Junction Barrier Schottky Research Articles

6.5 kV SiC PiN and JBS Diodes’ Comparison in Hybrid and Full SiC Switch Topologies

This work investigates the performance of state-of-the-art non-commercial 6.5 kV Silicon Carbide (SiC) PiN and Junction Barrier Schottky (JBS) diodes in hybrid (Si IGBT with SiC diode) and full SiC (SiC MOSFET with SiC diode) switch topologies. The static and dynamic performance has been systematically evaluated at distinct temperatures, gate resistances and currents for each configuration. The SiC PiN diode presented higher current density capability and lower leakage current density than the JBS diode. Moreover, in most cases, the SiC PiN diode-based topologies demonstrated slightly higher total switching losses compared to the SiC JBS diode-based equivalent configurations. A loadability analysis in a three-level NPC converter is presented to evaluate the potential of each configuration in a converter application. The SiC PiN technology presented a 25% power extension compared to the SiC JBS technology with similar efficiency at typical industrial drives switching frequency operation when comparing same-active-area diode technologies. Finally, a long-term reliability test (H3TRB) is presented to demonstrate the SiC PiN diode technology’s potential for operation in harsh environments. Such characteristics show the advantage of the 6.5 kV SiC PiN diode when a high current density (>100 A/cm2), high efficiency and reliability are required.

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.

Study of leakage current degradation based on stacking faults expansion in irradiated SiC junction barrier Schottky diodes

Abstract A comprehensive investigation was conducted to explore the degradation mechanism of leakage current in SiC junction barrier Schottky (JBS) diodes under heavy ion irradiation. We propose and verify that the generation of stacking faults (SFs) induced by the recombination of massive electron--hole pairs during irradiation is the cause of reverse leakage current degradation based on experiments results. The irradiation experiment was carried out based on Ta ions with high linear energy transfer (LET) of 90.5 MeV/(mg/cm2). It is observed that the leakage current of the diode undergoes the permanent increase during irradiation when biased at 20% of the rated reverse voltage. Micro-PL spectroscopy and PL micro-imaging were utilized to detect the presence of SFs in the irradiated SiC JBS diodes. We combined the degraded performance of irradiated samples with SFs introduced by heavy ion irradiation. Finally, three-dimensional (3D) TCAD simulation was employed to evaluate the excessive electron–hole pairs (EHPs) concentration excited by heavy ion irradiation. It was observed that the excessive hole concentration under irradiation exceeded significantly the threshold hole concentration necessary for the expansion of SFs in the substrate. The proposed mechanism suggests that the process and material characteristics of the silicon carbide should be considered in order to reinforcing against the single event effect of SiC power devices.

Design and evaluation of β-Ga2O3 junction barrier schottky diode with p-GaN heterojunction

A novel design for a junction barrier Schottky (JBS) diode based on a p-GaN/n-Ga2O3 heterojunction is proposed, exhibiting superior static characteristics and a higher breakdown capability compared to the traditional Ga2O3 Schottky barrier diode (SBD). By utilizing wide-bandgap p-type GaN, the β-Ga2O3 JBS diodes demonstrate a turn-on voltage (V on ) of approximately 0.8 V. Moreover, a breakdown voltage (V br ) of 880 V and a specific on-resistance (R on,sp ) of 3.96 mΩ·cm2 are achieved, resulting in a Baliga’s figure of merit (BFOM) of approximately 0.2 GW /cm 2. A forward current density of 465 A cm−2 at a forward voltage of 3 V is attained. The simulated reverse leakage current density remains low at 9.0 mA cm−2 at 800 V. Floating field rings, in conjunction with junction termination extension (JTE), were utilized as edge termination methods to attain a high breakdown voltage. The impact of β-Ga2O3 periodic fin width fluctuations on the electrical characteristics of JBS was investigated. Due to the enhanced sidewall depletion effect caused by p-type GaN, the forward current (I F ) and reverse current (I R ) decrease when the β-Ga2O3 periodic fin width decreases. The findings of this study indicate the remarkable promise of p-GaN/n-Ga2O3 JBS diodes for power device applications.

