Improved multi-recessed 4H–SiC MESFETs with double-recessed p-buffer layer

An improved multi-recessed 4H–SiC metal semiconductor field effect transistor (MRD-MESFET) with double-recessed p-buffer layer (DRB-MESFET) is proposed in this paper. By introducing a double-recessed p-buffer layer, the gate depletion layer is further modulated, and higher drain saturation current and DC transconductance are obtained compared with the MRD-MESFET. The simulations show that the drain saturation current of the DRB-MESFET is about 42.4% larger than that of the MRD-MESFET. The DC transconductance of the DRB-MESFET is almost 15% higher than that of the MRD-MESFET and very close to that of double-recessed structure (DR-MESFET) at the bias conditions of V_gs=0 V and V_ds=40 V. The proposed structure has an improvement of 26.1% and 74.2% in the output maximum power density compared with that of the MRD-MESFET and DR-MESFET, respectively. In the meanwhile, the proposed structure possesses smaller gate-source capacitance, which results in better RF characteristics.     

Structural,Electrical, and Optical Properties of 4H–SiC for Ultraviolet Photodetectors

Semiconductors - The results of investigations of initial n-4H–SiC structures by various methods are presented. The structures represent a highly doped n+ substrate with epitaxial layers 5...     

Optical and mechanical properties of C,Si, Ge,and 3C–SiC determined by first-principles theory using Heyd–Scuseria–Ernzerhof functional

Accurately calculating the band gap and electronic state density distribution of crystals is significant in determining optical properties. First-principles calculations were based on the projector-augmented-wave method with the Perdew–Burke–Ernzerhof generalized gradient approximation functional, pure density functional theory (DFT) and Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Such calculations account for the lattice parameters, electronic structure, optical properties, and mechanical properties of materials, which include the diamond-C and zinc blende structure of Si, Ge, and 3C–SiC in this study. The results obtained with HSE calculations is more accurate than that of the pure DFT calculations, and consistent with previous experimental values. The band structure and density of states of Si, Ge, and 3C–SiC indicate that these materials are indirect band gap materials. Based on HSE calculation, the band gap of Si and 3C–SiC is in accordance with previous experimental values. The imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient also matches previous experimental values. A corresponding relationship exists among the peak of the imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient. The optical properties have a direct relationship with the distribution of the crystal band gap and electronic state density. The materials exhibit brittleness. Although 3C–SiC is not as hard and stiff as diamond, it is a better semiconductor than Si and Ge. The mechanical anisotropy of the four materials is inconspicuous. The anisotropy of diamond-C in terms of its Young's modulus is extremely inconspicuous.     

C2H4,NH3及C3H6的脉冲激光光声谱

本文用光声法检测了9.2～10.8μm波长范围内C_2H_4、NH_3及C_3H_6分子对CO_2激光的吸收特性,获得了这三种气体分子的单脉冲激光光声光谱,测量了光声信号随实验参量(样品气压、激光能量)的变化关系,用光声法获得了样品气体中的声速及各种气体分子的V-T驰豫时间。     

4H–SiC BJTs with current gain of 110

4H–SiC BJTs with a common emitter current gain of 110 have been demonstrated. The high current gain was attributed to a thin base of 0.25 μm which reduces the carrier recombination in the base region. The device open base breakdown voltage (BV_CEO) of 270 V was much less than the open emitter breakdown voltage (BV_CBO) of 1560 V due to the emitter leakage current multiplication from the high current gain by “transistor action” of BJTs. The device has shown minimal gain degradation after electrical stress at high current density of >200 A/cm²up to 25 h.     

电力器件用的6H—SiC,3C—SiC和Si的比较

为了实现５０～５００Ｖ的击穿电压范围，本文详细讨论了６Ｈ－ＳｉＣ和３Ｃ－ＳｉＣ肖特基整流器和功率ＭＯＳＦＥＴ的漂移区性质。利用这些数据计算了器件的输出特性，并与Ｓｉ器件做了比较，结果表明，由于其漂移区电阻非常低，故５０００ＶＳｉＣ肖特基整流器和功率ＭＯＳＦＥＴ在室温下能够处理１００Ａ／ｃｍ＾２的导通电流密度，正向压降仅分别为３．８５和２．９５Ｖ。这些数值甚至优于Ｓｉｐｉｎ整流器和门可关断晶闸管。这     

Preparation,Structure and DC Conductivity of Organic Semiconductor PANI—C4H6O6

A new organic semiconductor tartaric acid doped salt of emeraldine polyaniline(PANI-C4H6O6)has been obtained by the method of oxidative polymerization of monomeric aniline with ammonium persulfate in acidic solution.The structure was characterized by Fourier Transform Infrared technique(FTIR) and X-ray diffraction(XRD).The temperature dependence dc conductivity δdc(T)shows a semiconductor behavior and follows the quasi one dimensional variable range hopping(Q1D-VRH)model.Data on δdc(T) are also discussed.     

