Lateral Schottky Research Articles

Recessed AlGaN/GaN Schottky Barrier Diodes With TiN and NiN Dual Anodes

High-performance AlGaN/GaN lateral Schottky barrier diodes (SBDs) with recess structure and dual metal nitride anodes were demonstrated. With high work-function and nonrecess structure, a NiN anode enhances the breakdown voltage (BV), while a TiN anode reduces the turn-on voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ) due to its low work-function and contact to the two-dimensional electron gas (2DEG) layer directly on a recess structure. As the length of the NiN anode ( L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) on the nonrecess region decreases from 75 to 3 μm, V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> is reduced from 0.56 to 0.30 V, while the reverse leakage current slightly increases from 3 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> to 2 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the bias of -10 V. The lateral AlGaN/GaN SBD with a L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> of 3 μm at a distance of cathode-anode ( L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</sub> ) of 20 μm achieves a high BV of 1.62 kV, an ultralow V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> of 0.30 V and a small capacitance of 6.0 pF at zero bias with little degradation on ON-resistance, indicating superior potential application in high-frequency and high-power devices.

Monolithic Integrated Normally OFF GaN Power Device With Antiparallel Lateral Schottky Barrier Controlled Schottky Rectifier

Integration of an enhancement-mode (E-mode) metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) with a high-performance lateral Schottky barrier controlled Schottky (LSBS) rectifier in a compact layout is fabricated on an ultrathin-barrier AlGaN/GaN heterostructure grown on Si substrate. The state-of-the-art reverse conduction voltage ( ${V}_{{\text {rev}}}$ ) of 0.455 V was achieved in the monolithic integrated E-mode power device with a threshold voltage of 1.55 V. ${V}_{{\text {rev}}}$ exhibited a tiny temperature variation of 0.66% from 0 °C to 150 °C compared with that of 157% for the controlled E-mode HEMT.

Optoelectronic properties of laser-beam-patterned few-layer lateral MoS2 Schottky junctions

Atomically thin (or few-layer) two-dimensional transition metal dichalcogenide (TMDC) materials have various unique optoelectronic properties, which bring advantages for application to flexible solar cells and photodetectors, by bandgap engineering via van der Waals hybridization. TMDCs have crystal phase structures, such as the 2H semiconducting phase and the 1T (or 1T′) metallic phase. Recently, we demonstrated the creation of few-atom-layer 1T-metal/2H-semiconductor molybdenum disulphide (MoS2) lateral Schottky junctions by using electron beam (EB) irradiation and revealed their unique optoelectronic properties. However, the 1T phase is metastable, whereas the 1T′ phase is more stable and useful for various applications. Here, we create a few-layer 1T′-metal phase MoS2 by laser beam irradiation, which is a simpler, convenient, and low-cost method compared to EB irradiation. We observe unique optoelectronic features of the few-atom-layer 1T′-metal/2H-semiconductor lateral Schottky junctions in reverse bias voltage regions, such as an effective barrier height of ∼0.15 eV, highly efficient photogeneration ratios (&amp;gt;20%), and high sensitivity to photoirradiation angles without degradation for one month. These properties show great promise for application to highly efficient, flexible, and semitransparent photodetectors and solar cells with long-term reliability.

Ohmic contacts of monolayer Tl2O field-effect transistors

Monolayer (ML) Tl2O, as a newly discovered metal-shrouded two-dimensional semiconductor with an appropriate bandgap and high carrier mobility, is a promising candidate as the channel materials for the next-generation field-effect transistors (FETs). Using ab initio electronic structure calculation and quantum transport simulation, the contact properties of ML Tl2O–metal interfaces based on FET are comprehensively investigated with Au, Sc, Tl, Ni, graphene, Ti2C, Ti2CF2, and Ti2C(OH)2 electrodes. ML Tl2O undergoes metallization with Au, Sc, Tl, Ni, and Ti2C, while it forms van der Waals-type contact with graphene, Ti2CF2, and Ti2C(OH)2. An n-type lateral Schottky contact is formed with Ni, Au, Sc, and Ti2C electrodes with the electron Schottky barrier height (SBH) of 0.25, 0.27, 0.27, and 0.36 eV, respectively, while a p-type lateral Schottky contact is formed with graphene electrode with the hole SBH of 0.10 eV. Surprisingly, a desired n-type Ohmic contact arises with Tl and Ti2C(OH)2 electrodes and a desired p-type Ohmic contact arises with Ti2CF2 electrode. The study not only provides a deep understanding of the interfacial properties of the ML Tl2O FETs but also reveals a versatile approach to realize both n- and p-type Ohmic contact for the ML Tl2O FETs.

