Leakage currents in 4H-SiC JBS diodes

Leakage currents in high-voltage 4H-SiC diodes, which have an integrated (p-n) Schottky structure (Junction Barrier Schottky, JBS), have been studied using commercial diodes and specially fabricated (based on a commercial epitaxial material) test Schottky diodes with and without the JBS structure. It is shown that (i) the main role in reverse charge transport is played by SiC crystal structure defects, most probably, by threading dislocations (density ∼10⁴ cm⁻²), and (ii) the JBS structure, formed by the implantation of boron, partially suppresses the leakage currents (by up to a factor of 10 at optimal separation, 8 μm between local p-type regions).     

Estimation of the energy characteristics of the 3C-SiC/2H-, 4H-, 6H-, and 8H-SiC heterojunctions

Based on the assumption that the electron affinity of the SiC polytypes is linearly dependent on the degree of hexagonality, the offsets of the conduction band and valence band at the point of contact between the cubic 3C-SiC polytype and the hexagonal NH-SiC (N = 2, 4, 6, and 8) polytypes are determined. In the model of a triangular quantum well, the energy of the ground state, ε₀, is estimated. It is shown that the position of the energy level ε₀ can be adequately controlled only by doping the wide-gap n-NH-SiC polytype with shallow donors. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 39, No. 12, 2005, pp. 1440–1442. Original Russian Text Copyright ? 2005 by Davydov, Lebedev, Posrednik.     

The problem of uniformity of properties of 4H-SiC CVD films

Nonuniformities of electrical properties of 4H-SiC CVD films have been revealed using physicochemical reactions occurring upon introduction of radiation-induced structural defects. Primary knocked-on atoms and vacancies actively interact with impurities and defects of the starting material and thereby form the final system of radiation centers. The samples were irradiated with 900-keV electrons and 8-MeV protons at doses not leading to conductivity compensation (<7.5 × 10¹² cm⁻²) and a dose of 6 × 10¹⁴ cm⁻² causing deep compensation. Despite their area-averaging nature, capacitance methods demonstrated that characteristics of samples ∼3 mm in size are not identical. The nuclear spectrometry technique, which enables microprobing of samples, demonstrated individual behavior of separate parts of a film with areas of tens of square micrometers.     

High-voltage (3 kV) UMOSFETs in 4H-SiC

Vertical trench-gate metal-oxide-semiconductor field-effect transistors (UMOSFETs) in 4H-SiC having both trench oxide protection and junction termination extension (JTE) are reported for the first time. Devices are fabricated with and without counter-doped channels. Blocking voltages and specific on-resistances are 3360 V and 199 mΩ-cm² for doped-channel FETs and 3055 V and 121 mΩ-cm² for FETs without doped channels. These blocking voltages are the highest reported to date for UMOSFETs in SiC     

High-voltage (>1 kV) SiC Schottky barrier diodes with lowon-resistances

Au/6H-SiC Schottky barrier diodes with high blocking voltages were fabricated using layers grown by step-controlled epitaxy. A breakdown voltage of over 1100 V was achieved for silicon carbide (SIC) Schottky barrier diodes. These high-voltage SIC rectifiers had specific on-resistances lower than the theoretical limits of Si rectifiers by more than one order of magnitude. The specific on-resistance increased with temperature according to a T^2.0 dependence. The diodes showed good characteristics at temperatures as high as 400°C     

Behaviour of 1.2 kV SiC JBS diodes under repetitive high power stress

A methodology and a dedicated test-bench to evaluate the behaviour of SiC JBS diodes under repetitive high power stresses and surge currents have been developed and illustrated with JBS and Schottky 1.2 kV SiC diodes. The concept of dissipated energy versus the number of cycles is introduced to characterize the degradation evolution of the tested device. The sweeping current pulse technique offers the possibility to evaluate the effect of the self-heating on the I (V). This is especially relevant for JBS SiC diodes whose series resistance highly depends on the junction temperature. JBS diodes show a ×2.66 (×4.16) higher surge current capability at 25 °C (225 °C) than the pure Schottky diodes. The fabricated SiC JBS and Schottky diodes have been submitted to more than 300,000 power cycles at a dissipated energy of 0.7 J, showing no relevant degradation.     

采用浮空场限制环的耐压10kV碳化硅二极管的开发

The design, fabrication, and electrical characteristics of the 4H-SiC JBS diode with a breakdown voltage higher than 10 kV are presented. 60 floating guard rings have been used in the fabrication. Numerical simulations have been performed to select the doping level and thickness of the drift layer and the effectiveness of the edge termination technique. The n-type epilayer is 100 μm in thickness with a doping of 6 × 10^14 cm^-3. The on-state voltage was 2.7 V at JF = 13 A/cm^2.     

