Power Schottky 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.

Reverse characterization prediction of diamond Schottky barrier power devices using machine learning: Predicting breakdown voltage and Baliga figure of merit

Diamond power devices showed great potential for high-performance and low-loss applications at high frequencies. Schottky power diodes on the diamond have markedly higher threshold reverse operation limits than other power devices, yet they are still far from the ideal limit. Therefore, utilizing the device capabilities across optimizing device parameters is severely time- and resource-intensive considering traditional trial-and-error experimental methodology. On the other hand, data-driven techniques can accelerate device optimization and reduce resource consumption. This work demonstrates machine learning models that predict breakdown voltage in addition to Baliga's power figure of merit (BFOM) for the first time. An experimentally driven dataset is constructed because of its reliability, precision, and potential for generalization. This dataset contains current-voltage characteristics raw data for more than 400 devices fabricated on heteroepitaxial diamond. Four machine learning algorithms are explored and evaluated based on 5-fold cross-validation to prevent overfitting. The extra-tree model shows the highest performance that accurately predicts the breakdown voltage, and the BFOM with R2 equal to 0.924 and 0.911, respectively. Additionally, it showed robust prediction accuracy on unseen data with an 8 % average relative error of 16 devices. Achieving this high accuracy indicates the potential of these models for generalization on various datasets.

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.

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.

Thick crack-free {113} epitaxial boron-doped diamond layers for power electronics—Deposition with nitrogen addition and high microwave power

In this work, first, we investigate the effect of nitrogen addition in microwave plasma enhanced chemical vapor deposition on the growth of thick {113} epitaxial diamond layers. We identify a narrow range of nitrogen concentrations for the growth of crack-free thick epitaxial layers with a smooth surface morphology. Without nitrogen, cracks start to appear after a layer thickness of 7–10 μm due to elastic energy stored in the epitaxial layer, but the addition of nitrogen stabilizes layer growth. We also investigate the use of low microwave power density growth conditions to produce thick boron-doped epitaxial layers. We observe a very high boron incorporation efficiency using these growth conditions. Finally, we demonstrate the fabrication of a thick (>200 μm) {113} p+ monocrystal plate. The concentration of boron in heavily doped diamond with metallic conductivity has been investigated by the Hall effect measurement technique, Raman spectroscopy, and secondary ion mass spectroscopy. The growth of high quality thick {113} oriented epitaxial layer with high boron concentration (>1020 cm−3) and low resistivity and the fabrication for the freestanding p+ substrates are necessary steps for the fabrication of vertical electronic devices such as high power Schottky diodes.

Investigation of Electrically Active Defects in SiC Power Diodes Caused by Heavy Ion Irradiation

Deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) are used to investigate electrically active defects in commercial SiC Schottky power diodes after heavy-ion microbeam irradiation at different voltages. The DLTS and MCTS spectra of pristine samples are analysed and compared to devices showing or not signatures of Single Event Leakage Current (SELC) degradation. An additional peak labelled ‘C’ with an activation energy of 0.17 eV below the conduction band edge is observed in the DLTS spectra of a sample degraded with SELC.

A self-aligned Ga2O3 heterojunction barrier Schottky power diode

We report an alignment-free gallium oxide (Ga2O3) heterojunction barrier Schottky (HJBS) power diode, which utilizes the self-assembled Ni nanostructures as in situ masks for the trench etching of Ga2O3 and the subsequent selective-area filling of p-type NiO. By increasing the trench depth to 200 nm, the relevant HJBS diode exhibits improved reverse blocking capabilities including the reduced leakage current density of 10−8 A/cm2 (at a reverse bias of 100 V) and the enhanced breakdown voltage of 748 V, while maintaining the forward biasing characteristics similar to the Schottky barrier diode (SBD). The variation of turn-on voltage and the reverse breakdown features indicate the conversion of the HJBS diodes characteristics from Ni/Ga2O3 SBD to the NiO/Ga2O3 p-n heterojunction diode. The electrical field simulations and experimental facts imply that the remarkable lateral pinch-off effect in the 200-nm trenched diodes shields the electric field in the depletion region underneath the Ni/Ga2O3 Schottky contact. This work provides a straightforward strategy to simplify the fabrication process of Ga2O3-based HJBS diodes with both promising forward and reverse performances.

