Vertical Schottky Barrier Diodes Research Articles

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.

Epilayer thickness effect on the electrical and breakdown characteristics of vertical β-Ga2O3 Schottky barrier diode

The current–voltage and breakdown characteristics of Au/Ni/β-Ga2O3 Schottky barrier diodes were investigated as a function of β-Ga2O3 epilayer thickness in the range of 6–19 μm. The X-ray rocking curves indicated that the full-width half-maximum is reduced with increasing epilayer thickness, implying an improvement in the crystallinity of β-Ga2O3 epilayer. The barrier heights of the field-plated β-Ga2O3 Schottky barrier diode with epitaxial layer thickness of 6, 12, and 19 μm were obtained as 1.01, 1.03, and 1.04 eV, with the ideality factor values being 1.21, 1.19, and 1.46, respectively. The higher ideality factors could be associated with the existence of inhomogeneity at the metal–semiconductor interface. The series resistance of the Schottky diode obtained increased with increasing epilayer thickness. The Schottky diode fabricated on 19 μm thick epitaxial layer exhibited a higher breakdown voltage of 490 V. The increase in epilayer thickness led to the widening of depletion region, resulting in lower electric field over a larger distance. This could be a main cause of the enhancement of the breakdown voltage characteristics of β-Ga2O3 Schottky barrier diode.

Fully vertical AlN-on-SiC Schottky barrier diodes

We demonstrated fully vertical Schottky barrier diodes (SBDs) that have a Si-doped AlN drift layer directly grown on an n-type 4H-SiC substrate by metal-organic CVD. The AlN SBD with a Ni anode showed a clear rectifying characteristic at 300–500 K and a rectification ratio of about 10–2. We found that the leakage current of the vertical AlN-on-SiC devices is affected by defects in the AlN drift layer and Schottky interface.

Estimation of Electron Drift Mobility along the <i>c</i>-Axis in 4H-SiC by Using Vertical Schottky Barrier Diodes

Electron mobility along the c-axis is the most important in SiC because the current flows along this direction in vertical SiC devices. However, previous reports on the drift mobility along the c-axis are still limited because of the difficulty of sample preparation or analysis. In this study, the authors presented the method to estimate the electron drift mobility of a lightly-doped epitaxial layer by using SiC(0001) vertical Schottky barrier diodes (SBDs). For the analyses, the effects of current spreading and series resistance were carefully considered based on experimental results obtained from SBDs with various device parameters, leading to a more accurate estimation. The mobility along the c-axis was obtained as 1070 ± 290 cm2/Vs for a donor density of 1 × 1015 cm-3, and it was compared with the results by Hall effect measurement.

