Schottky Drain Research Articles

A 2.8 kV Breakdown Voltage α-Ga2O3 MOSFET with Hybrid Schottky Drain Contact.

Among various polymorphic phases of gallium oxide (Ga2O3), α-phase Ga2O3 has clear advantages such as its heteroepitaxial growth as well as wide bandgap, which is promising for use in power devices. In this work, we demonstrate α-Ga2O3 MOSFETs with hybrid Schottky drain (HSD) contact, comprising both Ohmic and Schottky electrode regions. In comparison with conventional Ohmic drain (OD) contact, a lower on-resistance (Ron) of 2.1 kΩ mm is achieved for variable channel lengths. Physics-based TCAD simulation is performed to validate the turn-on characteristics of the Schottky electrode region and the improved Ron. Electric-field analysis in the off-state is conducted for both the OD and HSD devices. Furthermore, a record breakdown voltage (BV) of 2.8 kV is achieved, which is superior to the 1.7 kV of the compared OD device. Our results show that the proposed HSD contact with a further optimized design can be a promising drain electrode scheme for α-Ga2O3 power MOSFETs.

Impact of heavy ions on a-Si:H/PolySi bilayer thin film transistors with Schottky barrier source and drain based on Nickel Silicide

This study investigates the influence of heavy ion irradiation on thin film transistors (TFTs) based on an a-Si:H/PolySi active layer and Schottky barrier-based source and drain. Through the use of Technology Computer-Aided Design (TCAD) simulations, we analyze the impact on device performance. We examine the ambipolar device characteristics by varying the thickness of the active layer (Poly-Si) and studying the corresponding physics. Our results reveal that reducing the active layer thickness from 140 to 80 nm decreases the magnitude of the threshold voltage (|VT|) for both nMOS and pMOS operating voltages. Additionally, the subthreshold slope is reduced for both nMOS and pMOS as the active layer thickness is decreased from 140 to 80 nm.Further, we investigated the transient response of the drain current to heavy ion irradiation in the sensitive regions across the Schottky barrier-based source and drain. We specifically analyze the phenomenon of bipolar amplification for various Linear Energy Transfer (LET) values, ranging from 0.1 MeV cm2/mg to 100 MeV cm2/mg. Our findings indicate that increasing the LET values from 0.1 MeV cm2/mg to 100 MeV cm2/mg results in amplified bipolar behavior and a drain current overshoot of over 10 % for both pMOS and nMOS operating voltages. To summarize, this work highlights the effects of heavy ion irradiation on TFTs with an a-Si:H/PolySi active layer and Schottky barrier-based source and drain. The study explores the influence of active layer thickness on device characteristics and demonstrates the transient response of drain current under different LET values. These findings contribute to a better understanding of the behavior and performance of TFTs subjected to heavy ion irradiation.

Gaps in the Y-Function Method for Contact Resistance Extraction in 2D Few-Layer Transition Metal Dichalcogenide Back-Gated FETs

Y-Function method is often used for 2D TMD back-gated FETs, attributed to its simplicity and the lithographic challenges in processing transfer length method (TLM) test structures over 2D TMD flakes. While the contact resistance extracted from the Y-Function method was shown to be comparable to the TLM method in an early work, its applicability was never tested rigorously for the entire experimental range of 2D TMD FETs. This work presents the limitations and failure conditions of the Y-Function method when used for extracting contact resistance in back-gated, few-layer TMD FETs. We have found that the Y-Function method does not apply to the entire experimental range, such as ohmic/Schottky barrier, source-drain electric field, contact resistance, etc., particularly for the layered material-based FETs. The influence of the Schottky barrier and drain bias is investigated thoroughly for four different 2D materials (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , MoSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The experimental findings are then used to narrow down extraction window/conditions for the Y-Function method, which gives contact resistance estimation closer to TLM based approach for few-layer, back-gated TMD FETs.

