Analytical model for reverse characteristics of 4H-SiC merged PN-Schottky （MPS） diodes

A new analytical model for reverse characteristics of 4H--SiC merged PN--Schottky diodes (MPS or JBS) is developed. To accurately calculate the reverse characteristics of the 4H--SiC MPS diode, the relationship between the electric field at the Schottky contact and the reverse bias is analytically established by solving the cylindrical Poisson equation after the channel has pinched off. The reverse current density calculated from the Wentzel--Kramers--Brillouin (WKB) theory is verified by comparing it with the experimental result, showing that they are in good agreement with each other. Moreover, the effects of P-region spacing (S) and P-junction depth (X_j) on the characteristics of 4H--SiC MPS are analysed, and are particularly useful for optimizing the design of the high voltage MPS diodes.     

Simulation research on offset field-plate used as edge termination in 4H-SiC merged PiN-Schottky diodes

A new structure of 4H--silicon carbide (SiC) merged PiN-Schottky (MPS) diodes with offset field-plate (FP) as edge termination is developed. To understand the influences of 4H--SiC MPS diodes with offset FP on the characteristics, simulations have been done by using ISE TCAD. Related factors of offset FP have been studied as well to optimise the reverse characteristics of 4H--SiC MPS diodes. The simulation results show that the device using offset FP can create a higher blocking voltage under reverse bias as compared with that using field guard rings. Besides, the offset FP does not cause any extra steps in the manufacture of MPS diodes.     

First-principle calculation on the defect energy level of carbon vacancy in 4H--SiC

First, electronic structures of perfect wurtzite 4H-SiC were calculated by using first-principle ultra-soft pseudo- potential approach of the plane wave based on the density functional theory; and the structure changes, band structures, and density of states were studied. Then the defect energy level of carbon vacancy in band gap was examined by substituting the carbon in 4H-SiC with carbon vacancy. The calculated results indicate the new defect energy level generated by the carbon vacancy, and its location in the band gap in 4H-SiC, which has the character of deep acceptor. A proper explanation for green luminescence in 4H-SiC is given according to the calculated results which are in good agreement with our measurement results.     

Model and analysis of drain induced barrier lowering effect for 4H--SiC metal semiconductor field effect transistor

Based on an analytical solution of the two-dimensional Poisson equation in the subthreshold region, this paper investigates the behavior of DIBL (drain induced barrier lowering) effect for short channel 4H--SiC metal semiconductor field effect transistors (MESFETs). An accurate analytical model of threshold voltage shift for the asymmetric short channel 4H--SiC MESFET is presented and thus verified. According to the presented model, it analyses the threshold voltage for short channel device on the L/a (channel length/channel depth) ratio, drain applied voltage V_DS and channel doping concentration N_D, thus providing a good basis for the design and modelling of short channel 4H--SiC MESFETs device.     

Numerical and experimental study of the mesa configuration in high-voltage 4H–SiC PiN rectifiers

The effect of the mesa configuration on the reverse breakdown characteristic of a SiC PiN rectifier for high-voltage applications is analyzed in this study.Three geometrical parameters,i.e.,mesa height,mesa angle and mesa bottom corner,are investigated by numerical simulation.The simulation results show that a deep mesa height,a small mesa angle and a smooth mesa bottom(without sub-trench) could contribute to a high breakdown voltage due to a smooth and uniform surface electric field distribution.Moreover,an optimized mesa structure without sub-trench(mesa height of 2.2 μm and mesa angle of 20°) is experimentally demonstrated.A maximum reverse blocking voltage of 4 kV and a forward voltage drop of 3.7 V at 100 A/cm~2 are obtained from the fabricated diode with a 30-μm thick N~- epi-layer,corresponding to 85% of the ideal parallel-plane value.The blocking characteristic as a function of the JTE dose is also discussed for the PiN rectifiers with and without interface charge.     

Sinusoidal Steady State Analysis on 4H--SiC Buried Channel MOSFETs

With the combined use of the drift-diffusion （DD） model, experiment measured parameters and small-signal sinusoidM steady-state analysis, we extract the Y-parameters for 4H-SiC buried-channel metal oxide semicon- ductor field effect transistors （BCMOSFETs）. Output short-circuit current gain G and Mason＇s invariant U are cMculated for extrapolating unity current gain frequency in the common-source configuration fT and the maximum frequency of oscillation fmax, respectively. Here fT = 800 MHz and fmax= 5 GHz are extracted for the 4H-SiC BCMOSFETs, while the field effect mobility reaches its peak value 87cm2/Vs when VGs = 4.5 V. Simulation results clearly show that the characteristic frequency of 4H-SiC BCMOSFETs and field effect mobility are superior, due to the novel structure, compared with conventional MOSFETs.     