High-k Dielectrics-Based Electric Field Engineering in β-Ga2O3 Power Diodes

We present β-Ga2O3 high-voltage Schottky barrier diodes (SBD) incorporating advanced electric field engineering approaches through the use of high-permittivity dielectrics. We present two approaches: 1) the lateral dielectric superjunction SBD, where the electric field within the drift layer is modified from triangular to rectangular profile, enhancing the breakdown voltage and enabling the use of higher drift layer doping to reduce on-resistance, and 2) the vertical high-k RESURF trench SBD, which leverages the reduced surface electric field effect (RESURF) to reduce the electric field at the metal-semiconductor junction and reverse leakage currents.A superjunction-like structure uses charge balance to push the VBR-Ron-sp trade-off beyond the material’s unipolar figure of merit. The lack of p-type doping in β-Ga2O3 makes the realization of such structures very difficult. However, field flattening can be achieved in β-Ga2O3 drift layers using a high permittivity material with appropriate choice of dielectric constant, device aspect ratio and semiconductor/dielectric width. An analytical model is discussed to highlight the device design strategy and experimental demonstration is reported in the lateral geometry. 500 nm of Si-doped Ga2O3 epitaxial layer with a sheet charge of 1.6×1013 cm-2 is grown using metal organic vapor phase epitaxy (MOVPE). Trenches with three different fin widths (WFin = 2, 5, 10 µm) were made and high-k dielectric BaTiO3 (BTO) with dielectric constant of 220 is deposited on the sample. A low specific on resistance of 1.65 mΩ-cm2 is observed for LAC = 5µm due to the high charge density epitaxial lateral Fins. For the SBD with LAC = 5µm and WFin = 5µm, a high average electric field of ~3 MV/cm (VBR/ LAC) is estimated across the entire length of the device. A very high Baliga's figure of merit (BFOM) of 1.35 GW/cm2 is observed for the RESURF SBD with LAC=5µm and WFin=2µm (VBR=1.49 kV and Ron-sp=1.65 mΩ-cm2), surpassing SiC unipolar FOM when considering just the conducting area.While superjunction-like structures effectively flatten the electric field inside the drift layer, high electric fields at the metal/semiconductor junction results in increased leakage current at large reverse bias, particularly in the case of vertical Schottky Barrier Diodes (SBDs). To circumvent this challenge, we present the approach of β-Ga2O3 Vertical Trench Schottky Barrier Diode (SBD) with a high-permittivity dielectric RESURF. The incorporation of a trench geometry, coupled with the high-permittivity dielectric RESURF, effectively reduces the surface electric field at the metal-semiconductor junction. This reduction facilitates the use of a lower work-function anode contact, further diminishing the turn-on voltage. The use of high-k dielectric also significantly reduces the dielectric leakage contribution to the overall reverse leakage of the diode. Large-area SBDs with areas of 1mm2 and 4mm2 exhibit pulsed forward current of 6A/20A and a catastrophic breakdown voltage of 1.74kV/1.4kV, surpassing other β-Ga2O3-based large-area power diodes, while small-area SBDs (200×200 µm2) do not exhibit catastrophic breakdown until 3kV. The large-area SBDs also demonstrate lower capacitance, stored charge, and stored energy compared to commercial SiC SBDs, indicating potential for superior switching performance. The combination of lower stored charge and a low forward voltage drop results in an excellent trade-off between conduction and switching power loss, yielding a QCVF figure of merit comparable to commercial bare die SiC SBDs. We demonstrate the potential of high permittivity dielectrics-based extreme field engineering to push the performance limits of β-Ga2O3 diodes for next-generation power electronics.We acknowledge funding from AFOSR MURI program (Dr. Ali Sayir) and Coherent/II-VI foundation.

Displacement damage effect of proton irradiation on vertical β-Ga2O3 and SiC Schottky barrier diodes (SBDs)

In this study, we fabricated vertical Schottky barrier diodes (SBDs) based on wide bandgap semiconductor beta-phase gallium oxide (β-Ga2O3) and silicon carbide (SiC), respectively, and conducted proton irradiation experiments to analyze the radiation hardness of the SBDs comparatively. The effects of proton radiation on the performance of SBDs were assessed through measurements of forward current, capacitance, and breakdown characteristics. Both devices exhibited degradation in current and capacitance characteristics following proton irradiation, attributed to displacement damage (DD). Notably, the β-Ga2O3-based SBD demonstrated more pronounced deterioration compared to the SiC-based device despite similar vacancy distributions as confirmed by SRIM simulation. Moreover, a decrease in contact radius correlated with exacerbated degradation in the current characteristics of the β-Ga2O3-based SBD. Following proton irradiation, breakdown voltages of both devices increased due to elevated resistance induced by displacement damage. While both β-Ga2O3 and SiC-based SBDs experienced displacement damage under high fluence proton irradiation, the extent of performance degradation varied depending on the dimensions and quality of epitaxial and substrate layers.

A 1.6 kV Ga2O3 Schottky Barrier Diode with a Low Reverse Current of 1.2 × 10-5 A/cm2 Enabled by Field Plates and N Ion-Implantation Edge Termination.