Design of MXene contacts for high-performance WS2 transistors

Achieving low-resistance contact is crucial for enhancing the performances of nanoelectronic devices. To find high-performance WS2 transistors, we systematically investigated the interfacial properties of monolayer WS2 in contact with a series of MXenes (Ti2C, V2C, Cr2C, Zr2C, Hf3C2, and Ti3C2) using first-principles calculations. Analyses of the interface structure, effective potential, electron localization function, energy bands, and density of states of the MXene top contacts with monolayer WS2 indicated that Ti2C, Zr2C, Hf3C2, and Ti3C2 couple strongly with WS2, leading to the metallization of monolayer WS2 and the formation of ideal Ohmic contacts in the vertical direction. To further evaluate the performances of the WS2/MXene transistors, the quantum transport properties were simulated using the nonequilibrium Green’s function method. The results indicated that the WS2 transistors with Zr2C and Hf3C2 electrodes have small lateral Schottky barrier heights of 0 and 0.08 eV, respectively, implying the formation of Ohmic and quasi-Ohmic contacts in WS2/Zr2C and WS2/Hf3C2. It means that low-resistance contacts can be achieved at WS2/Zr2C and WS2/Hf3C2 systems, indicating that Zr2C and Hf3C2 are promising electrode for monolayer WS2 to form high-performance transistors. These findings provide vital insights for the design of high-performance nanoelectronic devices based on two-dimensional materials.

Electrical Contact between an Ultrathin Topological Dirac Semimetal and a Two-Dimensional Material

Ultrathin films of topological Dirac semimetal, Na$_3$Bi, has recently been revealed as an unusual electronic materials with field-tunable topological phases. Here we investigate the electronic and transport properties of ultrathin Na$_3$Bi as an electrical contact to two-dimensional (2D) metal, i.e. graphene, and 2D semiconductor, i.e. MoS$_2$ and WS$_2$ monolayers. Using combined first-principle density functional theory and nonequilibrium Green's function simulation, we show that the electrical coupling between Na$_3$Bi bilayer thin film and graphene results in a notable interlayer charge transfer, thus inducing sizable $n$-type doping in the Na$_3$Bi/graphene heterostructures. In the case of MoS$_2$ and WS$_2$ monolayers, the lateral Schottky transport barrier is significantly lower than many commonly studied bulk metals, thus unraveling Na$_3$Bi bilayer as a high-efficiency electrical contact material for 2D semiconductors. These findings opens up an avenue of utilizing topological semimetal thin film as electrical contact to 2D materials, and further expands the family of 2D heterostructure devices into the realm of topological materials.

Epitaxial diamond on Ir/ SrTiO3/Si (001): From sequential material characterizations to fabrication of lateral Schottky diodes

Advanced characterizations with combined analytical tools were carried out at the different stages of diamond heteroepitaxy on Ir/STO/Si (001) substrates. HRTEM and STEM-EELS revealed the presence of epitaxial nanometric diamond crystals after bias enhanced nucleation. UV Raman allowed estimating the diamond film quality and its strain at the early stages of heteroepitaxial growth. The crystalline structure and the strain within thick heteroepitaxial films were determined by XRD and CL investigations. A CL study of the cross-section provided the mapping of the dislocation network along the growth direction. Measurements performed on lateral Schottky diodes fabricated on a thick diamond film showed an excellent reproducibility on the substrate with a Schottky barrier height in good agreement with those obtained on homoepitaxial layers.

The Influence of Anode Trench Geometries on Electrical Properties of AlGaN/GaN Schottky Barrier Diodes

AlGaN/GaN lateral Schottky barrier diodes (SBDs) with three different anode geometries (stripe, circular, and the conventional plane one) and different rows of anode trenches are fabricated and electrically characterized to study the influence of anode trench geometries. The SBDs with anode trenches exhibit the lower on-state resistance (RON) than that with the conventional plane one. It can be explained that the anode trenches made the Schottky metal directly contact to the 2DEG at the sidewall of the AlGaN/GaN interface, removing the AlGaN barrier layer in the conventional plane anode. In addition, the RON of the SBDs with circular trenches is smaller than that of the SBDs with stripe ones. Furthermore, the RON decreases with the increasing rows of anode trenches, which can be attributed to the increased contact area between the Schottky metal and the 2DEG. For the reverse characteristics, the anode trenches do not lead to performance degradation. The fabricated devices exhibit the low reverse current (IR, IR &lt; 1 μA/mm), and the breakdown voltage (VBK) remains unchanged with different anode geometries.