Leakage mitigation in NW FET using negative Schottky junction drain and its process variation analysis

In this work, a Schottky junction on the drain side employing low workfunction (WF) metal is proposed as a method to suppress the OFF-state leakage in nanowire (NW) field-effect transistor (FET). Instead of a highly n+ doped drain, low WF metal with negative electron Schottky barrier height (SBH) as a drain minimizes the lateral band-to-band tunneling (L-BTBT) considerably. L-BTBT is the movement of carriers (holes) from the drain conduction band into the channel valence band during the OFF-state. Impact of varying WF at channel–drain junction on the device characteristics is studied. It is observed that SBH \(\leqslant 0\) eV is required to mitigate L-BTBT compared to the conventionally doped and junctionless (JL) NW counterpart. Furthermore, unlike L-BTBT, leakage in NW Schottky drain (SD) comprises of holes tunneling through the SB from the metal drain into the channel and is termed as the lateral SB tunneling (L-SBT). In contrast with JL NW FET, the process variation immunity (varying channel doping, \({N}_{\mathrm{Ch}}\) and NW diameter, \({d}_{\mathrm{NW}}\)) and the ON-state current of the proposed device are not compromised at the expense of lower OFF-state L-SBT. Instead, the device is less susceptible to process variations and retains the ON-state performance of the NW MOSFET. For a ± 20% change in \({N}_{\mathrm{Ch}}\), \(\Delta {I}_{\mathrm{OFF}}\)/\({I}_{\mathrm{OFF}}\) of 7% compared to 97% in NW JL FET is observed.

Experimental Demonstration of Monolithic Bidirectional Switch With Anti-Paralleled Reverse Blocking p-GaN HEMTs

A monolithic bidirectional switch based on anti-paralleled two reverse blocking p-GaN HEMTs has been proposed and demonstrated in this work. The recessed Schottky drain technique is utilized to effectively reduce the on-state voltage and thus lowering the power loss of bidirectional switches. A significant reduction in parasitic elements and switch area is obtained by monolithic integration. The fabricated bidirectional switch exhibits a threshold voltage of ~1.85 V, on-state voltage of ~0.63 V, and the forward and reverse off-state breakdown voltages of ~650 V at I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S1-S2</sub> = 1 μA/mm. In addition, the function of proposed bidirectional switch as an AC power chopper has been successfully verified.

High-performance reverse blocking p-GaN HEMTs with recessed Schottky and p-GaN isolation blocks drain

In this Letter, the p-GaN high electron mobility transistor (HEMT) with hybrid drain of recessed Schottky (RS) and p-GaN isolation blocks' drain (HSP drain) is proposed and fabricated for good reverse blocking capability. The related operation mechanism has been investigated and revealed. The proposed device features a drain terminal consisting of the array-distributed recessed Schottky and p-GaN isolation blocks. Based on the features, the reverse leakage current (5 × 10−9 A/mm at VDS = −100 V) is obviously reduced by two orders of magnitude compared with that (5 × 10−7 A/mm) of p-GaN HEMTs only with recessed Schottky (RS) drain, which is the lowest leakage current among the reported GaN-on-Si reverse blocking transistors. The introduction of these p-GaN isolation blocks has a negligible impact on Von (Von = 0.63 V). Therefore, a good improvement in the trade-off between the reverse leakage current and Von could be achieved because of the significant reduction in the reverse leakage current without sacrificing Von. In addition, the reverse breakdown voltage of −800 V at 1 μA/mm with a substrate grounded in the proposed device is evidently improved compared with the counterpart (−680 V), which is attributed to effective alleviation of the high electric field near the HSP drain. These results demonstrate the significance and potential of p-GaN HEMTs with HSP drain in reverse blocking applications.

Quasi-vertical GaN-on-Si reverse blocking power MOSFETs

We demonstrate quasi-vertical reverse blocking (RB) MOSFETs on 6.7 μm thick GaN grown on a 6 inch Si substrate by metalorganic chemical vapor deposition. The RB capability was achieved by replacing the ohmic drain with a quasi-vertical Schottky drain, resulting in a RB voltage of ∼300 V while preserving the ON-resistance (R on,sp). Schottky contacts on etched i-GaN surface were realized through an optimized fabrication process based on tetramethylammonium hydroxide treatments. The fabricated RB-MOSFET had a low R on,sp of 4.75 mΩ cm2, current density of ∼0.9 kA cm−2 and a forward blocking voltage of 570 V.

