4H-SiC结型势垒肖特基二极管的制作与特性研究

本文设计制作了两种具有不同结构参数的4H-SiC结型势垒肖特基二极管,在制作过程中采用了两种制作方法：一种是对正电极上的P型欧姆接触进行单独制作,然后制作肖特基接触的工艺过程;另一种是通用的通过一次肖特基接触制作就完成正电极制作的工艺过程。器件制作完成后,通过测试结果比较了采用场限环作为边界终端与未采用边界终端的器件的反向特性,结果显示采用场限环有效地提高了该器件的击穿电压,减小了其反向电流。另外,测试结果还显示采用独立制作P型欧姆接触的工艺过程有效提高了4H-SiC结型势垒肖特基二极管的反向特性,其中P型欧姆接触的制作过程和结果也在本文中做出了详细叙述。     

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.     

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).     

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.     

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.     

300V以上硅基新型JBS肖特基二极管的制备

为了在保留传统肖特基二极管正向压降低、电流密度大优点的基础上,使其反向击穿电压提高到了300 v以上,我们采用硅材料做为衬底,肖特基结区采用蜂房结构,终端采用两道场限环结构加一道切断环结构,所制备的肖特基二极管在正向电流10A时,正向压降仅为0.79 V;同时在施加300 V反向电压时,反向漏电流在5μA以下.     

Study of 4H-SiC JBS Diodes Fabricated with Tungsten Schottky Barrier

Tungsten is a suitable metal contact for high-temperature applications. We fabricated 1.7-kV and 6-kV 4H-SiC junction barrier Schottky (JBS) diodes with a tungsten Schottky contact with different geometries, and their forward characteristics were measured up to 300°C. The 1.7-kV diodes exhibited unipolar conduction up to 6 V at 275°C, whereas 6-kV diodes showed ideal on-resistance, R _on. An optimized JBS design permits a higher breakdown voltage to be obtained than for the pure Schottky diode, with a reasonable increase (10%) of the on-resistance. Results demonstrate the feasibility of tungsten JBS diodes for fast-switching, high-voltage, and high-temperature applications.     

Bipolar Conduction Impact on Electrical Characteristics and Reliability of 1.2- and 3.5-kV 4H-SiC JBS Diodes

4H-SiC Junction Barrier Schottky (JBS) diodes (1.2 and 3.5 kV) have been processed using the same technology with two different layouts. From 4 A and for the whole temperature range, the 3.5-kV diodes exhibit a bipolar conduction independent of the layout. However, the behavior of the 1.2-kV diodes depends on the design. At 500 V–300 $^{circ}hbox{C}$, the leakage current is only 100 nA and 10 $muhbox{A}$ for the 3.5- and 1.2-kV diodes, respectively. The switch-off performances show a reverse peak current of only 50% of the nominal current at 300 $^{circ}hbox{C}$ for all JBS diodes. The JBS diodes have a surge current capability of around 80 A, two times higher than the Schottky diodes. DC electrical stresses are performed during 50 h, and all the 1.2-kV diodes exhibit no bipolar degradation. Nevertheless, some slight bipolar degradation is observed in 3.5-kV JBS diodes. Electroluminescence measurements exhibit the expansion of stacking faults in 3.5-kV diodes unlike in 1.2-kV diodes.      

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.     

1200V/100A高温大电流4H-SiC JBS器件的研制

基于SiC结势垒肖特基(JBS)二极管工作原理及其电流/电场均衡分布理论,采用高温大电流单芯片设计技术及大尺寸芯片加工技术,研制了1 200 V/100 A高温大电流4H-SiCJBS二极管.该器件采用优化的材料结构、有源区结构和终端结构,有效提高了器件的载流子输运能力.测试结果表明,当正向导通压降为1.60 V时,其正向电流密度达247 A/cm2(以芯片面积计算).在测试温度25和200℃时,当正向电流为100 A时,正向导通压降分别为1.64和2.50 V;当反向电压为1 200 V时,反向漏电流分别小于50和200μA.动态特性测试结果表明,器件的反向恢复特性良好.器件均通过100次温度循环、168 h的高温高湿高反偏(H3TRB)和高温反偏可靠性试验,显示出优良的鲁棒性.器件的成品率达70％以上.     

High-voltage (3.3 kV) 4H-SiC JBS diodes

High-voltage 4H-SiC junction-barrier Schottky (JBS) diodes have been fabricated and studied. The working area of the diodes (anode contact area) is 1.44 mm². At currents in the range from 10⁻¹¹ to 1.5 A, the forward current-voltage characteristic of the diodes is described in terms of the thermionic emission model, with the series resistance taken into account: Schottky barrier height Φ_B = 1.16 eV, ideality factor n = 1.01, and series resistance R _s = 2.2 Ω (32 mΩ cm²). The value of R _s is governed by the resistance of the blocking epitaxial n-base (impurity concentration N = 9 × 10¹⁴ cm⁻³, n-layer thickness d = 34 μm). The diodes can block a reverse voltage of at least 3.3 kV (with a leakage current at room temperature on the order of 1 μA). It is suggested that the leakage mechanism is associated with crystal lattice defects (dislocations) in SiC. It is shown that the reverse-recovery characteristics of the diodes are determined by the flow of a purely capacitive reverse current.     