Effect of crystallographic defects on the reverse performance of 4H-SiC JBS diodes

A quantitative analysis of the effect of crystallographic defects on the performance of 4H-SiC junction barrier Schottky (JBS) diodes was performed. It has been shown that higher leakage current in diodes is associated with a greater number of elementary screw dislocations. Further, threading dislocation pair arrays were observed in some of the fabricated devices and, for the first time, the role of such defects on JBS reverse leakage currents is investigated.     

Consideration of spontaneous polarization in the problem of NH-SiC/3C-SiC/NH-SiC heterostructures formed by cubic (3C) and hexagonal (NH) silicon carbide polytypes

The problem of three-layer NH-SiC/3C-SiC/NH-SiC heterostructures was considered within the model previously proposed for describing the heterojunction between NH-SiC/3C-SiC silicon carbide polytypes, taking into account spontaneous polarization of hexagonal regions. The potential in the cubic 3C region was approximated by a model function constructed from physical considerations. Much attention was paid to the study of the effect of spontaneous polarization and the 3C region thickness on energy characteristics of quantum wells formed near heterojunctions. Original Russian Text ? S.Yu. Davydov, A.V. Troshin, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 10, pp. 1211–1217.     

3300V 4H-SiC MOSFET 设计与加工

成功设计并制造了击穿电压超过3300V 的4H-SiC MOSFET。通过数字仿真优化了漂移层和DMOSFET有源区参数。漂移层N型外延厚度为33微米并且掺杂浓度为2.5E15cm-3。器件采用浮空场限制环作为终端。当栅极电压为20V,漏极电压为2.5V时,漏极电流为5A。     

Experimental 4<Emphasis Type="Italic">H</Emphasis>-SiC junction-barrier Schottky (JBS) diodes

4H-SiC junction-barrier Schottky (JBS) diodes have been fabricated with local p–n junctions under the Schottky contact formed by nonequilibrium diffusion of boron. Static and dynamic characteristics of the JBS diodes are compared with those of similar 4H-SiC Schottky diodes. It is shown that, compared with ordinary Schottky diodes, the JBS diodes have leakage currents that are, on average, a factor of 200 lower at the same reverse bias. The reverse recovery charge is the same for both types of diodes and equal to the charge of majority carriers removed from the n-type base region in switching.     

A 2-dimensional fully analytical model for design of high voltage junction barrier Schottky (JBS) diodes

A physics-based closed form analytical model for the reverse leakage current of a high voltage junction barrier Schottky (JBS) diode is developed and shown to agree with experimental results. Maximum electric field “seen” by the Schottky contact is calculated from first principles by a 2-dimensional method as a function of JBS diode design parameters and confirmed by numerical simulations. Considering thermionic emission under image force barrier lowering and quantum mechanical tunneling, electric field at the Schottky contact is then related to reverse current. In combination with previously reported forward current and resistance models, this gives a complete I-V relationship for the JBS diode. A layout of interdigitated stripes of P-N and Schottky contacts at the anode is compared theoretically with a honeycomb layout and the 2-D model is extended to the 3-D honeycomb structure. Although simulation and experimental results from 4H-Silicon Carbide (SiC) diodes are used to validate it, the model itself is applicable to all JBS diodes.     

High-voltage 4H-SiC PiN diodes with the etched implant junction termination extension

This paper presents the design and fabrication of an etched implant junction termination extension(JTE) for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multiple etching steps to achieve the optimum JTE concentration range. The simulation results show that the etched implant JTE method can improve the blocking voltage of SiC PiN diodes and also provides broad process latitude for parameter variations, such as implantation dose and activation annealing condition. The fabricated SiC PiN diodes with the etched implant JTE exhibit a highest blocking voltage of 4.5 kV and the forward on-state voltage of 4.6 V at room temperature. These results are of interest for understanding the etched implant method in the fabrication of high-voltage power devices.     

Analytical Modeling of High-Voltage 4H-SiC Junction Barrier Schottky (JBS) Rectifiers

We develop a new analytical model for the junction barrier Schottky (JBS) rectifier and apply it to high-voltage 4H-SiC JBS rectifiers. This model uses a novel method to approximate the electric field at the Schottky contact, which is together with the Fowler–Nordheim tunneling equation to accurately calculate the reverse leakage current of a high-voltage 4H-SiC JBS rectifier. The forward on-resistance of a high-voltage 4H-SiC JBS rectifier consists of several components, which are dominated by the spreading resistances in the drift layer. Moreover, this model has been verified by comparing the simulation and experimental results, and they are shown to be in good agreement.      

