Junction Barrier Schottky Research Articles

1.2-kV 4H-SiC Merged PiN Schottky Diode With Improved Surge Current Capability

This paper presents the design and experimental analysis of 1200-V 4H-silicon carbide (SiC) merged PiN Schottky (MPS) diodes. Design considerations and device performances of the MPS diodes are compared with those of the junction barrier Schottky (JBS) diodes via numerical simulation and experiments. Due to the limited P+ width/ratio in JBS diodes, p-n junction is not turned on until very high current/voltage bias is applied. This increases the device voltage drop and energy dissipation in high current stress conditions. Thanks to the wide P+ region design and the ohmic contact on the P +regions, the p-n junction turn-on voltage in MPS diodes is substantially decreased, and the surge current capability is improved accordingly. Furthermore, the surge capability of two layouts of the MPS diodes are compared. Layout A with ~60% high P+ ratio can improve the surge current capability by 10% and 20% compared with layout B design (with ~50% P+ ratio) and pure JBS diode (with ~40% P+ ratio), respectively. The reliability of the MPS diodes is studied by repetitive pulse surge current tests. No obvious degradation appears after 5500 test cycles under a surge current stress 20 times the device nominal current rating.

Design and Characterization of Area-Efficient Trench Termination for 4H-SiC Devices

In this paper, the operation mechanism of trench termination is investigated through 2-D numeric simulation on Silvaco. It is found that in trench termination, the electric field is terminated by the accumulated holes at the outer trench sidewall. In order to ensure a high termination breakdown voltage, the trench is refilled with a combination of SiO2 and polyimide (PI). Through various 2-D numerical simulations, the impact of structural parameters on breakdown voltage has been discussed, namely, trench depth (TD), trench width (TW), and sidewall tilt angle. The 3-D simulations are also conducted to investigate the effect of round corner radius on the device breakdown voltage and electric field in the dielectrics. Based on these results, the trench termination is designed and then fabricated along with a p-i-n diode. The measurement results show that a $14~\mu \text{m}$ wide trench is sufficient to terminate a voltage of 1750V (>96% of the ideal planar breakdown). Comparing with conventional field limiting rings junction termination extension (FLR/JTE) technology, this trench termination can significantly reduce the termination length by a factor of 4. As a result, the area efficiency is largely improved from 62% to around 90% for a 2A device conducting at 1000 A/cm2. These results indicate that the SiC device price can be substantially lowered with such an area-efficient trench termination technology. Furthermore, the 168-h high-temperature reverse bias (HTRB) test under 1200 V and 175 °C shows the potential of this trench termination for long-term reliable operation. Finally, unclamped inductive switching (UIS) tests have been conducted on fabricated devices. Compared to commercial SiC junction barrier Schottky diodes with FLR, fabricated p-i-n diodes with trench termination show significant higher avalanche capability.

All Electrodeposited Nanowire Array Based Tandem Junction Photoelectrochemical Devices

Large-scale solar fuel production using semiconductor based photoelectrochemical (PEC) system requires inexpensive, efficient and stable devices that can provide photovoltages sufficient to overcome both the thermodynamic and overpotential losses of the redox reaction. Here we report all electrodeposited multi-junction PEC devices for solar fuel production using serially connected CdSe based and CdTe based Schottky barrier junctions with photovoltages exceeding 1.0 V. These PEC devices are synthesized inside nanoporous alumina membranes with each nanoscale solar conversion units physically and electronically isolated from each other, making the entire device fault tolerant. The alumina membranes also serve to protect the semiconductor from chemical and PEC corrosion.

