, ranging from strong spin–orbit interaction to intrinsic superconductivity, device fabrication still poses considerable challenges. Deterministic transfer of transition metal dichalcogenide nanomaterials and transparent contacts to the nanomaterials are nowadays highly active topics of research, both with fundamental research and applications in mind. Contamination from transport agents as well as surface adsorbates and surface charges play a critical role for device performance. Many techniques have been proposed to address these topics for transition metal dichalcogenides in general. Herein, their usage for the transfer‐based fabrication of nanotube devices is analyzed. Further, different contact materials are compared in order to avoid the formation of a Schottky barrier.

Spectroscopic Analysis of Electrical Phenomena and Oxygen Vacancy Generation for Self-Aligned Fully Solution-Processed Oxide Thin-Film Transistors.

This work unveils critical insights through spectroscopic analysis highlighting electrical phenomena and oxygen vacancy generation in self-aligned fully solution-processed oxide thin-film transistors (TFTs). Ar inductively coupled plasma treatment was conducted to fabricate an amorphous indium zinc oxide (a-InZnO) TFT in a self-aligned process. Results showed that the Ar plasma-activated a-InZnO regions became conductive, which means that a homogeneous layer can act as both channel and electrode in the device. Several techniques were employed to probe specific aspects of the source-drain-channel interface in the fully solution-processed TFTs. X-ray absorption near-edge structure and Extended X-ray absorption fine structure were conducted to investigate the existence of oxygen vacancies, which is the main driving factor in inducing a conductive region. X-ray photoelectron spectroscopy was also used to explain the oxygen refilling mechanism. Ultraviolet Photoelectron Spectroscopy was conducted to analyze the valence band maximum and work function. Integration of these results facilitated the construction of the energy band diagram at the interface, wherein a Schottky barrier height of ∼0.37 eV was observed. By leveraging these techniques, insights into the electronic properties and performance of next-generation transistors are gained, enabling their future widespread adoption.

Demonstration of aluminum nitride metal oxide semiconductor field effect transistor on sapphire substrate

Abstract Aluminum nitride (AlN) is a promising ultrawide bandgap material with significant advantages for power electronics and optoelectronic applications due to its high breakdown voltage, mobility, and thermal conductivity. AlN Schottky barrier diodes and metal semiconductor field effect transistors have shown potential but are limited by issues such as high off-state leakage current and complex structures to achieve ohmic contacts. To address these challenges, we report on the fabrication and characterization of an AlN metal oxide semiconductor field effect transistor (MOSFET) with a recessed gate structure. The source and drain contacts were fabricated on n-doped AlN epitaxy using Ti-based contacts with a Ti/Al/Ti/Au metal stack. To evaluate the performance of these contacts, a circular transmission line model was employed, and contacts were annealed at various temperatures ranging from 750 °C to 950 °C in a nitrogen ambient. Our results reveal that unannealed Ti-based contacts on AlN showed no current conduction. However, annealing these contacts at 950 °C for 30 s significantly reduced the specific contact resistance to 0.148 Ω·cm2, achieving an ∼80% reduction compared to samples annealed at 750 °C. Utilizing these optimized contact conditions, we fabricated, to the best of our knowledge, the first AlN MOSFET. The fabricated AlN MOSFET exhibits a threshold voltage of −10.91 V, an effective mobility of 2.95 cm2 V−1 s−1, an on–off current ratio spanning two orders of magnitude, and a reverse breakdown voltage of approximately ∼250 V in air without a field plate.

P-type Schottky-barrier-free contact to MoS2 via layer-number-assisted interface engineering