Field management in NiO x /β-Ga2O3 merged-PIN Schottky diodes: simulation studies and experimental validation

In recent years, p-type NiO x has emerged as a promising alternative to realize kilovolt-class β-Ga2O3-based PN junction diodes. However, only a handful of studies could realize β–Ga2O3-based unipolar diodes using NiO x as a guard ring or floating rings. In this work, we investigate the device design of NiO x /β-Ga2O3 unipolar diodes using the technology computer aided design simulations and experimental validations. We show that a systematic electric field management approach can potentially lead to NiO x /β-Ga2O3 heterojunction unipolar diode and offer enhanced breakdown characteristics without a severe compromise in the ON-state resistance. Accordingly, the NiO x /β-Ga2O3 heterojunction diode in the merged-PIN Schottky configuration is shown to outperform the regular Schottky diode or junction barrier Schottky diode counterpart. The analysis performed in this work is believed to be valuable in the device design of β-Ga2O3-based unipolar diodes that use a different p-type semiconductor candidate as guard rings and floating rings.

Design optimization of wide-gate swing E-mode GaN HEMTs with junction barrier Schottky gate

To increase the gate swing, a GaN-based high-electron-mobility transistor with a junction barrier Schottky gate (JBS-HEMT) was proposed. Compared to conventional p-GaN Schottky gate HEMTs (Conv-HEMT), the high electric field at the surface is transferred to the pn junction inside the body, and the extended depletion region of the pn junction shields the surface Schottky contact interface for the JBS-HEMT. After fitting the model to the reported device, the proposed JBS-HEMT was simulated and optimized using the Sentaurus TCAD tool. The simulation results of the optimized JBS-HEMT demonstrate a high gate breakdown voltage (17.6 V), which is 158.5% higher than the gate breakdown voltage of the Conv-HEMT (11.1 V) and a lower gate leakage current of six orders of magnitude than the Conv-HEMT at the gate-to-source voltage of 10 V. The proposed JBS-HEMT exhibits a positive threshold voltage (1.68 V) and excellent threshold voltage stability, and the maximum threshold voltage drift of the JBS-HEMT (+0.237 V) is smaller than that of the Conv-HEMT (−0.714 V) under gate stress conditions. The peak transconductance of the JBS-HEMT (186 mS mm−1) at athe drain-to-source voltage of 10 V showed almost no reduction compared to the Conv-HEMT (189 mS mm−1), which solves the problem of decreased transconductance capability of the reported GaN HEMT with a p-n junction gate (PNJ-HEMT). It was confirmed that the JBS-HEMT has excellent gate stability and potential for power electronics applications.

Unveiling microstructural damage for leakage current degradation in SiC Schottky diode after heavy ions irradiation under 200 V

Single-event burnout and single-event leakage current (SELC) in silicon carbide (SiC) power devices induced by heavy ions severely limit their space application, and the underlying mechanism is still unclear. One fundamental problem is lack of high-resolution characterization of radiation damage in the irradiated SiC power devices, which is a crucial indicator of the related mechanism. In this Letter, high-resolution transmission electron microscopy (TEM) was used to characterize the radiation damage in the 1437.6 MeV 181Ta-irradiated SiC junction barrier Schottky diode under 200 V. The amorphous radiation damage with about 52 nm in diameter and 121 nm in length at the Schottky metal (Ti)–semiconductor (SiC) interface was observed. More importantly, in the damage site the atomic mixing of Ti, Si, and C was identified by electron energy loss spectroscopy and high-angle annular dark-field scanning TEM. It indicates that the melting of the Ti–SiC interface induced by localized Joule's heating is responsible for the amorphization and the possible formation of titanium silicide, titanium carbide, or ternary phases. The mushroom-like hillock in the Ti layer can be attributed to Rayleigh–Taylor instability, as another evidence for ever-happened localized melting near the Schottky interface. These modifications at nanoscale in turn cause localized degradation of the Schottky contact, resulting in permanent increase in leakage current. This experimental study provides very valuable clues for a thorough understanding of the SELC mechanism in SiC diodes.

Novel design and modelling of SiC junction barrier Schottky diode with improved Baliga FOM under high-temperature applications

A novel 650 V/50 A 4H–SiC junction barrier Schottky diode (JBSD) featuring a stripe-square composite cell design (SSC-JBSD) is proposed in this paper to improve the high-temperature performance. A model of the resistance of the JBS (RJBS) is established to explain the mechanism. The particular cell design of the SSC-JBSD forms a circular current distribution, which can improve the forward current and suppress the degeneration of RJBS caused by the lower electron mobility at high temperatures. The combination of the stripe and square P+ regions achieves a high current and a lower power loss under high temperature while maintaining a high breakdown voltage. Specifically, the power loss of the SSC-JBSD with a forward current of 50 A only increases by 6.9 % under 450 K compared to that under 300 K, while that of the conventional JBS diode (Conv-JBSD) increases by 14.1 %. And the Baliga figure of merit (FOM) of the SSC-JBSD is 15.6 % higher than that of the Conv-JBSD under a temperature of 450 K. The on-state self-heating measurement shows that the temperature of the SSC-JBSD is approximately 30 K lower than that of the Conv-JBSD after 5 s of constant on-state operation with a forward current of 50 A. The proposed SSC-JBSD demonstrates superior performance at high temperatures, making it an available replacement for Conv-JBSD in harsh environments characterized by high temperatures and large currents.