The effect of edge-terminated structure for lateral AlGaN/GaN Schottky barrier diodes with gated ohmic anode

We have investigated the effect of an edge-terminated structure in the anode of a gated ohmic anode AlGaN/GaN lateral Schottky Barrier Diode (SBD) device. The edge-terminated structure in the anode serves as a kind of field plate, which suppresses a reverse leakage current and improves a switching characteristic by reducing trapping effect at the active region. According to our two-dimensional simulation results, the electric field concentration near the edge of the anode was relatively reduced by the edge-terminated structure. For the fabricated devices, it was exhibited that the diode with proposed structure has lower reverse leakage current density without degradation of the forward current density, compared to the diode without the edge-terminated structure. In addition, the pulse response degradation was significantly improved from 16 to 3.5% at the forward voltage of 1.5 V when the reverse voltage of −100 V was applied.

Investigation of nitride lateral Schottky barrier diodes based on InGaN channel heterostructures

In this work, nitride lateral Schottky barrier diodes (SBDs) are manufactured on InGaN channel heterostructures, and the superior performances are investigated in detail. Due to the decent electron confinement of InGaN channel heterostructures, a high current on/off ratio of 107 is achieved for the SBDs. In addition, the turn-on voltage (Von) of lateral InGaN channel SBDs is as low as 0.55 V owing to the employment of a low work function tungsten (W) anode. Particularly, the excellent thermal stability of the InGaN channel SBDs is demonstrated. At 150 °C, the maximum forward anode current (Imax) reaches 63% of the value at room temperature, and the reverse leakage current only degenerates by 3.5 times compared to the room temperature value, which are evidently better than the results of traditional GaN channel SBDs. Moreover, the high linearity of InGaN channel SBDs at both room temperature and elevated temperature is revealed. These results demonstrate the great promise of lateral InGaN channel SBDs in high power and wideband electronics fields in the future.

Planar Direction‐Dependent Interfacial Properties in Monolayer In2Se3–Metal Contacts

2D semiconductor materials are promising channel materials in the next generation of field‐effect transistors (FETs). Recently, 2D In2Se3 has been fabricated and predicted to present planar direction‐dependent electrical properties. Herein, ab initio quantum transport simulations are used to explore the interfacial properties between monolayer (ML) In2Se3 and a series of common metal electrodes in a FET. By reversing the planar direction of ML In2Se3, different lateral interfacial properties are obtained: A highly desirable n‐type ohmic contact is shaped between Au and up‐directed ML In2Se3; however, a p‐type Schottky contact appears when the direction is switched. In addition, Ag can generate desirable lateral n‐type ohmic contact with both the directions of ML In2Se3. A reversion from n‐ to p‐type lateral Schottky contact occurs in both In and Sc when the direction switches from up to down. Down‐directed ML In2Se3 is dynamically unstable with the Pt and transforms into up‐direction to form a p‐type ohmic contact. The average pinning factor is 0.12 and 0.09 for up‐and down‐directed ML In2Se3, respectively, implying a strong Fermi‐level pinning. Therefore, the planar direction‐dependent interfacial properties of ML In2Se3–metal contacts are understood deeply, which can be exploited for the ML In2Se3 FET devices.

A &gt; 3 kV/2.94 m $\Omega\cdot$ cm2 and Low Leakage Current With Low Turn-On Voltage Lateral GaN Schottky Barrier Diode on Silicon Substrate With Anode Engineering Technique

In this letter, we report on demonstrating high-performance lateral GaN Schottky barrier diode (SBD) on silicon substrate with low turn-on voltage ( $\text{V}_{\mathbf {on}}$ ), high breakdown voltage (BV) with low reverse leakage current ( $\text{I}_{\mathbf {R}}$ ), and high power figure of merit (P-FOM) through anode engineering technique. Lateral GaN SBD with anode-cathode distance ( $\text{L}_{\mathbf {AC}}$ ) of $25~\mu \text{m}$ demonstrates a $\text{V}_{\mathbf {on}} =0.38$ V, a BV of >3 kV at a $\text{I}_{\mathbf {R}}$ of $10\mu \text{A}$ /mm and differential specific ON-resistance ( $\text{R}_{\mathbf {on,sp}}$ ) of 2.94 $\text{m}\Omega ~\cdot $ cm2, yielding a high P-FOM of more than 3 GW/cm2. To the best of our knowledge, this P-FOM is the highest value among all the GaN SBDs on any substrates. Combining with 5 A forward current ( $\text{I}_{\mathbf {F}}$ ) and reverse BV >2 kV of a large periphery device with perimeter of 20 mm, GaN SBD with anode engineering technique shows its great promise for next generation power electronics.