Degradation in electrothermal characteristics of 4H-SiC junction barrier Schottky diodes under high temperature power cycling stress

The electrothermal characteristics and degradation mechanism of 4H-SiC JBS under high temperature power cycling (HTPC) stress were investigated based on thermal structure function, failure analysis and electrothermal simulation. Results show that, the HTPC stress at different temperature conditions (maximum junction temperature Tjmax = 150 °C and Tjmax = 200 °C) have different effects on the reverse breakdown voltage (Vbr), reverse leakage current and the on-resistance (Ron-sp). It was that the increased reverse leakage currents with HTPC stress are due to the Schottky barrier lowering at the beginning. However, as the heat concentration effect increased at the metal/4H-SiC interface, the contribution of tunneling to leakage current is the major components. So the heat flux path and thermal distribution are very crucial to the reliability of chip and package. It can be concluded that the degradations of die-attach, die surface and metal/SiC interface are the main reliability limiting factors of SiC JBS diodes under high temperature applications.

Constructing functionalized plasmonic gold/titanium dioxide nanosheets with small gold nanoparticles for efficient photocatalytic hydrogen evolution

Small plasmonic Au nanoparticles (NPs)-decorated with TiO2 nanosheets were fabricated to improve the photocatalytic performance. The Au/TiO2 nanosheets with Au NPs of different sizes ranging from ∼3 nm to 28 nm were prepared by using hydrothermally obtained TiO2 nanosheets as substrate via urea and light reduction method. During synthesis, the obtained Au NPs through urea reduction treatment in different calcination temperatures possessed smaller size (∼3–13 nm) than those of the light reduction method (∼28 nm). The introduced Au NPs were tightly loaded on the surface of TiO2 nanosheets through in situ growth reduction process of chloroauric acid. The emergence of smaller Au NPs promoted the photocatalytic performance over Au/TiO2 nanosheets. The as-prepared Au/TiO2 nanosheets with small Au NP sizes of ∼3–5 nm showed the highest photocatalytic rate of hydrogen production (∼230 µmol·h−1) under xenon lamp illumination, exceeding more than twice that of Au/TiO2 nanosheets with loading of larger Au NPs (∼28 nm). The favorable constituents and combination of Au/TiO2 nanosheets provided large surface adsorptive sites for reactant adsorption, introduced plasmonic effects and formed Schottky barrier junction via surface plasmon resonance. The Schottky barrier height was lower due to the presence of smaller Au NPs, thereby enhancing the charge separation through the Schottky transfer hub to neighboring TiO2 nanosheets. The synergistic effect between the plasmonic hot carrier-driven Au NPs and TiO2 nanosheets was discussed. The photocatalytic mechanism was also proposed for the fabrication of visible light-restricted photocatalysts with smaller Au NPs.

Influence of Trench Design on the Electrical Properties of 650V 4H-SiC JBS Diodes

This work presents a design study of customized p+ arrays having influence on the electrical properties of manufactured 4H-SiC Junction Barrier Schottky (JBS) diodes with designated electrical characteristics of 5 A forward and 650 V blocking capabilities. The effect of the Schottky area consuming p+ grid on the forward voltage drop, the leakage current and therefore the breakdown voltage was investigated. A recessed p+ implantation, realized through trench etching before implanting the bottom of the trenches, results in a more effective shielding of the electrical field at the Schottky interface and therefore reduces the leakage current. Customizing the p+ grid array in combination with the trench structure, various JBS diode variants with active areas of 1.69 mm2 were fabricated whereas forward voltage drops of 1.58 V @ 5 A with blocking capabilities up to 1 kV were achieved.

Radiation Effects on 1.7kV Class 4H-SiC Power Devices: Development of Compact Simulation Models

Compact simulation models of two key silicon carbide power components, the Junction Barrier Schottky diode and the power MOSFET, which are taking into account the effect of irradiation by highenergy electrons, were developed. Two 1.7 kV class devices: the 14 A JBS diode C3D10170H and the 5 A SiC power MOSFETs C2M1000170D produced by Wolfspeed were irradiated by 4.5 MeV electrons in the dose range up to 2000 kGy. Electrical characteristics were measured prior to and after irradiation. Radiation defects were studied by deep level transient spectroscopy and the effect of irradiation on device characteristics was established. SPICE models taking into account the irradiation fluence were proposed and calibrated using the parameters extracted from experiment. Simulated characteristics show a very good agreement with reality.