In this work, by employing field plate (FP) and N ion-implantation edge termination (NIET) structure, the electrical performance of the β-Ga2O3 Schottky barrier diode (SBD) was greatly improved. Ten samples of vertical SBDs were fabricated to investigate the influence of the relative positions of field plates (FPs) and ion implantation on the device performance. The device with the FP of 15 μm and the ion implantation at the edge of the Schottky electrode exhibited a breakdown voltage (Vbr) of 1616 V, a specific on-resistance (Ron,sp) of 5.11 mΩ·cm2, a power figure of merit (PFOM) of 0.511 GW/cm2, and a reverse current density of 1.2 × 10-5 A/cm2 @ -1000 V. Compared to the control device, although the Ron,sp increased by 1 mΩ·cm2, the Vbr of the device increased by 183% and the PFOM increased by 546.8%. Moreover, the reverse leakage current of the device with the FP and NIET structure decreased by three orders of magnitude. The TCAD simulation revealed that the peak electric field at the interface decreased from 7 MV/cm @ -500 V to 4.18 MV/cm @ -1000 V. These results demonstrate the great potential for the β-Ga2O3 SBD with a FP and NIET structure in power electronic applications.

Design Strategy of Vertical GaN Power Schottky Barrier Diodes with p‐GaN Junction Termination Extension and Experimental Demonstration of Selective p‐Doping by Implantation

Herein, the impact of the key structural parameters on the breakdown characteristics of the vertical gallium nitride (GaN) power Schottky barrier diodes (SBDs) with p‐GaN junction termination extension (JTE) structures by numerical simulation is systematically investigated. With a p‐type GaN structure incorporated at the edge of the Schottky junction, the electric field crowding at the edge of Schottky anode can be alleviated, effectively avoiding the premature breakdown of the devices. It is found that the acceptor concentration, thickness, width, and surface charge density of the incorporated JTE are closely associated with the electric field distribution and the reverse breakdown characteristics. The vertical SBDs with optimum p‐GaN JTE parameters feature a dramatic improvement in Baliga's figure of merit, without obvious degradation in the forward and dynamic performance. Selective p‐doping and acceptor activation is also demonstrated, which verifies the fabrication feasibility of the proposed JTE structures. Through the results, the way can be paved for the design and fabrication of high‐performance GaN vertical power devices toward high‐voltage, high‐power, and high‐speed applications.

Carrier density control of Sb-doped rutile-type SnO2 thin films and fabrication of a vertical Schottky barrier diode

We report on the control of carrier density in r-SnO2 thin films grown on isostructural r-TiO2 substrates by doping with Sb aiming for power-electronics applications. The carrier density was tuned within a range of 3 × 1016–2 × 1019 cm−3. Two types of donors with different activation energies, attributed to Sb at Sn sites and oxygen vacancies, are present in the thin films. Both activation energies decrease as the concentration of Sb increases. A vertical Schottky barrier diode employing a Sb:r-SnO2/Nb:r-TiO2 exhibits a clear rectifying property with a rectification ratio of 103 at ±1 V.

Improvement of Ga2O3 vertical Schottky barrier diode by constructing NiO/Ga2O3 heterojunction

The high critical electric field strength of Ga2O3 enables higher operating voltages and reduced switching losses in power electronic devices. Suitable Schottky metals and epitaxial films are essential for further enhancing device performance. In this work, the fabrication of vertical Ga2O3 barrier diodes with three different barrier metals was carried out on an n–-Ga2O3 homogeneous epitaxial film deposited on an n+-β-Ga2O3 substrate by metal−organic chemical vapor deposition, excluding the use of edge terminals. The ideal factor, barrier height, specific on-resistance, and breakdown voltage characteristics of all devices were investigated at room temperature. In addition, the vertical Ga2O3 barrier diodes achieve a higher breakdown voltage and exhibit a reverse leakage as low as 4.82 ×10−8 A/cm2 by constructing a NiO/Ga2O3 heterojunction. Therefore, Ga2O3 power detailed investigations into Schottky barrier metal and NiO/Ga2O3 heterojunction of Ga2O3 homogeneous epitaxial films are of great research potential in high-efficiency, high-power, and high-reliability applications.