4H-SiC SBD和JBS退火研究

在4H-SiC外延材料上制备了SBD和JBS器件,研究并分析了退火温度对这两种器件正反向特性的影响。结果表明,低于350℃退火可同时提高SBD和JBS的正反向特性。当退火温度高于350℃时,二者的正向特性都出现退化,SBD退化较JBS更为严重。JBS阻断电压随退火温度升高而增大,在退火温度高于450℃时增加趋势变缓。SBD阻断电压随退火温度升高先升后降,在500℃退火时达到一个最大值。可见一定程度的退火有助于提高4H-SiCSBD和JBS器件的正反向特性,但须考虑其对正反向特性的不同影响。综合而言,退火优化后JBS优于SBD器件性能。     

Reliability and micro-structural properties of GaAs Schottky diodes for submillimeter-wave applications

Whisker contacted GaAs Schottky barrier diodes are the standard devices for mixing and multiplier applications in the THz frequency range. This is mainly due to their minimum parasitics and mature technology. But with the decreasing size of the anode contact, which is required for operation at high frequencies (up to approx. 3 THz), the reliability and the micro-structural understanding of the Schottky barrier becomes increasingly important. This contribution presents new results concerning the reliability of Schottky diodes and the physical properties of small-area Schottky junctions, especially at low current densities. For these purposes a number of different Schottky diodes have been fabricated with different epilayer doping concentrations and anode diameters. Measured I/V characteristics show that the diode current deviates considerably from the ideal thermionic current behavior with decreasing diode diameter. This deviation shows an exponential dependence on the diode voltage and is a function of the doping concentration of the active layer. For a given doping concentration in the epi-layer and decreasing anode diameter, this phenomenon shifts the minimum of the ideality factor towards higher current densities. An explanation is given in terms of a difference of the cyrstallinity of the polycrystalline platinum films on the GaAs for decreasing SiO₂ aperture size in connection with a reduced Pt mobility in the electrolyte. The reliability of Schottky barrier diodes under thermal and electrical stress has been investigated on different THz Schottky diode structures. The results show that the barrier height and the ideality factor of the fabricated structures are not affected by thermal stress. Electrical stress induced by large forward currents up to a current density of 10 kA/mm² even leads to a slight increase of the barrier height and a reduction of the series resistance.     

Advanced High-Voltage 4H-SiC Schottky Rectifiers

This paper presents advanced 4H-SiC high-voltage Schottky rectifiers with improved performance when compared to conventional 4H-SiC Schottky rectifiers. Two types of 4H-SiC junction barrier Schottky (JBS) rectifiers have been explored. These rectifiers offer Schottky-like ON-state and fast switching characteristics, while their OFF-state characteristics have a low leakage current similar to that of the PiN junction rectifier. Planar 4H-SiC JBS rectifiers, with more than 1-kV blocking capability and orders of magnitude lower reverse leakage current than that of conventional SiC Schottky rectifiers, have been demonstrated. In addition, a novel device structure, called lateral channel JBS rectifier, was designed and experimentally demonstrated in 4H-SiC with up to 1.5-kV blocking capability and pinlike reverse characteristics.      

Active Micromachined Integrated Terahertz Circuits

Schottky barrier diodes have been integrated into on-chip rectangular waveguides. Two novel techniques have been developed to fabricate diodes with posts suitable for integration into waveguides. One technique produces diodes with anode diameters of the order of microns with post heights from 90 to 125 microns and the second technique produces sub-micron anodes with post heights around 20 microns. A method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.F. output in a mixer circuit. Devices have been fabricated and D.C. characterized.     

Comparison of GaN p-i-n and Schottky rectifier performance

The performance of GaN p-i-n and Schottky rectifiers fabricated on the same wafer was investigated as a function of device size and operating temperature. There was a significant difference in reverse breakdown voltage (490 V for p-i-n diodes; 347 V for the Schottky diodes) and forward turn-on voltage (~5 V for the p-i-n diodes; ~3.5 V for the Schottky diodes). Both types of device showed a negative temperature coefficient for reverse breakdown, with value -0.34±0.05 V·K^-1     

Low breakdown voltage Schottky diode as voltage regulator

Experimental evidence is given showing that Ag-n-Si Schottky diodes with resistivity about 40 m?cm have steeper reverse breakdown characteristics than corresponding low-voltage p-n junction regulator diodes fabricated by local epitaxy. Avalanche multiplication in such a diode starts at 1.7 V, and the device has a low positive temperature coefficient of breakdown voltage.     

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.      

Low-Temperature Annealing of Lightly Doped n-4H-SiC Layers after Irradiation with Fast Electrons

Semiconductors - The effect of low-temperature (up to 600°C) isothermal and isochronous annealing on the electrical characteristics of irradiated n-4H-SiC JBS Schottky diodes is studied....