Bilayer and few-layer MoS2 show intrinsically higher electronic quality and substantially improved device performance than monolayer, and high-quality MoS2 wafers with controlled layer number have been grown. In addition, MoS2 has different polymorphs such as the semiconducting H phase and semimetallic distorted T (dT) phase, and vertically stacked dT-/H-MoS2 metal-semiconductor junctions (MSJs) have been synthesized. However, the contact mechanism of dT-/H (few layer)-MoS2 MSJs remains to be elucidated, and p-type ohmic contact to MoS2 is difficult to realize due to the high ionization energy of MoS2. In the current work, we reveal a mechanism of two-dimensional (2D) semiconductors (2DSCs) layer-number-assisted metal-semiconductor (SC) interface engineering for Schottky barrier height (SBH) reduction and p-type ohmic contact is achieved based on this mechanism; 2DSCs here mean H (few layer)-MoS2 and metal-SC interfaces are the dT-/H-MoS2 interfaces with increasing 2DSC layers. Specifically speaking, the mechanism is as follows: (1) two competing effects coexist, namely, the interface dipole (ΔV) at the metal-SC interface and the quasibonding (QB) between all adjacent layers, with ΔV (QB) increasing (decreasing) SBH; (2) the effect of QB beats ΔV and hence the overall effect is decreasing SBH at the metal-SC interface; and (3) the SBH reduction effect increases with increasing 2DSC layers. The mechanism of 2DSC layer-number-assisted metal-SC interface engineering should apply also for other 2DSCs with a suitable metal and hence our current work paves an avenue for ohmic contact to few-layer 2DSCs by the accumulated interlayer QBs that widely present in 2DSCs. Published by the American Physical Society 2024

Device simulation study of multilayer MoS2 Schottky barrier field-effect transistors

Molybdenum disulfide (MoS2) is a representative two-dimensional layered transition-metal dichalcogenide semiconductor. Layer-number-dependent electronic properties are attractive in the development of nanomaterial-based electronics for a wide range of applications including sensors, switches, and amplifiers. MoS2field-effect transistors (FETs) have been studied as promising future nanoelectronic devices with desirable features of atomic-level thickness and high electrical properties. When a naturallyn-doped MoS2is contacted with metals, a strong Fermi-level pinning effect adjusts a Schottky barrier and influences its electronic characteristics significantly. In this study, we investigate multilayer MoS2Schottky barrier FETs (SBFETs), emphasizing the metal-contact impact on device performance via computational device modeling. We find thatp-type MoS2SBFETs may be built with appropriate metals and gate voltage control. Furthermore, we propose ambipolar multilayer MoS2SBFETs with asymmetric metal electrodes, which exhibit gate-voltage dependent ambipolar transport behavior through optimizing metal contacts in MoS2device. Introducing a dual-split gate geometry, the MoS2SBFETs can further operate in four distinct configurations:p - p,n - n,p - n, andn - p. Electrical characteristics are calculated, and improved performance of a high rectification ratio can be feasible as an attractive feature for efficient electrical and photonic devices.

Micropyramidal Si Photonics–A Versatile Platform for Detector and Emitter Applications

AbstractAnisotropic wet etching of silicon (Si) has been known for decades, but the extraordinary capabilities of this technology to provide highly ordered microphotonic arrays have received limited attention in previous studies. It is shown that these capabilities include: i) a unique self‐terminating etching nature − crucial for achieving uniform arrays over centimeter‐scale wafers, ii) an extraordinary smoothness of the slow‐etching (111) planes, and iii) a precise geometry control including the extent micropyramids or micropyramidal voids are truncated. The combination of these properties transforms this technology into a versatile platform for novel detector and emitter applications in Si photonics. The optical properties of such arrays are studied by finite‐difference time‐domain modeling in two realms represented by different boundary conditions (BCs). Periodic BCs result in Talbot self‐images experimentally observed in this work. Perfectly matched layer BCs describe mesoscale interference effects resulting in the subwavelength focusing properties of micropyramids. Enhancements in the performance of mid‐wave infrared (MWIR) focal plane arrays are demonstrated by monolithic integration of Si micropyramids with silicon‐platinum silicide Schottky barrier photodetectors. Finally, it is shown that Si micropyramidal arrays can be used to enhance light extraction and directionality of quantum sources and infrared scene projectors.