Mechanisms and Characteristics of Large-Area High-Current-Density 4H-SiC Trench Junction Barrier Schottky Diodes

Mechanisms and characteristics of optimized main junction for 4H-SiC trench junction barrier Schottky (TMJBS) diodes were investigated by theories and experiments. From these simulation and experimental values, we can conclude that TMJBS device has better reverse performance, such as the best reverse blocking capability and lowest reverse surface leakage current than the conventional JBS and TJBS device while maintaining good forward characteristics. Furthermore, The large area TMJBS Diodes with high current density show the better reverse characteristics than the small area one at an acceptable forward characteristics. The TMJBS structure can significantly reduce the influence of the Schottky interface and is more suitable for manufacturing high current density and large area devices.

Enhanced Charge Collection in SiC Power MOSFETs Demonstrated by Pulse-Laser Two-Photon Absorption SEE Experiments

A two-photon absorption technique is used to understand the mechanisms of single-event effects (SEEs) in silicon carbide power metal–oxide–field-effect transistors (MOSFETs) and power junction barrier Schottky diodes. The MOSFETs and diodes have similar structures enabling the identification of effects associated specifically with the parasitic bipolar structure that is present in the MOSFETs, but not the diodes. The collected charge in the diodes varies only with laser depth, whereas it varies with depth and lateral position in the MOSFETs. Optical simulations demonstrate that the variations in collected charge observed are from the semiconductor device structure and not from metal/passivation-induced reflection. The difference in the spatial dependence of collected charge between the MOSFET and diode is explained by bipolar amplification of the charge carriers in the MOSFETs. Technology computer-aided design (TCAD) device simulations extend this analysis to heavy-ion-induced charge collection. In addition, there is discussion comparing this analysis with experimental results from prior works that show enhanced charge collection resulting from heavy-ion irradiation.

Influence of barrier inhomogeneities on transport properties of Pt/MoS2 Schottky barrier junction

The electrical transport properties of the Pt/MoS2 Schottky barrier junction have been investigated to explore the effect of lateral barrier inhomogeneities at the interface. The junction with a relatively thin layer (5 nm) of MoS2 exhibits rectifying behavior and changes into Ohmic nature on increasing the thickness of MoS2. The current-voltage (I–V) measurements on the Schottky barrier junction were performed in the temperature range of 200–350 K. Our detailed analysis of the temperature dependent I–V data shows the presence of a bi-fold charge transport mechanism across the Pt/MoS2 interface. Dipolar fields, present due to inhomogeneities at the interface, modify charge transport in addition to the thermionic emission mechanism attributed conventionally for the Schottky junctions. The model, assuming a Gaussian distribution of barrier heights due to the presence of lateral inhomogeneities, has been used to analyze and explain the temperature dependent I–V data. The effect of lateral inhomogeneities on the electrical properties of the Pt/MoS2 Schottky junction has been studied in a quantitative manner.

Simulation of Electrothermal Characteristics of 1200V/75A 4H-SiC JBS

In this paper the electrothermal properties of the 4H-SiC JBS (Junction barrier Schottky) diode is investigated. FloTHERM and Silvaco TCAD are used for electrothermal simulation at the same time. Firstly, the effect of Rjc (junction-to-case thermal resistance) on junction temperature is investigated, the result shows that the junction temperature is more sensitive to the Rjc in the current heating mode because of some kind of positive feedback. Then, a current pulse is applied to the JBS, result shows that this kind of positive feedback is especially noticeable. Finally, the JBS will be compared with PIN under high current density pulsed operation, in order to analyze their thermal sensitivity to Rjc.