Defects evolution in n-type 4H-SiC induced by electron irradiation and annealing

Radiation damage produced in 4H-SiC by electrons of different doses is presented by using multiple characterization techniques. Raman spectra results indicate that SiC crystal structures are essentially impervious to 10 MeV electron irradiation with doses up to 3000 kGy. However, irradiation indeed leads to the generation of various defects, which are evaluated through photoluminescence (PL) and deep level transient spectroscopy (DLTS). The PL spectra feature a prominent broad band centered at 500 nm, accompanied by several smaller peaks ranging from 660 to 808 nm. The intensity of each PL peak demonstrates a linear correlation with the irradiation dose, indicating a proportional increase in defect concentration during irradiation. The DLTS spectra reveal several thermally unstable and stable defects that exhibit similarities at low irradiation doses. Notably, after irradiating at the higher dose of 1000 kGy, a new stable defect labeled as R 2 (Ec − 0.51 eV) appeared after annealing at 800 K. Furthermore, the impact of irradiation-induced defects on SiC junction barrier Schottky diodes is discussed. It is observed that high-dose electron irradiation converts SiC n-epilayers to semi-insulating layers. However, subjecting the samples to a temperature of only 800 K results in a significant reduction in resistance due to the annealing out of unstable defects.

Ga2O3/NiO junction barrier Schottky diodes with ultra-low barrier TiN contact

Power Schottky barrier diodes (SBDs) face an inherent trade-off between forward conduction loss and reverse blocking capability. This limitation becomes more severe for ultra-wide bandgap (UWBG) SBDs due to the large junction field. A high Schottky barrier is usually required to suppress the reverse leakage current at the price of an increased forward voltage drop (VF). This work demonstrates a Ga2O3 junction barrier Schottky (JBS) diode that employs the embedded p-type NiO grids to move the peak electric field away from the Schottky junction, thereby allowing for the use of an ultra-low barrier TiN Schottky contact. This JBS diode concurrently realizes a low VF of 0.91 V (at forward current of 100 A/cm2) and a high breakdown voltage over 1 kV, with the VF being the lowest in all the reported vertical UWBG power diodes. Based on the device characteristics measured up to 200 °C, we further analyze the power loss of this JBS diode across a wide range of operational duty cycles and temperatures, which is found to outperform the TiN/Ga2O3 SBDs or NiO/Ga2O3 PN diodes. These findings underscore the potential of low-barrier UWBG JBS diodes for high-frequency, high-temperature power electronics applications.

Comparison of Electrical Conductivity and Schottky Behavior of 4‐[2‐(9‐anthryl)vinyl]pyridine Based Two 1D Coordination Polymers of Zn(II) and Cd(II)

AbstractWith the increase in demand of electronic devices in the modern civilization, research in material science is being projected to grow in faster rate. In this facet, coordination polymer (CP) based electronic device is one of the promising candidates to the material researchers. Herein, two new Zn(II) and Cd(II) based one‐dimensional (1D) CPs, denoted as [Zn(4‐avp)2(5‐nip)] ⋅ (solvent)x (1) and [Cd(4‐avp)(5‐nip)(CH3OH)] (2) have been synthesized using relatively less explored highly conjugated polycyclic aromatic hydrocarbon (PAH) based monodentate ligand, 4‐[2‐(9‐anthryl)vinyl]pyridine (4‐avp) and bidentate linker 5‐nitroisophthalic acid (H25‐nip). In this instance, the CP 1 creates 1D chain polymer, while CP 2 is made up with 1D ladder polymer. It is interesting to note that both the CPs exhibit semiconducting nature and generate metal‐semiconductor (MS) junction Schottky barrier diodes (SBDs). However, Cd‐based CP 2 shows higher charge transport as compared to Zn‐CP 1, which could be due to stronger π⋅⋅⋅π contacts as well as larger size of Cd metal in CP 2. The experimental results are well corroborated with theoretical density of states (DOS) calculations.