Ruggedness analysis of 3.3 kV high voltage diodes considering various buffer structures and edge terminations

Buffer structures and edge termination have a decisive influence on the static and dynamic characteristics of free-wheeling diodes. In this paper the influence of buffer structures at the cathode side, the influence of the design of the edge termination and of a resistive zone at the anode side are analysed with respect to the ruggedness of free-wheeling diodes. Therefore, we investigated the device behaviour by means of numerical device simulation concerning the formation of current filamentation and the correlated shape of the electrical field distribution. The considered edge termination of the diodes was planar junction termination extensions and a beveled edge. Various buffer structures, a Gaussian buffer and a buried n-doped layer of increased doping called epitaxy level buffer are compared with a reference diode without any buffer structure.     

3.3 kV 4H-SiC DMOSFET with a source-contacted dummy gate for high-frequency applications

In this paper,a 4H-SiC DMOSFET with a source-contacted dummy gate(DG-MOSFET)is proposed and analyzed through Sentaurus TCAD and PSIM simulations.The source-contacted MOS structure forms fewer depletion regions than the PN junction.Therefore,the overlapping region between the gate and the drain can be significantly reduced while limiting RON degradation.As a result,the DG-MOSFET offers an improved high-frequency figure of merit(HF-FOM)over the conventional DMOSFET(C-MOSFET)and central-implant MOSFET(CI-MOSFET).The HF-FOM(RON×QGD)of the DG-MOSFET was improved by 59.2％and 22.2％compared with those of the C-MOSFET and CI-MOSFET,respectively.In a double-pulse test,the DG-MOSFET could save total power losses of 53.4％and 5.51％,respectively.Moreover,in a power circuit simulation,the switching power loss was reduced by 61.9％and 12.7％in a buck converter and 61％and 9.6％in a boost converter.     

10A/600V大功率硅基JBS肖特基二极管的制备

为了弥补传统肖特基二极管漏电流大和反向耐压低的不足,采用栅条P+-N结和肖特基结嵌套形成结势垒肖特基二极管(JBS),终端结构由7道场限环和1道切断环构成。通过模拟确定最优参数后流片试验,同步制备肖特基二极管(SBD)和Pi N二极管作为对比。结果表明:制备的JBS二极管兼备SBD二极管正偏和Pi N二极管反偏的优点。在漏电流密度小于1×10-5A/cm2时,反向耐压达到600 V;正向电流10 A(80.6 A/cm2)时,导通压降仅为1.1V。     

Analysis of junction-barrier-controlled Schottky (JBS) rectifier characteristics

This paper provides analytical solutions for the forward conduction and reverse leakage characteristics of junction-barrier-controlled Schottky (JBS) rectifiers. Good agreement between the calculated output characteristics using these solutions and experimental measurements on devices fabricated with different junction depths and Schottky barrier heights is observed. These equations are valuable for the analysis and design of JBS power rectifiers.     

High power 4H–SiC pin diodes (10 kV class) with record high carrier lifetime

The hole lifetime τ_p in the n-base and isothermal (pulse) current–voltage characteristics have been measured in 4H–SiC diodes with a 10 kV blocking voltage (100 μm base width). The τ_p value found from open circuit voltage decay (OCVD) measurements is 3.7 μs at room temperature. To the best of the authors’ knowledge, the above value of τ_p is the highest reported for 4H–SiC. The forward voltage drops V_F are 3.44 V at current density j = 100 A/cm² and 5.45 V at j = 1000 A/cm². A very deep modulation of the blocking base by injected non-equilibrium carriers has been demonstrated. Calculations in term of a simple semi-analytical model describe well the experimental results obtained.     

Ion implantation of platinum from pulsed laser plasma for fabrication of a hydrogen detector based on an n-6H-SiC crystal

A fairly simple method of surface doping of a SiC substrate with a catalytic metal (in particular, platinum) from a pulsed laser plasma is suggested. Doping is attained due to implantation of high-energy ions and ion mixing of the plasma-deposited film with the surface layer of the SiC substrate. The developed mathematical model makes it possible to conduct predictive calculations of the energy spectrum of implanted platinum ions on the basis of experimental data on the main physical characteristics of the pulsed laser plasma and technical parameters of the high-voltage system. The study of ion-implanted layers in the n-6H-SiC crystals have revealed features of structural and phase variations in the surface layers of the crystal at various doses of “hot” (600°C) ion implantation. On the basis of an analysis of experimental data, it is suggested that there are different solid-state reactions of platinum with silicon carbide in relation to the dose of implantation; these reactions cause a loss or acquisition of catalytic properties of nanosystems in the formation of platinum silicides or metal-like clusters, respectively. Optimization of the dose of ion implantation of platinum makes it possible to fabricate an on-chip n-6H-SiC structure, which varies the electrical parameters in a hydrogen-containing environment at elevated temperatures.