Silicon Carbide Power Devices: Progress and Future Outlook

Silicon Carbide (SiC) power devices have become commercialized and are being adopted for many applications after 40 years of effort to produce large diameter wafers and high performance device structures. This paper provides a historical perspective of the key breakthroughs that were needed to make progress towards this goal. The JBS rectifier concept was a critical innovation required to make SiC power Schottky rectifiers viable. The Baliga-Pair or Cascode concept was an intermediate step to realize a practical SiC power switch in the 1990s. An essential unique innovation created in the 1990s was the shielded planar SiC power MOSFET structure that is now commonly used for commercial products. Shielded trench-gate SiC power MOSFETs were also proposed in the 1990s which led to commercial products in the last 5 years. Although achieving a low specific on-resistance in SiC power MOSFETs was essential at the inception of the technology, its penetration into power electronics applications is now driven by performance metrics for high frequency circuits. Device structural enhancements to improve the high frequency figures-of-merit are described that have led to major strides in performance. This includes the JBSFET concept where a JBS diode is integrated into the MOSFET structure to suppress current flow through the body diode; the SG and BG MOSFET structures which reduce the gate-drain charge; and the OCTFET structure where the gate-drain overlap area is reduced. Future developments in SiC power devices include increasing the blocking voltage rating to expand the applications spectrum. In addition, a SiC monolithic bi-directional switch has been demonstrated to allow implementation of matrix converters; and a SiC monolithic reverse blocking switch has been demonstrated to allow deployment of current source inverters.

Ultrafast GaAs MOVPE growth for power electronics

Schottky diodes designed with negative breakdown voltages of up to 400 V are used in applications like power supplies, motor drives, battery charging and server/data centers. GaAs is an ideal choice for such devices. Due to its high electron mobilities, lower series resistance and thus lower power consumptions in the “on” state than using Si, GaN or SiC can be achieved. Also GaAs wafers are available up to 8” with extremely high quality and low etch pit densities. To achieve breakdown voltages above 200 V in GaAs, typically doping levels below 1*1015 cm−3 and thicknesses in the range of tens of micrometers are needed. In order to achieve minimum turn-on losses, the thickness and doping has to be precisely controlled. For the epitaxy, the process time and group V precursor consumption due to typically high V/III ratios are the two largest cost factors. Recently, we have introduced MOVPE processes on a close coupled CRIUS showerhead reactor with growth rates up to 280 µm/h. Due to the extremely high growth rate, the loss of group-V material due to evaporation off the growth surface is minimized and even at V/III ratios below 15 a low C-background doping can be achieved. It is demonstrated that this low cost and ultrafast growth process is suitable for Schottky power diodes. 15 µm thick GaAs:Si Hall samples were grown at a growth rate of 100 µm/h. Controlled n-doping levels as low as 1.2*1014 cm−3 have been reached for a V/III ratio of 12. The room temperature mobilities were as high as 9*103 cm−3/Vs. Also, the electronic defect levels were analyzed by deep level transient spectroscopy. The EL2 (As anti-site) defect is found with a concentration 4.8*1014 cm−3. Nominally 20 µm and 30 µm thick layers were deposited on n-GaAs wafers for initial Schottky test diodes. The I-V curve in forward characteristics is characterized by an ideality factor of 1.2, a Schottky barrier height of 0.8 eV and a series resistance as low as 3.7 mΩcm2. Breakdown voltages above 370 V in reverse bias for doping levels of 2*1014 cm−3 were achieved proving the high potential of this approach.

A 135–150 GHz High-Power Frequency Tripler With Filtering Matching Network

This letter presents a 135–150 GHz high-efficiency and -power Schottky diode-based tripler integrated with low-loss waveguide filtering matching network. The active diode monolithic microwave integrated circuit (MMIC) is matched with two waveguide filters based on coupling matrix theory for a two-port network with complex impedance terminations. The filters and the active diode MMIC are integrated via the microstrip-to-waveguide transition, allowing a compact design on the relatively higher loss MMIC. In addition, an integrated on-chip capacitor is implemented to isolate dc and RF paths. The measurement shows that with 150–200 mW input power, the maximum conversion efficiency reaches 30.5% and the maximum output power is 47 mW. All filtering poles can be observed in measurements and the return loss achieves 10–15 dB within the passband. Good agreements between measurements and simulations demonstrate the validity of the design approach.