Low turn-on voltage and 2.3 kV β -Ga2O3 heterojunction barrier Schottky diodes with Mo anode

In this work, we propose combining a low work function anode metal and junction barrier Schottky structure to simultaneously achieve low turn-on voltage (Von) and high breakdown voltage (BV), which alleviates the dilemma that high BV requires high Schottky barrier height (SBH) and high Von. Molybdenum (Mo) is used to serve as the anode metal to reduce the SBH and facilitate fast turn-on to achieve a low Von. To resolve the low SBH related low BV issue, a p-NiO/n-Ga2O3-based heterojunction structure is used to enhance β-Ga2O3 sidewall depletion during the reverse state to improve the BV. With such a design, a low Von = 0.64 V(@1A/cm2) and a high BV = 2.34 kV as well as a specific on-resistance (Ron,sp) of 5.3 mΩ cm2 are demonstrated on a 10 μm-drift layer with a doping concentration of 1.5 × 1016 cm−3. β-Ga2O3 JBS diodes with low Von = 0.64 V and a power figure of merit of 1.03 GW/cm2 show great potential for future high-voltage and high-efficiency power electronics.

Failure analysis of heavy ion-irradiated silicon carbide junction barrier Schottky diodes

An analysis of damage, including single event burnout (SEB) and single event leakage current (SELC) caused by heavy ion irradiation in silicon carbide (SiC) junction barrier Schottky diodes (JBSDs), was performed using Auger electron spectroscopy (AES), emission microscope (EMMI), focused ion beam (FIB), transmission electron microscopy (TEM) and other methods. The damage of SEB extending from the Schottky contact through the epitaxial layer to the SiC substrate was observed. The damage causing SELC was related to the micro-burnout of the Schottky contact. It was concluded that the damage of Schottky contact was induced by incident high-energy particles under a large electric field, forming a leakage current path, resulting in SEB and SELC in the SiC device.

Two‐Dimensional Characterization of Au/Ni/Thin Heavily‐Mg‐Doped p‐/n‐GaN Structure under Applied Voltage by Scanning Internal Photoemission Microscopy

The two‐dimensional characterization of the Au/Ni/thin p+‐GaN/n−‐GaN structure, which is a part of a junction barrier Schottky structure, is demonstrated by scanning internal photoemission microscopy (SIPM) method. In the SIPM photoyield image using a blue laser, small photocurrents based on the internal photoemission effect by electron injection across the metal/semiconductor interface (from Ni to GaN) are detected in the center of the electrode. On the periphery, large photocurrents in the opposite direction are detected. These currents are caused by the hole injection from Ni into p+‐GaN layer and the electrical field in the laterally extended depletion layer at the edge. By using a violet laser, large photocurrents based on the fundamental absorption generated in the depletion layer of the n−‐GaN layer are uniformly detected over the electrode. It is conformed that SIPM can be available for quasi‐three‐dimensional characterization of this structure.

Demonstration of High Avalanche Capability in 1200 V-Rated SiC Junction Barrier Schottky Diodes With Record Avalanche Energy Density

Demonstration of High Avalanche Capability in 1200 V-Rated SiC Junction Barrier Schottky Diodes With Record Avalanche Energy Density

Acceleration of solving drift-diffusion equations enabled by estimation of initial value at nonequilibrium

<abstract><p>In this study, a novel method enabled by estimation of initial value guess at nonequilibrium was proposed to accelerate drift-diffusion equations in semiconductor device simulation. The initial value guess was obtained by solving analytical model about electrical potential with the decoupling algorithm. By obtaining the initial value directly at the target bias voltage, the proposed method eliminated time-consuming bias ramping process in the classical method starting from the equilibrium state, thereby accelerating the whole process. The method has been applied to a junction barrier Schottky (JBS) diode for validation. Numerical results showed that the proposed method achieves convergence within 10 iterations at several reverse bias voltages, achieving significant reduction of iteration number compared to the classical method using the bias ramping process. It demonstrated that the proposed method holds high feasibility to facilitate the semiconductor device property prediction in relatively regular device structure in the case of low current. With further improvements, this method can also be applied to more complex devices.</p></abstract>

Hybrid Schottky and heterojunction vertical β-Ga2O3 rectifiers

Schematic of hybrid Schottky and Junction Barrier Schottky Ga2O3 rectifiers. Breakdown voltage increased as the proportion of heterojunction area did, from 1.2 kV for Schottky rectifiers to 6.2 kV for pure heterojunction devices.