Demonstration of vertical schottky barrier diodes based on α-Ga2O3 thin films enabled by corundum structured rh-ITO bottom electrodes

Demonstration of vertical schottky barrier diodes based on α-Ga2O3 thin films enabled by corundum structured rh-ITO bottom electrodes

β-Ga2O3 Schottky Barrier Diode with Ion Beam Sputter-Deposited Semi-Insulating Layer

Vertical Schottky barrier diodes based on an ion beam sputter (IBS)-deposited β-Ga2O3 film on a single-crystalline (2¯01) unintentionally doped (UID) β-Ga2O3 with a Ni contact were developed. To form ohmic Ti/Ni contacts, the IBS-Ga2O3/UID β-Ga2O3 structures were wet-etched, and an indium tin oxide (ITO) intermediate semiconductor layer (ISL) was deposited on the opposite surface of the UID β-Ga2O3. The IBS-deposited Ga2O3 layer was polycrystalline and semi-insulating. Low leakage currents, rectification ratios of 3.9 × 108 arb. un. and 3.4 × 106 arb. un., ideality factors of 1.43 and 1.24, Schottky barrier heights of 1.80 eV and 1.67 eV as well as breakdown voltages of 134 V and 180 V were achieved for diodes without and with ITO-ISL, respectively. The surface area of the IBS-Ga2O3 film acted as a thin dielectric layer and, together with the preliminary wet etching, provided low leakage currents and relatively high Schottky barrier heights. Diodes with a Schottky barrier based on a Ni/IBS-deposited Ga2O3 film contact were demonstrated for the first time.

A simulation study of vertical Ga2O3 Schottky barrier diodes using field plate termination

The precision design of beta-phase gallium oxide (β-Ga2O3) power devices requires appropriate physical properties, including a breakdown electric field intensity. To clarify the breakdown electric field in β-Ga2O3, we fabricated vertical Schottky barrier diodes (SBDs) with a field plate (FP) on a β-Ga2O3 (001) epitaxial layer and simulated their breakdown situations under reverse bias. The calculated breakdown voltages of the SBD with a single FP were consistent with the experimental values when assuming an electric field criterion of 5 MV cm−1 in β-Ga2O3. By designing a SBD with a double FP according to the electric field criterion above, a breakdown voltage over 2 kV and specific on-resistance of 6.9 mΩ cm2 were realized simultaneously. This results in an electric field criterion that is useful for the design parameter of β-Ga2O3 devices to balance a high breakdown voltage and low on-resistance.

Over 6 μm thick MOCVD-grown low-background carrier density (1015 cm−3) high-mobility (010) β-Ga2O3 drift layers

This work reports high carrier mobilities and growth rates simultaneously in low unintentionally doped (UID) (1015 cm−3) metalorganic chemical vapor deposition (MOCVD)-grown thick β-Ga2O3 epitaxial drift layers, with thicknesses reaching up to 6.3 μm, using triethylgallium (TEGa) as a precursor. Record-high room temperature Hall mobilities of 187–190 cm2/V s were measured for background carrier density values of 2.4–3.5 × 1015 cm−3 grown at a rate of 2.2 μm/h. A controlled background carrier density scaling from 3.3 × 1016 to 2.4 × 1015 cm−3 is demonstrated, without the use of intentional dopant gases such as silane, by controlling the growth rate and O2/TEGa ratio. Films show smooth surface morphologies of 0.8–3.8 nm RMS roughness for film thicknesses of 1.24–6.3 μm. Vertical Ni Schottky barrier diodes (SBDs) fabricated on UID MOCVD material were compared with those fabricated on hydride vapor phase epitaxy material, revealing superior material and device characteristics. MOCVD SBDs on a 6.3 μm thick epitaxial layer show a uniform charge vs depth profile of ∼ 2.4 × 1015 cm−3, an estimated μdrift of 132 cm2/V s, breakdown voltage (VBR) close to 1.2 kV, and a surface parallel plane field of 2.05 MV/cm without any electric field management—setting record-high parameters for any MOCVD-grown β-Ga2O3 vertical diode to date.