Room Temperature Hydrogen Sensing Investigation of Zinc Oxide Schottky Thin-Film Transistors: Dependence on Film Thickness

Radio frequency (RF) sputtered ZnO thin-film transistors (ZnO TFTs) with titanium/palladium (Ti/Pd) Schottky source and drain electrodes grown on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /n-Si substrate have been investigated with a compatible fabrication process for different channel thicknesses ranging from 50 to 200 nm as room temperature (RT) hydrogen sensors. Rapid and concentration-dependent (500-4500 ppm) sensor responses (in terms of drain current increase due to the lowering of the Schottky barrier height) with the maximum sensitivity of 72.7% have been achieved excluding the need of heating with relatively fast response/recovery times under RT. Apart from selectivity analysis of the sensors toward methane, acetone, and nitric oxide, structural, optical, mechanical, and electrical characteristics of the devices depending on film thickness are studied. The performance of the sensors in terms of repeatability, time-dependent stability, and under humid ambient conditions has been demonstrated. Hydrogen adsorption kinetics has also been investigated from a thermodynamic analysis.

More Than 3000 V Reverse Blocking Schottky-Drain AlGaN-Channel HEMTs With &gt;230 MW/cm2 Power Figure-of-Merit

In this letter, more than 3000 V reverse blocking Schottky-drain AlGaN-channel HEMTs are demonstrated for the first time. By using Schottky drain technology, forward breakdown voltage $\text{V}_{\textsf {FB}}$ (at 10 $\mu \text{A}$ /mm) is improved from 1850~2100 V to 2200~2600 V for ${L} _{\textsf {GD}}=\textsf {22}\mu \text{m}$ . Due to the high breakdown electric field of AlGaN material, reverse blocking voltage ${V} _{\textsf {RB}}$ (at 10 $\mu \text{A}$ /mm) reaches as high as −1950 ~ −2200 V. For HEMTs with ${L} _{\textsf {GD}}=\textsf {52}\mu \text{m}$ , record high ${V} _{\textsf {FB}}$ of >3000 V and ${V} _{\textsf {RB}}$ of >3000 V have been achieved. The leakage current is as low as 6.06 nA/mm at ${V} _{\textsf {DS}}=-\textsf {2000}$ V.