(Invited) Role of Heterojunctions in Metal Oxide Heterostructures for Energy and Environmental Applications

Heterostructures made from metal oxide semiconductors are fundamental for the development of high-performance gas sensors and electrocatalysts, for examples. Here, I will introduce hierarchical heterostructures composed of p-, n-type and insulating metal oxide shells.Precisely controlled films of alternating metal oxides can be uniformly deposited onto the inner and outer walls of the CNTs and onto mesoporous substrates by atomic layer deposition. The morphological, microstructural and electrical characteristics of the heterostructures were thoroughly investigated. Electrical resistance measurements highlighted the large influence of the metal oxides thickness and charge carriers types, suggesting that the conductivity of the electrodes are dominated by Schottky barrier junctions across the heterojunctions.The behavior of the heterostructured electrodes in sensors and in electrocatalysis applications was investigated for low concentrations of volatile organic compounds and pollutants, and the oxygen evolution reaction in acidic media, respectively. For examples, the gas sensing response of the heterostructures showed a strong dependence on the thickness of the metal oxide shell layers and the type of heterostructures formed. On the other hand, the electrocatalytic performances are strongly related to the surface catalyst/stabilization layer and the electrical conductivity of the heterostructured electrode.On the basis of the morphological, microstructural and electrical characterization, and electrode performances, the mechanisms which account for the performances of our heterostructured electrodes will be correlated and discussed.

(Invited) Towards GaN-on-GaN High-Power Electronic Devices

Application of gallium nitride (GaN) substrates in electronic and optoelectronic industries is constantly increasing. In order to fabricate wafers, GaN crystals of the highest structural quality and desired electrical (and sometimes optical) properties must be grown. Today, there are three main GaN crystallization methods: i/ halide vapor phase epitaxy (HVPE) with its derivatives: halide-free VPE and oxide VPE; ii/ sodium-flux; and iii/ ammonothermal. The last approach can be basic or acidic depending on what mineralizer is used to increase the solubility of GaN in the feedstock zone. In this paper we will focus on HVPE and basic ammonothermal growth of GaN [1]. Not only bulk growth will be presented. The HVPE method will also be discussed as the best method to crystallize the drift layers necessary for high-power vertical electronic devices (FET transistors, Schottky diodes).One of the best methods for introducing dopants into semiconductors is ion implantation. The introduced structural damage can be removed by a proper annealing process. The high-temperature treatment enables also electrical and/or optical activation of the implanted dopants. In the case of GaN, annealing at high temperature (~1300°C - 1400°C) seems difficult. This compound loses its thermodynamic stability slightly above 800°C at atmospheric pressure. At higher temperature the crystal will decompose. One of the solutions is to anneal GaN at high nitrogen (N2) pressure. Such technology is called ultra-high-pressure annealing (UHPA) [2]. In this paper, application of UHPA for GaN crystals and layers implanted by different ions (acceptors and donors) will be presented. The latest results of the implantation with magnesium (Mg), beryllium (Be), zinc (Zn), and calcium (Ca) ions into GaN in order to obtain p-type conductivity will be discussed [3,4]. Silicon (Si) implantation into GaN for n-type doping will also be analyzed. Structural, electrical and optical properties of implanted GaN after UHPA will be discussed in terms of application for GaN-based devices.A kV class, low ON-resistance, vertical GaN junction barrier Schottky (JBS) diode with selective-area p-regions formed via Mg implantation followed by high-temperature, ultra-high pressure post-implantation activation anneal without a capping layer was already demonstrated [5]. The forward characteristics of the JBS diode showed ideality factor (n) 1.03, turn-on voltage (VON) 0.75 V, current ON/OFF ratio (at ±3 V) ~1011, and specific differential ON-resistance (RON) 0.6 mΩ·cm2. The breakdown voltage of the JBS diode was 915 V.

Novel digital terahertz device for three-state logic gate and phase coding based on graphene and Schottky barrier junctions

Terahertz technology, III-V group semiconductor devices, and graphene have great potential for broad applications in 6 G wireless communications. A novel digital terahertz device with nickel/GaN and graphene/GaN Schottky barrier junctions was proposed in this study. The patterned metal electrodes of the device, together with the graphene layer, formed a terahertz metasurface. The mechanisms of modulating the fermi level of graphene and the conductivity of the device to manipulate the transmission coefficient and reflected phase of terahertz waves were investigated using numerical calculations. The electrical and optical simulation results theoretically demonstrated that the three-state logic gate operation for the transmission coefficient of terahertz wave at 1.458 THz and the 1-bit reflected phase coding manipulation in 1.51–1.55 THz were realized. In addition, the maximum radar cross section reduction for the reflected wave was approximately 11.14 dB, comparing the designed coding sequences with the metal plate. These functions are mainly implemented by applying an external bias voltage to the device. This study provides a new and feasible strategy for designing digital terahertz manipulation devices.