Ni/n-Si Schottky junction: Self-biased infrared photodetection via hot carrier photoemission

Internal photoemission-based hot electron generation at metal-semiconductor junctions holds significant potential for silicon-based sub-bandgap NIR photodetectors. In this work, we designed a simple nickel-silicon Schottky junction using the pulsed laser deposition technique and performed both experimental and theoretical analyses. To reduce the complexity of fabrication and lower costs, we used a planar nickel thin film on top of n-type silicon. The thickness of the nickel thin film was optimized to improve absorption and hot electron generation near the Ni/Si interface. We measured and calculated reflectance using the transfer matrix approach to quantify the effect of thickness on EQE. We also calculated the thickness-dependent absorption profile to estimate hot electron production near the junction. The current-voltage characterization of Ni/n-Si Schottky photodetector was investigated under the dark conditions as well under 1200 nm and 1300 nm light illumination. Under self-bias conditions, a photodiode with a 12 nm Ni thickness exhibits responsivity of 0.124 mA/W and 0.069 mA/W under illumination from 1200 nm and 1300 nm LED light, respectively. Furthermore, we used a comprehensive theoretical model to quantify the planar Ni/Si hot carrier generation and emission efficiency. and experimentally validated the calculated EQEs with the fabricated device. We believe the proposed complementary metal-oxide-semiconductor-compatible and simply structured Ni/Si Schottky photodetector will have potential applications in the silicon-based optoelectronics market.

Next-Generation Self-Powered Photodetectors using 2D Bismuth Oxide Selenide Crystals.

The concept of self-powered photodetectors has attracted significant attention due to their versatile applications in areas such as intelligent systems and hazardous substance detection. Among these, p-n junction and Schottky junction photodetectors are the most widely studied types; however, their fabrication processes are often complex and costly. To overcome these challenges, we focused on the emerging self-powered, ultrasensitive photodetector platform based on photoelectrochemical (PEC) principles. This platform leverages the unique properties of the emerging material bismuth oxide selenide (Bi2O2Se), which features a wide bandgap (∼2 eV) and a high absorption coefficient. We utilized chemical exfoliation to obtain thin layers of Bi2O2Se, enabling highly efficient photodetection. The device characterization demonstrated impressive performance metrics, including a responsivity of 97.1 μA W-1 and a specific detectivity of 2 × 108 cm Hz 1/2 W-1. The PEC photodetector also exhibits broad-spectrum sensitivity, from blue to infrared wavelengths, and features an ultrafast response time of ∼82 ms and a recovery time of ∼86 ms, highlighting its practical potential. Moreover, these self-powered photodetectors show excellent stability in electrochemical environments, positioning them promising candidates for integration into future high-efficiency devices.

Construction of LDH-derived CoNiP modified W/Z-CdS homojunction for improved photocatalytic hydrogen evolution: Achieving broad solar light response and multiple phases charge transfer

Heterojunction engineering represents a robust strategy for accelerating carrier transfer, thereby enhancing the activity of photocatalytic hydrogen evolution. In this work, a series of innovative CoNiP@W/Z-CdS heterojunctions were prepared for the purpose of investigating the photocatalytic hydrogen evolution activity under visible light-driven. To achieve high efficiency, lamellar CoNiP was first synthesized through the phosphatisation of CoNi LDH precursor. Subsequently, the W/Z-CdS homojunction was in-situ grown on the CoNiP via the hydrothermal method, resulting in the formation of the CoNiP@W/Z-CdS homojunction/heterojunction. The hydrogen evolution rate of 3% CoNiP@W/Z-CdS composite reaches 60.6 mmol/g/h, which is 3.6 times, 7.0 times and 11.9 times higher than that of W/Z-CdS, W-CdS and Z-CdS, respectively. The enhanced photocatalytic performance of 3% CoNiP@W/Z-CdS can be attributed to the introduction of an ultra-thin CoNiP bimetallic phosphide as cocatalyst, which increases the specific surface area to provide a large number of active sites for the catalytic reaction, and broadens the absorption range of sunlight. In particular, the synergistic effect between homojunction and Schottky junction in 3% CoNiP@W/Z-CdS further accelerates separation and migration rate of double interfacial carriers, improving photocatalytic H2 rate. This work offers a new perspective for the rational design of three-phase binary photocatalysts with high activity and stability.