Optimization of Source/Drain Schottky Barrier Height for be SOI Mosfet

New devices architectures have been proposed to enable the evolution of semiconductors technology. One possibility is the reconfigurable transistors [1], i.e., transistor that can act as an n-type or as a p-type, which could enable circuits performing more than one function [2]. A new reconfigurable planar device was proposed/fabricated at Laboratorio de Sistemas Integraveis (LSI) from University of Sao Paulo (USP) using SOI substrate [3]. The named BE (Back Enhanced) SOI MOSFET (Patent BR 102015020974-6, 2015) is a kind of undopped junctionless SOI transistor and it shows the benefit of a simpler fabrication process compared to non-planar similar devices. In order to enable the good operation of the BE SOI for both types of transistors, the source/drain Schottky contact electrode perform an essential role. This work investigates the influence of the source/drain electrode metal workfunction on the drain current levels of the n-type and p-type BE SOI MOSFET in order to optimize its behavior. Figure 1 shows a schematic profile of the device. The work principle of the BE SOI MOSFET is based on different back bias (VGB) in each case. For a positive enough VGB, an electron channel is formed at the back interface that connects the source, channel and drain. In this case it is working like the n-type BE SOI MOSFET. This current path can be interrupted by the front gate (VGF). The electrostatic coupling due to VGB and VGF can deplete the channel, thus ceasing the drain current. Analogously, for a negative enough VGB, a hole channel is formed at the back interface and the p-type BE SOI MOSFET is obtained. The drain current characteristics of this transistor were explored in previous work [4]. Schottky source and drain contacts are required in this device. When the current flows, the charges tunnel through the Schottky barriers as indicated in figure 2. Consequently, the Schottky Barrier Height (SBH) influences at the current level. Higher SBH reduces the amount of tunneling charges. Figures 3 and 4 shows the simulated drain current in the BE SOI MOSFET as a function of VGF for metal workfunctions (ΦM) varying between 4.1V and 5.1V. The simulations performed in numerical Synopsys Sentaurus TCAD [5] considered only the dependence of the SBH on the metal workfunction and were calibrated using experimental data. The |VGB| value used is 25V and the drain to source voltage |VDS| is 100mV. The SBH for electrons directly increases with ΦM, therefore the simulated drain current in the n-type BE SOI (figure 3) decreases as ΦM rises. For lower values of ΦM (near conduction band level of the silicon), it was observed higher currents. In these situations the SBH is small, thus most of the electron current is by thermionic emission over the barrier and the contact exhibit an ohmic behavior. An analogous phenomenon is observed in the p-type device. The SBH for holes directly decreases with ΦM, hence the simulated drain current in the p-type BE SOI (figure 4) increases as ΦM reduces. In the same manner, the hole current for higher values of ΦM (near valence band level) is mostly by thermionic emission. In order to evaluate similar current levels for the n-type and p-type transistors, an optimal ΦM value must be selected. Figure 5 shows the comparison of the simulations of both types of transistors for an overdrive voltage VGT=VGF-VT=1V, where VT is the threshold voltage. It is possible to observe that the ratio of the maximum current levels is compatible with the charge mobility difference between electrons and holes. The inset graph shows the details of the region where the current of the n-type and p-type transistors intersect (at ΦM=4.57V). This workfunction value corresponds the BE SOI MOSFET with similar current levels for both types. The parameter that most affects the current level in the n-type and p-type BE SOI MOSFET is the metal workfunction of the drain and source Schottky contacts. Other optimizations can be performed to aim higher currents such the use of UTBB SOI substrate or alternative materials in order to enhance the performance of this device. This work evaluated the difference of the current levels in both types of transistors. Simulations results showed that ΦM=4.57V enables similar SBH, and therefore, similar electron and hole current levels. The simplicity of fabrication and the reconfigurability aspect makes the BE SOI MOSFET an interesting candidate for future applications. Figure 1

900 V Reverse-Blocking GaN-on-Si MOSHEMTs With a Hybrid Tri-Anode Schottky Drain

In this letter, we present high-performance GaN-on-Si metal-oxide-semiconductor high electron mobility transistors with record reverse-blocking (RB) capability. By replacing the conventional ohmic drain with a hybrid tri-anode Schottky drain, a high reverse breakdown voltage ( ${V}_{\text {B}}^{\text {R}}$ ) of −900 V was achieved (at $1~\mu \text{A}$ /mm with grounded substrate), along with a small reverse leakage current ( ${I}_{\text {R}}$ ) of ~20 nA/mm at −750 V. The devices also presented a small turn- on voltage ( ${V}_{{ \mathrm{\scriptscriptstyle ON}}}$ ) of 0.58 ± 0.02 V, a small increase in forward voltage ( $\Delta {V}_{\text {F}}$ ) of ~0.8 V, a high ON/OFF ratio over 1010, and a high forward breakdown voltage ( ${V}_{{{\text {B}}}}^{{{\text {F}}}}$ ) of 800 V at 20 nA/mm with grounded substrate. These results demonstrate a new milestone for RB GaN transistors, and open enormous opportunities for integrated GaN power devices.