Lateral GaN Schottky Barrier Diode for Wireless High-Power Transfer Application With High RF/DC Conversion Efficiency: From Circuit Construction and Device Technologies to System Demonstration

In this article, we have carried out a comprehensive study on the wireless power transfer (WPT) concept from the rectifier circuit construction and state-of-art GaN Schottky barrier diode (SBD) device technology to the WPT system demonstration. Benefited from the wide bandgap, high mobility, and saturation velocity of the gallium nitride (GaN) two-dimensional electron gas, engineered lateral GaN SBD with low turn-ON voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) of 0.47 V, ON-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) of 4 Ω, breakdown voltage of 170 V, and junction capacitance (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ) of 0.32 pF at 0 V bias are achieved, which satisfy the fundamental requirements for microwave power rectification. After incorporating the high-performance GaN SBD into the optimized rectifier circuit, high radio frequency (RF)/dc conversion efficiency of 79% is achieved, and the input power of per single GaN SBD is increased by 10X when compared with that of a commercially available silicon (Si) SBD at the same efficiency of 50% and frequency of 2.45 GHz. Based on the rectifier circuit, a microwave power transfer system is constructed with 400 light emitting diodes lighted up, verifying the great promise of adopting high-power GaN SBD for the wireless high-power transfer as an alternative energy-harvesting technique for future WPT application.

A 5.8-GHz High-Power and High-Efficiency Rectifier Circuit With Lateral GaN Schottky Diode for Wireless Power Transfer

In this letter, we propose to implement a microwave lateral GaN Schottky barrier diode (SBD) in a designed 5.8-GHz rectifier circuit for future high-power and high-efficiency wireless power transfer. The low-pressure chemical vapor deposition SiN-passivated lateral GaN SBD demonstrates a low turn- on voltage of 0.38 V, a low on -resistance of 4.5 Ω, a low junction capacitance of 0.32 pF at 0-V bias, and a high breakdown voltage of 164 V, which are essentials for a high-efficiency and high-power rectifying application. By incorporating this lateral GaN SBD in a well-designed 5.8-GHz rectifier circuit, an unprecedented combination of high efficiency and high power is achieved simultaneously. The rectifier circuit demonstrates a high RF/dc conversion efficiency ( η RF/DC) of 71 ± 4.5% with an input power ( P in) of 2.5 W and η RF/DC = 50 ± 4.5% with P in = 6.4 W per single diode, showing the great promise of embracing lateral GaN SBD for future wireless high-power transfer application.

High-Performance Metal-Organic Chemical Vapor Deposition Grown $\varepsilon$ -Ga2O3 Solar-Blind Photodetector With Asymmetric Schottky Electrodes

In this letter we present a high performance $\varepsilon $ -Ga2O3 solar-blind photodetector (SBPD) with asymmetric Schottky electrodes. The $\varepsilon $ -Ga2O3 films were heteroepitaxially grown on ${c}$ -plane sapphire by metal-organic chemical vapor deposition (MOCVD). The SBPDs were fabricated in the form of lateral interdigitated Schottky electrodes composed of a Pt/Ti/Au metal stack and a Ti/Au metal stack. The SBPD shows a rectification ratio of ~ 102 with low dark current of 25 pA at ${V} = {6}$ V. A high photo-to-dark-current ratio of ${5.7}\boldsymbol {\times }{10}^{{4}}$ under 254 nm light illumination was measured. Furthermore, the SBPD exhibits an ultrahigh detectivity and external quantum efficiency of ${4.2}\boldsymbol {\times }{10}^{{14}}$ Jones and ${4.1}\boldsymbol \,\,{\times }\,\,{10}^{{4}}$ %, respectively. Most importantly, the SBPD possesses an ultrahigh responsivity of 84 A/W with a fast response speed of 100 ms, suggesting the promise of $\varepsilon$ -Ga2O3 in the future photodetector applications.

Width dependent rectifying behavior in Schottky heterojunction based on black phosphorene

Lateral Schottky heterojunctions are designed by metallic black phosphorene with S modified edge and semiconducting black phosphorene with H modified edge. The first principles calculations show asymmetrical current–voltage characteristics for designed devices exhibiting a rectifying behavior. The reduced rectifying ratios are found at the bias from 0.5 V to 1.3 V with the increase of width of black phosphorene nanoribbon. We discuss the width dependent electronic transport through the transmission spectra, density of states and transmission eigenstates. The varied coupling between molecule and electrodes accounts for changed current. It is concluded that the width of black phosphorene nanoribbon influences the electronic transport, and the increased width of black phosphorene nanoribbon reduces the rectifying ratio in black phosphorene based lateral Schottky heterojunction.