Low Defect Thick Homoepitaxial Layers Grown on 4H-SiC Wafers for 6500 V JBS Devices

70-um thick homoepitaxial layers with very low defect density were grown on 6-inch 4° off-axis wafers using hot-wall chemical vapor deposition (CVD). Process optimization resulted in reduction of the density of triangular defects from 1.01 cm-2 to 0.14 cm-2. The treatment of wafer (CMP or selection) was essential. The in-situ etch process was optimized prior to the epitaxial growth. Junction Barrier Schottky diodes fabricated on the epitaxial films presented a typical I–V characteristic and a block voltage of 6500 V.

Effects of proton radiation on field limiting ring edge terminations in 4H–SiC junction barrier Schottky diodes

In this study, the effects of high-energy proton radiation on the effectiveness of edge terminations using field limiting rings (FLRs) in 4H–SiC junction barrier Schottky (JBS) diodes were examined in detail. The devices were irradiated using 5-MeV protons at fluences ranging from 5× 1012 cm−2 to 5× 1014 cm−2. Further, the reverse breakdown performances of the investigated devices were measured both before and after irradiation. Proton irradiation initially decreased the breakdown voltage (BV); subsequently, the BV was increased as the proton fluence increased. At a fluence of 5× 1013 cm−2, the BV was reduced by approximately 18%, whereas it was reduced by approximately 5% at a higher proton fluence of 5× 1014 cm−2. The related degradation mechanism that was associated with this phenomenon was also investigated using the numerical simulations of the current-voltage ( I - V ) and capacitance-voltage ( C - V ) characteristics of the device. The main contribution to the radiation-induced changes in BV originates from the variations of charge distribution at the SiO2/4H–SiC interface and the reduction of the net carrier density in the drift region. Both the aforementioned variations affect the spread of the electric field in the FLR edge termination regions.

1.38kV Merged Pin Schottky Rectifier for High Power Device Applications

In this paper, we have proposed a modified version of junction barrier schottky diode (JBS) with fused trench structure to enhance electrical properties. The device has an increased current density, low forward voltage drop, high breakdown voltage and large schottky contact area as compared to previous merged pin-junction barrier schottky diode.4H-SiC is used as a substrate and device is purely simulation based. To carry out simulation work Silvaco TCAD(ATLAS) is used. The simulated device has current density of 110 A/cm2 with schottky region having height of 2.5 μm and at a forward voltage drop of 2.5 V. The proposed device has more number of schottky contacts than the previous devices and it reduces the forward voltage drop by 20% at current density of 140 A/cm2. The output capacitance of this device, common JBS and earlier merged pin schottky diode are almost same. Moreover, the forward and reverse features of device are studied at room temperature (25 °C) as well as at higher temperatures.

Heavy Ion Transport Modeling for Single-Event Burnout in SiC-Based Power Devices

SiC power devices have been found experimentally to burn out from heavy ion strikes with linear energy transfers as low as 2.0 MeV $\cdot $ cm2/mg. In this paper, to better understand the failure mechanisms, we study the single-event burnout (SEB) phenomenon using a unified physics model between heavy ion radiation transport and device response. High-fidelity radiation data, generated from a general purpose Monte Carlo N-particle transport code (MCNP6.2), were modeled using a double Gaussian function to take into account both the heavy ion and the delta ray contributions. SiC junction barrier Schottky (JBS) diodes underwent 3-D TCAD electrothermal simulations using the double Gaussian model. This model was compared against other heavy ion models to determine the behavior of the thermal response from a heavy ion strike. The results reveal that there is a more rapid thermal response from models using high-fidelity heavy ion radiation data than approximated models provided by TCAD simulators. Peak temperature results from high-voltage SiC JBS diodes, which agree with the experimental observation of SEBs in SiC power devices.