Schottky bipolar I-MOS: An I-MOS with Schottky electrodes and an open-base BJT configuration for reduced operating voltage

In this paper, we have proposed a novel impact ionization MOS (I-MOS) structure, called the Schottky bipolar I-MOS, with Schottky source and drain electrodes and utilizing the open-base bipolar junction transistor (BJT) configuration for achieving reduction in the operating voltage of the I-MOS transistor. We report, using 2-D simulations, a low operating voltage (∼1.1 V) and a low subthreshold swing (∼3.6 mV/Decade). For the corresponding p-i-n I-MOS, the operating voltage is ∼5.5 V. The operating voltage of the Schottky bipolar I-MOS is the lowest reported operating voltage for silicon based I-MOS transistors. The nearly 80% reduction in the operating voltage of the Schottky bipolar I-MOS makes it suitable for applications requiring low operating voltages. The Schottky bipolar I-MOS is also expected to have an improved reliability over the p-i-n I-MOS since high energy carriers, induced by impact ionization near the drain, do not have to pass under the gate region in the channel. The use of Schottky contacts instead of heavily doped source and drain regions and the low channel doping level reduces the required thermal budget for device fabrication. The low operating voltage, low subthreshold swing and possibly improved reliability of the Schottky bipolar I-MOS, makes it a potential solution for applications where steep subthreshold slope transistors are being explored as alternative to the conventional MOS transistor.

Effect of high-temperature annealing for single-Ni-layer gate in AlGaN/GaN high-electron-mobility transistors

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Schottky gate contacts are strong candidates for high-power applications with high-frequency operation. The existence of interfacial traps between Schottky gate contacts and an AlGaN surface is one of the issues causing relatively high gate leakage current in these HEMTs. High-temperature gate annealing, which reduces the density of traps owing to the interfacial reaction between Schottky gate contacts and an AlGaN surface, was investigated using a single-Ni-layer gate structure to prevent the alloying of conventional stacked metal layers such as Ni/Au and Pt/Au. As a result, a strong gate annealing temperature dependence of Schottky characteristics was observed and this dependence also caused drain current collapse. In addition, it was confirmed that 700 °C is the optimal gate annealing temperature for improving both the Schottky characteristics and drain current collapse. These results are attributed to the change in the density of interfacial trap states.

Reverse blocking characteristics and mechanisms in Schottky-drain AlGaN/GaN HEMT with a drain field plate and floating field plates**Project supported by the National Natural Science Foundation of China (Grant Nos. 61204085, 61334002, 61306017, 61474091, 61574112, and 61574110).

In this paper, a novel AlGaN/GaN HEMT with a Schottky drain and a compound field plate (SD-CFP HEMT) is presented for the purpose of better reverse blocking capability. The compound field plate (CFP) consists of a drain field plate (DFP) and several floating field plates (FFPs). The physical mechanisms of the CFP to improve the reverse breakdown voltage and to modulate the distributions of channel electric field and potential are investigated by two-dimensional numerical simulations with Silvaco-ATLAS. Compared with the HEMT with a Schottky drain (SD HEMT) and the HEMT with a Schottky drain and a DFP (SD-FP HEMT), the superiorities of SD-CFP HEMT lie in the continuous improvement of the reverse breakdown voltage by increasing the number of FFPs and in the same fabrication procedure as the SD-FP HEMT. Two useful optimization laws for the SD-CFP HEMTs are found and extracted from simulation results. The relationship between the number of the FFPs and the reverse breakdown voltage as well as the FP efficiency in SD-CFP HEMTs are discussed. The results in this paper demonstrate a great potential of CFP for enhancing the reverse blocking ability in AlGaN/GaN HEMT and may be of great value and significance in the design and actual manufacture of SD-CFP HEMTs.

Temperature-dependent electrical characterization of high-voltage AlGaN/GaN-on-Si HEMTs with Schottky and ohmic drain contacts

In this work we present results of electrical parameters characterization of high-voltage AlGaN/GaN high electron mobility transistors with ohmic and Schottky drain electrodes on silicon substrates. The use of Schottky-drain contacts improves breakdown voltage (VBR), which was VBR=900V for LGD=20μm in contrast to VBR=505V for ohmic-drain contacts. Both types of transistors exhibit drain current density of 500mA/mm and leakage current of 10μA/mm. Temperature-dependent characterization reveals a drain current density decrease with increasing temperature. The Schottky-drain HEMTs are characterized by lower increase of the Ron (ΔRon=250% at 200°C) in comparison to ohmic drain contacts (ΔRon=340% at 200°C) relative to the room temperature due to decrease of on-set voltage of Schottky-drain HEMTs.