结终端采用JTE保护技术的4H-SiC PiN二极管模拟和研制

利用二维器件模拟软件ISE-TCAD 10.0,对结终端采用结扩展保护技术的4H-SiC PiN二极管平面器件进行反向耐压特性的模拟,并获得许多有价值的模拟数据.依据所得的模拟数据进行此种二极管器件的研制.实验测试表明,此二极管的模拟优化数据与实验测试的结果一致性较好,4H-SiC PiN二极管所测得到的反向电压达1600 V,该反向耐压数值达到理想平面结的击穿耐压90%以上.     

Physical simulations and experimental results of 4H—SiC MESFETs on high purity semi-insulating substrates

In this paper we report on DC and RF simulations and experimental results of 4H--SiC metal semiconductor field effect transistors (MESFETs) on high purity semi-insulating substrates. DC and small-signal measurements are compared with simulations. We design our device process to fabricate n-channel 4H--SiC MESFETs with 100~μm gate periphery. At 30~V drain voltage, the maximum current density is 440~mA/mm and the maximum transconductance is 33~mS/mm. For the continuous wave (CW) at a frequency of 2~GHz, the maximum output power density is measured to be 6.6~W/mm, with a gain of 12~dB and power-added efficiency of 33.7％. The cut-off frequency (f_T) and the maximum frequency (f_max) are 9~GHz and 24.9~GHz respectively. The simulation results of f_T and f_max are 11.4~GHz and 38.6~GHz respectively.     

Two-dimensional analysis of the interface states effects on current gain for 4H－SiC bipolar junction transistor

This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H--SiC bipolar junction transistor (BJT). Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H--SiC BJT performance.     

Research on high-voltage 4H-SiC P-i-N diode with planar edge junction termination techniques

The planar edge termination techniques of junction termination extension (JTE) and offset field plates and field-limiting rings for the 4H-SiC P-i-N diode were investigated and optimized by using a two-dimensional device simulator ISE-TCAD10.0. By experimental verification, a good consistency between simulation and experiment can be observed. The results show that the reverse breakdown voltage for the 4H-SiC P-i-N diode with optimized JTE edge termination can accomplish near ideal breakdown voltage and much lower leakage current. The breakdown voltage can be near 1650 V, which achieves more than 90 percent of ideal parallel plane junction breakdown voltage and the leakage current density can be near 3 × 10-5 A/cm2.     

Study of a 4H-SiC epitaxial n-channel MOSFET

Epitaxial channel metal-oxide semiconductor field-effect transistors (MOSFETs) have been proposed as one possible way to avoid the problem of low inversion layers in traditional MOSFETs. This paper presents an equation of maximum depletion width modified which is more accurate than the original equation. A 4H--SiC epitaxial n-channel MOSFET using two-dimensional simulator ISE is simulated. Optimized structure would be realized based on the simulated results for increasing channel mobility.     

Improvement on peak-to-trough ratio of sampled fiber Bragg gratings with multiple phase shifts

Via a cascaded structure, the peak-to-trough ratio is considerably improved for sampled fiber Bragg gratings （SFBGs） based on multiple-phase-shift （MPS） technique. This cascaded filter is composed of two identical SFBGs which are inserted with the increasing or decreasing arrangement of phase shifts. With this inverse arrangement of MPS in grating design, the phase fluctuation of individual SFBG can be compensated, and as a result an excellent phase matching condition is realized. In this way, the peak-to- trough ratio in reflection spectra is improved from 6 to 12 dB when multiplication factor m = 4, and from 5dBto 10dBwhenm=8.     

Determining the Parameters of the Jahn–Teller Effect in Impurity Centers from Ultrasonic Experiments: Application to the ZnSe : Ni2+ Crystal

Physics of the Solid State - The earlier developed methodology of ultrasonic investigation for determining the parameters of the Jahn–Teller effect (JTE) in impurity centers in crystals is...     