The effect of the undoped GaN/buffer-layer interface on the operation of Schottky diodes and MESFET devices

The effect of the interfacial region lying in between undoped GaN (u-GaN) and the buffer-layer on the forward current properties of lateral-type GaN Schottky diodes and planner GaN metal-semiconductor-field-effect-transistors (MESFETs) grown on sapphire substrates has been investigated. Experimental results have revealed higher current densities for devices grown on patterned sapphire substrates (PSS) compared to flat sapphire substrates (FSS) owing to the different carrier transport properties of the interfacial regions. Simulations using the charge transport model showed a good agreement with the experimental results. It is disclosed that the interfacial region is acting as channel in which the current passes in between the device metallic contacts. Owing to the presence of the interfacial regions, the lateral Schottky diodes exhibit high current densities but without change in their on-state-voltage, whereas the planar MESFETs could hardly reach cut-off or show saturation behavior. Studying the effect of the interfacial region on the operation of GaN power devices would help in optimizing the device design and efficiency, and further facilitate their monolithic integration with GaN-based LEDs.

Tunable Ohmic, p-Type Quasi-Ohmic, and n-Type Schottky Contacts of Monolayer SnSe with Metals

Monolayer (ML) SnSe, a p-type IV–VI semiconductor, has drawn tremendous attention because of its chemical stability, high electrostatic gating efficiency, and carrier mobility, and it has been synthesized in different ways. We have comprehensively investigated the properties of the interfaces between ML SnSe and some regular metals by using first-principles calculations. Metallization of ML SnSe appears in ML SnSe–Ag, −Al, −Au, −Cu, and −Cr systems. Lateral n-type Schottky contacts with electron Schottky barrier heights of 0.42 and 0.32 eV are formed, respectively, when ML SnSe contacts with metals Ag and Al. Also, a lateral p-type quasi-ohmic contact with a hole Schottky barrier height of 0.02 eV is formed when ML SnSe contacts with metal Au. Surprisingly, ohmic contacts are formed when ML SnSe contacts with metals Cr and Cu. Our research not only has a deep understanding of the characteristics of the interfaces between ML SnSe and the metals but also offers a reference in the electrode selection for ML SnSe devices.

Asymmetric Double‐Gate β‐Ga2O3 Nanomembrane Field‐Effect Transistor for Energy‐Efficient Power Devices

AbstractThe ultra‐wide bandgap and cost‐effective melt‐growth of β‐Ga2O3 ensure its advantages over other wide bandgap materials, and competitive electrical performance has been demonstrated in various device structures. In this paper, an asymmetric double‐gate (ADG) β‐Ga2O3 nanomembrane field‐effect transistor (FET) comprised of a bottom‐gate (BG) metal‐oxide field‐effect transistor and a top‐gate (TG) metal‐semiconductor field‐effect transistor (MESFET) is demonstrated. Schottky contact properties are validated by characterizing the lateral Schottky barrier diode (SBD), which exhibits high rectification ratio and low ideality factor. The top‐gate β‐Ga2O3 MESFET shows reasonable electrical performance with a high breakdown voltage, as anticipated by three terminal off‐state breakdown measurement. These properties are further enhanced by double‐gate operation, and superior device performance is demonstrated; positive‐shifted threshold voltage and reduced subthreshold slope enable the asymmetric double‐gate β‐Ga2O3 FET to operate at low power, and almost twice as much transconductance is demonstrated for high‐frequency operation. These results show the great potential of asymmetric double‐gate β‐Ga2O3 FETs for energy‐efficient high‐voltage and ‐frequency devices with optimal material and structure co‐designs.

High-performance lateral GaN Schottky barrier diode on silicon substrate with low turn-on voltage of 0.31 V, high breakdown voltage of 2.65 kV and high-power figure-of-merit of 2.65 GW cm−2

We demonstrate high-performance AlGaN/GaN lateral Schottky barrier diodes (SBDs) with Mo anode and low turn-on voltage of 0.31 V. AlGaN/GaN SBDs with anode to cathode spacing of 6/10/15/20/25 μm achieve a breakdown voltage (BV) of 0.83/1.23/1.62/2.46/2.65 kV, yielding a power figure-of-merit (FOM) of 1.53/1.82/1.77/2.65/2.12 GW cm−2. The power FOM of 2.65 GW cm−2 and BV of 2.65 kV are the best results of AlGaN/GaN SBDs on silicon substrate. Combined with the good dynamic performance with only 10% Ron increase when switched from a −600 V stress for 10 ms, GaN SBDs verify their great promise for future power electronic applications.