Ultra-low reverse leakage in large area kilo-volt class β-Ga2O3 trench Schottky barrier diode with high-k dielectric RESURF

We introduce vertical Schottky barrier diodes (SBDs) based on β-Ga2O3 with trench architecture, featuring a high-permittivity dielectric RESURF structure. These diodes are designed for application demanding high voltage and current capacities while maintaining ultra-low reverse leakage currents. The trench design plays a pivotal role in reducing the electric field at the metal–semiconductor junction, thereby yielding minimal reverse leakage attributed to field emission under high reverse bias conditions. Additionally, the incorporation of a high-k dielectric helps to suppress leakage through the trench bottom corner dielectric layer. The small area trench SBD (200 × 200 μm2) demonstrates a breakdown voltage exceeding 3 kV, accompanied by a reverse leakage current of less than 1 μA/cm2 at 3 kV. Moving on to larger area devices, the 1 × 1 and 2 × 2 mm2 devices exhibit breakdown voltages of 1.8 and 1.4 kV, while accommodating pulsed forward currents of 3.5 and 15 A, respectively. The capacitance, stored charge, and switching energy of the trench SBDs are also found to be less than the similarly rated commercial SiC SBDs, reinforcing their potential for enhanced switching efficiency.

Effect of gamma irradiation on β -Ga2O3 vertical Schottky barrier diode

In this paper, the radiation effect of gamma irradiation (60Co) on the Au/Ni/β-Ga2O3 vertical Schottky barrier diodes (SBDs) was investigated for total doses of about 1 Mrad (Si). The SBDs were characterized by current density–voltage (J–V) and capacitance–voltage (C–V) measurements. Compared with original β-Ga2O3 SBDs, it was found that Schottky barrier height Φb increases from 1.08 to 1.12 eV, the ideality factor n decreases from 1.07 to 1.02, and the specific on-resistance Ron,sp decreases from 3.34 to 2.95 mΩ·cm2 for the irradiated β-Ga2O3 SBDs. In addition, the carrier concentration calculated from the C–V measurements increases slightly after gamma irradiation. The temperature-dependent current–voltage characteristics and conductance-frequency measurements indicate that the Schottky contact interface of β-Ga2O3 SBDs had been slightly improved after irradiation. These results suggest that β-Ga2O3 SBDs have high intrinsic gamma irradiation hardness.

Electrical Properties of Ga2O3 Schottky Barrier Diodes with and without Mesa Structure

Devices based on wide bandgap (WBG) semiconductors like silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) are ideal for high-power electronics in harsh environments. Among the WBG semiconductors, ultrawide bandgap (UWBG) β-phase gallium oxide (Ga2O3), EG ≈ 4.8 eV, is emerging as a replacement for the current commercially available wide bandgap (WBG) power electronics due to its generational improvements in performance and manufacturing cost [1]. Ga2O3 has a high theoretical breakdown electrical field of 8 MV/cm which in turn gives its Baliga’s figure of merit for power devices that is larger than other WBG materials. The availability of high-quality Ga2O3 substrates produced from melt-grown bulk single crystals also facilitates the development of vertical power devices.In the current stage, the vertical Schottky barrier diode (SBD) with Ga2O3 can have an improved current spreading effect when compared to power diode devices from Si, SiC, and GaN. Especially, the Ga2O3 is expected to surpass the trade-off relationship between breakdown voltage (BV) and on resistance (Ron,sp) that other materials have [2]. Nevertheless, the Ga2O3 vertical SBD still cannot achieve the theoretical breakdown electric field. One of the key topics for WBG semiconductors application is a structure for improved electrical management such as field rings, junction termination extension, and field plates to reduce the leakage current in the reverse bias state.Here, we investigate the characteristics of Ga2O3 SBDs with and without mesa structure in extreme environments at high and low temperature. Conventional and mesa Ga2O3 SBDs were fabricated on the halide vapor phase epitaxy (HVPE) grown β-Ga2O3 (001). A Sn-doped substrate with 61016 cm-3 was used for the HVPE growth. In the SBD with mesa structure, the circular mesa with a diameter of 162 μm and a depth of 500 nm was formed around anode electrodes. The Ti/Au metal stack on the back side of the substrate acted as a cathode and the anode electrode deposited Ni/Au/Pt layers. After the fabrication process, current-voltage (I-V) measurements were performed on the SBDs between -5 V and 1 V. From the results, the values of Ron,sp at 0.7 V are 46.4 Ω•cm2 and 46.2 Ω•cm2 in conventional and mesa SBDs, respectively. And additionally, the leakage current at -5 V is reduced by approximately 44.3% in the mesa structure. To obtain the Schottky barrier height (SBH) from I-V and capacitance-voltage (C-V) measurements, the C-V was observed in the range of -5 V to 0.5 V at 100 kHz. The SBH values from I-V and C-V measurements, the mesa SBDs have 1% - 5% larger SBH compared to the conventional structure, and it could be related to lower leakage current. Moreover, the depletion depths of conventional and mesa SBDs were 52.2 nm and 57.8 nm, respectively, from C-V measurements. For considering the electrical characteristics in extreme temperatures, the I-V measurements of both SBDs structure will be measured between 75 K to 525 K. From an initial low temperature measurement series, we determine a Richardson constant of 49 A/cm2 comparable to what has been reported by other groups. Furthermore, we will extend the study by performing deep-level transient spectroscopy (DLTS) to understand the defect information in Ga2O3.