Numerical analysis of the GaN trench MIS barrier Schottky diodes with high dielectric reliability and surge current capability

The commercialization of GaN-based Schottky barrier diodes in middle- and high- voltage applications still faces many challenges, in which the lack of an effective selective area p-type doping method is one of the main obstacles. This paper proposes novel vertical GaN-based Schottky diodes with trench MIS structure and an embedded p-GaN protection layer (junction-trench MIS barrier Schottky diodes, J-TMBS). The trench structure and lateral p-n junctions can be achieved by selectively etching the very thin p-GaN and then regrowing n-GaN. Therefore, the fabrication technology avoids the selective area p-type doping process, and the dry etching damage and poor sidewall regrowth interface issue, which are serious in GaN Merged pn/Schottky (MPS) diodes, can also be alleviated for the proposed J-TMBS. Compared with the optimized GaN trench MIS barrier Schottky (TMBS) diodes, the surge current capability and dielectric reliability of the proposed J-TMBS are significantly improved (the electric field of the dielectric layer and maximum lattice temperature under the surge test can be reduced by 448% and 202%, respectively). In addition, the specific on-resistance (Ron,sp) and breakdown voltage remain basically unchanged compared with TMBS. Compared with the optimized GaN MPS diodes, the proposed structure improves the specific on-resistance by 17.2% benefiting from the reduced area of the JFET region without degrading the reverse I–V characteristics and surge current capability. The proposed J-TMBS exhibits potential in practical high voltage (>600 V) application of GaN Schottky power diodes.

TCAD investigation of the transport of carriers deposited by alpha particles in silicon carbide power Schottky devices

Radioactive sources and spectroscopy techniques have been proposed in recent publications as an approach to sense the internal electric field and to assess the susceptibility of power semiconductors devices to terrestrial cosmic rays. In this paper, dedicated experiments and advanced TCAD tools are used to understand the formation and the collection of the charge pulses that are generated by alpha particles in SiC Schottky diodes. Special attention is paid to the processes leading to the multiplication of the carriers' species. It is shown that the charge multiplication process is strongly affected by the location of the interaction zone and on impinging angle of the ionizing particle, along with the biasing condition of the device.

Express method of electro-physical parameters extraction for power Schottky diodes

A detailed express procedure of basic electro-physical parameters determination for power Schottky diodes has been presented. The procedure was approved using commercial diodes based on 4H-SiC by CREE, Inc. It relies on the device physical model only and almost excludes the usage of experimental data as the initial calculation parameters. During the calculation procedure the information available in the device datasheet is mainly used. If necessary, it may be supplemented by simple C-V and I-V characterization data of the device. The calculation technique is remarkable for its ability to extract electro-physical parameters of Schottky diodes with high accuracy and reliability. This is due to both: the usage of analytical equations instead of mathematical processing of the device characterization data presented graphically as well as the implementation of reliability control of obtained electro-physical parameters by calculating on their basis already known characteristics and parameters given in the datasheet or in the literature. The results of this work could promote the development of power Schottky and p-i-n diode operation theory at high temperatures.

Response of electron-irradiated silicon carbide Schottky power diodes at elevated temperature

Thermal-dependence experiments were executed on silicon carbide Schottky diodes. Devices were exposed to 3 MeV electrons with 10 MGy dose. Current density-voltage (~300 K to ~490 K) characterisation was used for investigation. At highest tested temperature, forward current at 0.3 V increased approximately seven orders of magnitude for unirradiated; and eight orders of magnitude for irradiated devices due to free carriers generation which obtained energy from the temperature. Series resistance of unirradiated increased with increasing temperature due to decrease in free carriers mobility, whilst irradiated devices decreased with increasing temperature which indicates that more free carriers acquired enough energy to escape the radiation-induced traps. Reverse current increased with increasing temperature due to the radiation-induced defects that act as generation-recombination centres. Activation energies of irradiated is higher than unirradiated devices. Also, there are two slopes in the plot of the activation energy-voltage which suggests that the reverse leakage current is due to two different mechanisms.

Response of electron-irradiated silicon carbide Schottky power diodes at elevated temperature

Thermal-dependence experiments were executed on silicon carbide Schottky diodes. Devices were exposed to 3 MeV electrons with 10 MGy dose. Current density-voltage (~300 K to ~490 K) characterisation was used for investigation. At highest tested temperature, forward current at 0.3 V increased approximately seven orders of magnitude for unirradiated; and eight orders of magnitude for irradiated devices due to free carriers generation which obtained energy from the temperature. Series resistance of unirradiated increased with increasing temperature due to decrease in free carriers mobility, whilst irradiated devices decreased with increasing temperature which indicates that more free carriers acquired enough energy to escape the radiation-induced traps. Reverse current increased with increasing temperature due to the radiation-induced defects that act as generation-recombination centres. Activation energies of irradiated is higher than unirradiated devices. Also, there are two slopes in the plot of the activation energy-voltage which suggests that the reverse leakage current is due to two different mechanisms.