Design and Optimization of High Performance Multi-Step Separated Trench 4H-SiC JBS Diode

In this paper, a novel 3300 V/40 A 4H-SiC junction barrier Schottky diode (JBS) with a multi-step separated trench (MST) structure is proposed and thoroughly investigated using TCAD simulations. The results show that the introduction of MST expands the Schottky contact area, resulting in a decrease in the forward voltage drop. Furthermore, the combination of the deep P+ shielded region and the central P+ region effectively reduces the leakage current, leading to a 43.7% increase in the blocking voltage compared to conventional 4H-SiC JBS. The effects of the step depth (ds) and the width of the central P+ region (wm) on the device performance are analyzed in depth. In addition, a multi-step trenched linearly graded field-limiting rings (MTLG-FLR) termination ensures a more uniform electric field distribution, and the terminal protection efficiency reaches up to 90%, which further enhances the reliability of the terminal structure.

All‐Electronic Memristor Based on Charge Carrier Confinement in Bulk Semiconductor of Metal–Semiconductor–Metal Structure

AbstractMemristors have gained significant attention in recent years due to their potential applications in computing and memory technology by offering higher performance, lower power consumption, and increased storage capacity. In this paper, a new type of volatile memristor is presented by analyzing the dynamic behavior of charge carriers within a metal–semiconductor–metal (MSM) structure. It is shown that an all‐electronic memristor is achieved through the confinement of majority charge carriers within the bulk semiconductor by the favor of high barrier Schottky contacts. The findings reveal a remarkable current offset between forward and backward scans, along with exceptional current pulse consistency with a tunable current level using pulse frequency. These characteristics greatly simplify the process of designing electrical circuits incorporating this memristor variant. Furthermore, this research paves the way for the development of crystalline semiconductor‐based memristors. While various semiconductors with controllable doping densities can be considered as potential candidates for this type of memristor, the calculations using silicon demonstrate the integration of this semiconductor with the current technology holds significant promise for two terminal memristors.

Fast switching Ga2O3 Schottky barrier power diode with beveled-mesa and BaTiO3 field plate edge termination

Power devices rely on ideal edge termination to suppress the electric field crowding and avoid premature breakdown before the material's critical field is reached. In this work, a hybrid electric field management configuration, featuring the combination of beveled-mesa (BM) termination and high-k oxide BaTiO3 field plate (FP), was implemented in Ga2O3 Schottky barrier diodes (SBDs). This BMFP-SBD realizes a breakdown voltage (BV) of 1.7 kV with extremely low reverse leakage current, outperforming the BM terminated SBD with BV of 0.64 kV and bare SBD with BV of 0.22 kV. Based on the temperature-dependent reverse characteristics, the dominant leakage mechanism transforms from Poole–Frenkel (P–F) emission in BM-SBD to variable-range-hopping (VRH) in BMFP-SBD at high bias. In particular, under switching conditions of di/dt up to 420 A/μs, the BMFP-SBD exhibits superior dynamic switching characteristics with a short reverse recovery time of 10.1 ns, which are comparable with those in advanced commercial SiC SBDs. These findings underscore the potential of Ga2O3 SBD enabled by BM and high-k FP edge termination for high-speed and high-voltage power electronics applications.

Comprehensive device modeling for AlGaN/GaN based Schottky barrier diodes with beveled p-GaN termination to control electric field

In this article, we have systematically investigated the impact of different structural parameters on the electrical characteristics for AlGaN/GaN based Schottky barrier diodes (SBDs) with beveled p-GaN termination by using TCAD simulation tools. The p-GaN termination can decrease the electric field at the Schottky contact region, thereby suppressing the electrical field magnitude in the Schottky contact region. Then, the breakdown voltage can be enhanced without remarkably sacrificing the forward conduction characteristics. However, in spite of the reduced electric field magnitude in the Schottky contact region, the electric field will possess the peak value at the edge of p-GaN termination. Therefore, the premature breakdown can occur when the electric field therein reaches critical value. Hence, we have comprehensively manipulated the electric field distributions by designing different p-GaN terminations and detailed optimization strategy for the AlGaN/GaN based Schottky barrier diodes has been conducted. Moreover, we find that the strong electric field at the p-GaN termination edge can be reduced by using beveled p-GaN termination, which can extend the electric potential into the bulk GaN region. With the developed defected-related physical models, we also find that the p-GaN termination suppress the capture and release process for the carriers by defects, which improves the dynamic characteristics for the proposed devices.