High breakdown electric field diamond Schottky barrier diode with HfO2 field plate

In this work, we fabricated a vertical diamond Schottky barrier diode (SBD) with a high breakdown electric field of 4.8 MV/cm and a forward current density of 2361 A/cm2. Compared with a regular diamond SBD, the breakdown electric field of SBD with a HfO2 field plate (FP) increased from 183 to 302 V, the current swing (ION/IOFF) was on the order of 1011. As the thickness of the HfO2 FP increased from 200 to 400 nm, the breakdown voltage of the SBD increased from 280 to 314 V, and the corresponding breakdown electric field increased from 4.5 to 5 MV/cm. We also measured the current–voltage characteristics at different temperatures to investigate the cause of the high on-resistance. As the measured temperature increased from 25 to 150 °C, the on-resistance of the device decreased from 4.7 to 1.7 mΩ·cm2. By studying the interface between HfO2 and the diamond, we found that HfO2 can reduce the interface state density of the Schottky contact. The interface state density of Zr/HfO2/diamond was lower than 1.5 × 1013 eV−1·cm−2. This work provides a simple strategy for realizing high-performance diamond SBDs.

β-Ga2O3 junction barrier Schottky diode with NiO p-well floating field rings

Recently, β-Ga2O3, an ultra-wide bandgap semiconductor, has shown great potential to be used in power devices blessed with its unique material properties. For instance, the measured average critical field of the vertical Schottky barrier diode (SBD) based on β-Ga2O3 has reached 5.45 MV/cm, and no device in any material has measured a greater before. However, the high electric field of the β-Ga2O3 SBD makes it challenging to manage the electric field distribution and leakage current. Here, we show β-Ga2O3 junction barrier Schottky diode with NiO p-well floating field rings (FFRs). For the central anode, we filled a circular trench array with NiO to reduce the surface field under the Schottky contact between them to reduce the leakage current of the device. For the anode edge, experimental results have demonstrated that the produced NiO/β-Ga2O3 heterojunction FFRs enable the spreading of the depletion region, thereby mitigating the crowding effect of electric fields at the anode edge. Additionally, simulation results indicated that the p-NiO field plate structure designed at the edges of the rings and central anode can further reduce the electric field. This work verified the feasibility of the heterojunction FFRs in β-Ga2O3 devices based on the experimental findings and provided ideas for managing the electric field of β-Ga2O3 SBD.

Simulation study of vertical diamond Schottky barrier diode with field plate assisted junction termination extension

In this paper, we designed vertical diamond Schottky barrier diodes with a field plate assisted junction termination extension (FP-JTE) structure by using Silvaco TCAD. It demonstrates that the JTE structure is more effective to suppress the electric field crowding around the electrode edges than the FP, but it also increases the on-resistance due to the decreasing conduction area. Then, the FP-JTE diamond SBDs are designed to realize the trade-off between the breakdown voltage and on-resistance. It is found that the JTE length should be shorter than the FP to enhance the current conduction, but it needs to cover the cathode edge to suppress the electric field crowding. We also confirm that the FP-JTE SBDs with the JTE length increase from the sidewall toward the center are recommended to take advantage of both FP and JTE structures.