Study of the leakage current suppression for hybrid-Schottky/ohmic drain AlGaN/GaN HEMT

The leakage current suppression mechanism in AlGaN/GaN High Electron Mobility Transistors (HEMTs) is investigated. It is known that leakage current can cause severe reliability problems for HEMT devices and conventional AlGaN/GaN HEMT devices suffer from detrimental off-state drain leakage current issues, especially under high off-state drain bias. Therefore, a leakage current suppression technique featuring hybrid-Schottky/ohmic-drain contact is discussed. Through the 2-zones leakage current suppression mechanism by the hybrid-Schottky/drain metal including the shielding effect of the rough ohmic-drain metal morphology and the drain side electric field modulation, AlGaN/GaN HEMT featuring this novel technique can significantly enhance the leakage current suppression capability and improve the breakdown voltage. An analytical method using loop-voltage-scanning is proposed to illustrate the optimization procedure of the hybrid-Schottky/ohmic drain metallization on leakage current suppression. Through the comparison of the loop leakage current hysteresis of conventional ohmic drain HEMT and hybrid-Schottky/ohmic drain, the leakage current suppression mechanism is verified through the leakage current considering surface acceptor-like trap charging/discharging model. Device featuring the hybrid-Schottky/ohmic drain technique shows an improvement in breakdown voltage from 450V (with no Schottky drain metal) to 855V with a total drift region length of 9μm, indicating enhanced off-state reliability characteristics for the AlGaN/GaN HEMT devices.

Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain

In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages (BVs) simultaneously in AlGaN/GaN high-electron mobility transistors (HEMTs). The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from 72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmicdrain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from −5 V to −49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.

P-doping-free III-nitride high electron mobility light-emitting diodes and transistors

We report that a simple metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet emission at 3.4 eV at a small forward bias larger than ∼2 V at room temperature. Based on the surface states distribution of AlGaN, a mature impact-ionization-induced Fermi-level de-pinning model is proposed to explain the underlying mechanism of the electroluminescence (EL) process. By experimenting with different Schottky metals, Ni/Au and Pt/Au, we demonstrated that this EL phenomenon is a “universal” property of metal-AlGaN/GaN Schottky diodes. Since this light-emitting Schottky diode shares the same active structure and fabrication processes as the AlGaN/GaN high electron mobility transistors, straight-forward and seamless integration of photonic and electronic functional devices has been demonstrated on doping-free III-nitride heterostructures. Using a semitransparent Schottky drain electrode, an AlGaN/GaN high electron mobility light-emitting transistor is demonstrated.

Reverse blocking enhancement of drain field plate in Schottky-drain AlGaN/GaN high-electron mobility transistors

In this paper, we present the combination of drain field plate (FP) and Schottky drain to improve the reverse blocking capability, and investigate the reverse blocking enhancement of drain FP in Schottky-drain AlGaN/GaN high-electron mobility transistors (HEMTs). Drain FP and gate FP were employed in a two-dimensional simulation to improve the reverse blocking voltage (VRB) and the forward blocking voltage (VFB). The drain-FP length, the gate-FP length and the passivation layer thickness were optimized. VRB and VFB were improved from −67 V and 134 V to −653 V and 868 V respectively after optimization. Simulation results suggest that the combination of drain FP and Schottky drain can enhance the reverse blocking capability significantly.

Unidirectional AlGaN/GaN-on-Si HFETs with reverse blocking drain

We have developed a novel unidirectional AlGaN/GaN-on-Si heterojunction field-effect transistor (HFET) with reverse blocking drain. A recessed Schottky contact was incorporated into a conventional ohmic drain electrode to prevent the undesired reverse current flow while reducing the turn-on voltage in forward current characteristics. The combination of recessed Schottky and ohmic electrodes significantly reduced the turn-on voltage in comparison with a conventional Schottky drain. A turn-on voltage of 0.4 V, an off-state forward breakdown voltage of 615 V, and a reverse blocking drain voltage of −685 V were achieved for the gate-to-drain distance of 12 µm.