Modified projective synchronization of a fractional-order hyperchaotic system with a single driving variable

In this paper, the modified projective synchronization (MPS) of a fractional-order hyperchaotic system is investigated. We design the response system corresponding to the drive system on the basis of projective synchronization theory, and determine the sufficient condition for the synchronization of the drive system and the response system based on fractional-order stability theory. The MPS of a fractional-order hyperchaotic system is achieved by transmitting a single variable. This scheme reduces the information transmission in order to achieve the synchronization, and extends the applicable scope of MPS. Numerical simulations further demonstrate the feasibility and the effectiveness of the proposed scheme.     

HT-7U装置极向场电源变流系统的研制

介绍了HT-7U极向场电源中所使用的变流系统,提出了一种新的四象限运行控制方法,解决了极向场电源设计和制造的难点。实现了15kA的有环流运行。     

Surface conductivity of cuprous-oxide rectifiers

The physical nature of the surface conductivity of cuprous-oxide rectifiers, the existence of which was indicated by the authors (Fizika tverdogo tela,2, 857, 1960) is investigated. It is shown that this effect is not caused by surface conductivity of the cuprous oxide, but is due to the presence of a conduction channel along the edge of the p-n junction. The effect of humidity and the vapors of various liquids on the surface conductivity of rectifiers is investigated. The results obtained are discussed and a mechanism to explain the presence of a conduction channel at the p-n junction of cuprous-oxide rectifiers is suggested.The authors gratefully acknowledge their indebtedness to S. M. Margolin and M. A. Mishin for making available the rectifiers used in the investigation.     

Simulation study of a mixed terminal structure for 4H-SiC merged PiN/Schottky diode

In this paper, a mixed terminal structure for the 4H-SiC merged PiN/Schottky diode (MPS) is investigated, which is a combination of a field plate, a junction termination extension and floating limiting rings. Optimization is performed on the terminal structure by using the ISE-TCAD. Further analysis shows that this structure can greatly reduce the sensitivity of the breakdown voltage to the doping concentration and can effectively suppress the effect of the interface charge compared with the structure of the junction termination extension. At the same time, the 4H-SiC MPS with this termination structure can reach a high and stable breakdown voltage.     

Effect of variable particle size reinforcement on mechanical and wear properties of 6061Al–SiCp composite

Abstract

The influence of reinforcement particle size variation plays a major role on the properties of Al–SiC_p composite. Therefore, this study aim to investigate the mechanical and wear performance of single particle size (SPS) and multiple particle size (MPS) Al–SiC_p composite prepared by stir casting process. The SPS comprises three categories; fine (15 μm), intermediate (40 μm) and coarse (80 μm) particle sizes and combination of the three sizes accounts for the MPS in the ratio 1:1:2, respectively. Oxidation of the SiC_p and addition of 1 wt% Mg during composite processing resulted to interface reaction products such as MgO (magnesium oxide) and MgAl₂O₄ (magnesium aluminate) which suppresses the potential formation of undesired Al₃C₄ (aluminium carbide). The study reveals that MPS composite improved the hardness and impact properties with enhanced wear performance compared to SPS composite. Characterization of the composite morphology and phases was performed using scanning electron microscope and X-ray diffraction analysis. This study provides an effective method of optimizing the properties of Al–SiC_p composite by integrating MPS with low volume fraction of reinforcement phase.     

Rectifying behavior in Coulomb blockades: charging rectifiers

We introduce examples of tunneling and diffusive, Coulomb-regulated rectifiers based on the Coulomb blockade formalism in discrete and continuum systems, respectively. Nonlinearity of the interacting dynamics profoundly enhances the inherent asymmetry of the devices by reducing the Hilbert space of accessible states. The discrete charging rectifier is structurally similar to hybrid molecular electronic rectifiers, while the continuum-charging rectifier is based on a model of ionic flow through a pore (ion channel) with an artificial branch. The devices are formally related to ratchet systems with spatial periodicity replaced by a winding number: the current.     

Study and optimal simulation of 4H-SiC floating junction Schottky barrier diodes’ structures and electric properties

This paper stuides the structures of 4H-SiC floating junction Schottky barrier diodes. Some structure parameters of devices are optimized with commercial simulator based on forward and reverse electrical characteristics. Compared with conventional power Schottky barrier diodes, the devices are featured by highly doped drift region and embedded floating junction layers, which can ensure high breakdown voltage while keeping lower specific on-state resistance, and solve the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with optimized structure parameter, the breakdown voltage can reach 4.36 kV and the specific on-resistance is 5.8 mΩ·cm2 when the Baliga figure of merit value of 13.1 GW/cm2 is achieved.