Research of Single-Event Burnout in 4H-SiC JBS Diode by Low Carrier Lifetime Control

This paper presents the 2-D numerical simulation results of single-event burnout (SEB) in 4H-SiC junction barrier Schottky (JBS) diode by low carrier lifetime control (LCLC) for the first time. We investigate the SEB performance based on an 1800-V JBS structure and find that the most sensitive ion’s strike position is the middle of junction spacing because of the punchthrough of the electric field at anode contact. Then, the SEB hardening mechanism of LCLC is studied in this paper that the double-sided peak electric field can be effectively improved which results in a significantly decrease of maximal temperature. For the incident particle with different linear energy transfer values, we find that the SEB threshold voltage can be substantially enhanced when the carrier lifetime ( $\tau $ ) is under a certain value. In addition, the basic characteristics with LCLC are discussed that the forward and reversed characteristics are hardly affected.

A Physics-Based Compact Model of SiC Junction Barrier Schottky Diode for Circuit Simulation

A physics-based compact model of silicon carbide (SiC) junction barrier Schottky diode for circuit simulation is developed in this paper. The semiconductor physics mechanism in SiC, such as temperature-dependent mobility and incomplete ionization, are considered. The detailed device parameters, including drift region concentration, drift thickness, active area, and Schottky barrier height, are modeled. Then, a datasheet-oriented parameter extraction procedure for the device parameters is presented for three kinds of commercial SiC Schottky diodes with junction barrier structure. The model is implemented in the circuit simulator PSpice. In order to verify this model, the Technology Computer-Aided Design Sentaurus simulation is conducted with the device parameters and physical models, which shows a good agreement with the PSpice simulation.

A 4H-SiC junction barrier Schottky diode with segregated floating trench and super junction

A 4H-SiC Junction Barrier Schottky Diode with Segregated Floating Trench and Super Junction (S-FT SJ JBS) is presented in this paper. By adopting segregated integrated trench and super junction, the high electric field not only focus on the bottom of trench but also gathers in the top of trench and the edge of super junction, therefore the distributions of the high electric field is more uniform, and thus to substantially improve the breakdown voltage (BV). By using the floating trench, the area of schottky contact is enlarged, thus the density of current is increased in the on state, and the specific on-resistance (Ron,sp) of the device is ultimately decreased. The results of simulation show that the BV and Ron,sp of S-FT SJ JBS diode are 1891V and 0.16 mΩ cm2, and the BV is improved by 29.5% and the Ron,sp is decreased by 50% compared with I-FT SJ JBS diode. The Baliga figure-of-merit (BFOM) of S-FT SJ JBS diode is 894 W·cm−2 which is increased by 236.1% compared with I-FT SJ JBS diode.

Hybrid ZnO:Ag core-shell nanoparticles for wastewater treatment : Growth mechanism and plasmonically enhanced photocatalytic activity

Finely dispersed ZnO (core):Ag (shell) nanostructures were prepared following a simple two-step chemical process. The technique allowed a precisely controlled thin surface coating of Ag, and offers a convenient way for surface functionalization of the ZnO nanoparticles. Substantial improvement in the UV emission confirms intense excitation of the surface plasmons supported by a highly effective metal-semiconductor interfacing in the ZnO:Ag hybrid nanostructures. Besides, the surface modification radically enhanced the light-induced catalytic activity of the ZnO nanoparticles. The superior photocatalytic performance was accredited to the Schottky barrier junctions formed between the ZnO core and Ag shell, which efficiently facilitates the separation of electrons (e−) and holes (h+), and formation of reactive oxygen species. Photocatalytic degradation of chemical dyes was studied to evaluate the usefulness of the developed samples for wastewater treatment. A possible charge transfer mechanism to elucidate the improvement in the photocatalytic activity was also discussed.

4H-SiC 1200 V Junction Barrier Schottky Diodes with High Avalanche Ruggedness

A state-of-the art family of 1200 V junction barrier Schottky (JBS) diodes was developed. These devices are highly competitive in switching applications thanks to low specific series resistance (1.8 mΩ.cm2 at current rating) and low capacitive charge (1420 nC.cm-2 at 800 V). A uniform avalanche distribution over the active area combined with an optimized high-voltage termination provides industry-leading UIS capabilities. Stringent reliability tests were performed to meet the qualification requirements for the industrial market.