Commercialization of Highly Rugged 4H-SiC 3300 V Schottky Diodes and Power MOSFETs

In this paper, we present a new family of 3300 V silicon carbide (SiC) Schottky barrier diodes (SBDs) and power MOSFETs. The main design requirements are discussed with an emphasis on the design rules to improve the long-term reliability. Basic static and dynamic performance demonstrates low conduction and switching losses. Long-term tests such as high-temperature reverse bias (HTRB) and body diode forward bias stress were performed to evaluate the devices’ reliability. An emission microscopy (EMMI) study was conducted to assess the quality of the gate oxide. Outstanding surge and avalanche capabilities are reported with UIS ruggedness of 11.4 and 20.8 J.cm-2 for SBDs and MOSFETs, respectively.

Impact of Electron Radiation Dose to the Performance of Half-Wave Rectifier and Converter Circuits with Silicon Carbide Schottky Diode

Half-wave rectifier; buck; and boost converter with electron-irradiated, high-voltage silicon carbide Schottky power diodes from CREE, Inc., performance were studied and presented in this paper subjected to electron radiation. The diodes were irradiated by high-energy (3 MeV) electrons with doses ranging from 1 to 5 MGy. The performance of the circuits in term of the output voltage were measured before and after the diodes being irradiated. It was observed, at 4 MGy, the half-wave rectifier output voltage degrades by 6.2 times as compared to before irradiation. Meanwhile, the output voltage of the buck converter degrades by 1.7 times; and for boost converter, the degradation of the output voltage is approximately 4.6 times for 4MGy radiation. These degradations are believed to be due to the increase in the series resistance of the Schottky diodes which is caused by the defects introduced inside the semiconductor during the irradiation and also the increase of turn-on voltage of the diodes after being irradiated.

Energy Efficient Computing and Electronics: Devices to Systems [Book News

This book discusses how to design energy-efficient electronic devices, circuits, and systems in the quest to lower computing energy consumption per bit. This timely book is divided into three sections, each including five chapters. The first section is devoted to emerging low-power devices that are able to obtain energy-efficient device structures. Section II is devoted to loss reduction in sensors, interconnects, and gallium nitride (GaN) Schottky power diodes. And Section III addresses aspects of systems design and related applications. The book is also a valuable tool for graduate-level teachers and practicing professionals who need to understand and master energy-efficient revolutionary device concepts, associated circuits, and architectures that may greatly extend the practical engineering limits of future energyefficient computation from device to system level.

Unifying Concepts for Ion-Induced Leakage Current Degradation in Silicon Carbide Schottky Power Diodes

The onset of ion-induced reverse leakage current in SiC Schottky diodes is shown to depend on material properties, ion linear energy transfer (LET), and bias during irradiation, but not the voltage rating of the parts. This is demonstrated experimentally for devices from multiple manufacturers with voltage ratings from 600 to 1700 V. Using a device with a higher breakdown voltage than required in the application does not provide increased robustness related to leakage current degradation, compared to using a device with a lower voltage rating.

Radiation Defects Created in n‐Type 4H‐SiC by Electron Irradiation in the Energy Range of 1–10 MeV

Radiation damage produced in 4H‐SiC n‐epilayers by electrons of different energies is presented. Junction barrier Schottky power SiC diodes are irradiated with 1.05, 2.1, 5, and 10 MeV electrons with doses up to 600 kGy. Radiation defects are characterized by capacitance deep‐level transient spectroscopy and capacitance‐to‐voltage (C–V) measurement. Results, which are compared with previous data obtained on 4.5 MeV electrons, show that the damage structure is very similar for all irradiation energies. Dominating is the generation of simple, thermally unstable defects evidenced by the presence of acceptor levels located at 0.25, 0.38, 0.60, and 0.72 eV below the 4H‐SiC conduction band edge. With increasing energy of electrons, the number of simple defects saturates, and the production of more complex, cluster‐related defects grow. Majority of introduced defects are acceptor centers, which compensate n‐type (nitrogen) doping of the epilayer. The carrier removal rate increases with electron energy and follows well the classical nonionization energy loss (NIEL) scaling for electrons in silicon. The stability of introduced defects and their effect on carrier lifetime reduction are discussed, as well.