Advanced SPICE-Modeling of 4H-SiC MESFETs

A modified drain source current suitable for simulation program with integrated circuit emphasis （SPICE） simulations of SiC MESFETS is presented in this paper. Accurate modeling of SiC MESFET is achieved by introducing three parameters in Triquint＇s own model （TOM）. The model, which is single piece and continuously differentiable, is verified by measured direct current （DC） I-V curves and scattering parameters （up to 20 GHz）.     

Numerical Analysis of Gate-to-Source Distance Effects in SiC MESFETs

Two-dimensional DC and small-signal analysis of gate-to-source scaling effects in SiC-based high-power field-effect transistors have been performed in this paper. The simulation results show that a downscaling of gate-to-source distance can improve device performance, i.e. enhancing drain current, transconductance, and maximum oscillation frequency. This is associated with the peculiar dynamic of electrons in SiC MESFETs, which lead to a linear velocity regime in the source access region. The variations of gate-to-source capacitance, gate-to-drain capacitance, and cut-off frequency with respect to the change in gate-to-source length have also been studied in detail.     

Photoluminescence Evaluation of p and n Type 6H—SiC

Photoluminescence evaluation of p and n type 6H-SiC samples has been done.Results show that at low temperature the photoluminescence of 6H-SiC is clearly dominated by donor-acceptor pair transitions,in some case,free-to-donor transition could be observed at higher temperature.The thermal quenching processes of the photoluminescence have been investigated to determine the possible ionization nenergies of the impurities.     

High temperature Hall effect measurements of semi-insulating 4H–SiC substrates

High temperature Hall effect and resistivity measurements have been made on semi-insulating 4H–SiC samples. Both vanadium doped and undoped materials have been studied. Resistivity measurements before and after annealing up to 1800 °C are also reported. The thermal activation energy of the resistivity in vanadium doped samples has one of two values, 1.5 and 1.1 eV, due, respectively, to the vanadium donor level and an as yet unidentified defect. The activation energies for high purity semi-insulating material (HPSI) varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI and 1.1 eV V-doped samples. In all cases the material was found to be n-type. Mixed conduction analysis of the data suggests that the hole concentration is negligible in all samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap. The resistivity of V-doped samples were unaffected by anneals up to 1800 °C. The annealing results for HPSI samples were mixed.     

Phosphorous passivation of the SiO2/4H–SiC interface

We describe experimental and theoretical studies to determine the effects of phosphorous as a passivating agent for the SiO₂/4H–SiC interface. Annealing in a P₂O₅ ambient converts the SiO₂ layer to PSG (phosphosilicate glass) which is known to be a polar material. Higher mobility (approximately twice the value of 30–40 cm²/V s obtained using nitrogen introduced with an anneal in nitric oxide) and lower threshold voltage are compatible with a lower interface defect density. Trap density, current–voltage and bias-temperature stress (BTS) measurements for MOS capacitors are also discussed. The BTS measurements point to the possibility of an unstable MOSFET threshold voltage caused by PSG polarization charge at the O–S interface. Theoretical considerations suggest that threefold carbon atoms at the interface can be passivated by phosphorous which leads to a lower interface trap density and a higher effective mobility for electrons in the channel. The roles of phosphorous in the passivation of correlated carbon dangling bonds, for SiC counter-doping, for interface band-tail state suppression, for Na-like impurity band formation and for substrate trap passivation are also discussed briefly.     

半绝缘3英寸6H SiC衬底

据《CompoundSemiconductor》2006年第4期报道,欧洲领先的SiC供应商德国SiCrystal公司,最近开始量产3英寸半绝缘衬底,这是它迈向功率器件、射频和光电应用领域的又一个里程碑。据悉,这次产品在质量方面作了重大的改进:低应力、微管少且具有很好的同质电阻率。这次siC晶圆表现出的固有物理特性,有利于器件制造商生产具有更多功能时实现体积更小,重量更轻,且可行性更强。据SiCrystal公司表示:它将适用于不同产品规格的客户,加速了下一代宽禁带器件的商业化,让SiC电子产品更快地推广市场。半绝缘3英寸6H SiC衬底@孙再吉…     

电力器件用的6H－SiC、3C－SiC和Si的比较

为了实现５０～５００Ｖ的击穿电压范围，本文详细讨论了６Ｈ－ＳｉＣ和３Ｃ－ＳｉＣ肖特基整流器和功率ＭＯＳＦＥＴ的漂移区性质。利用这些数值计算了器件的输出特性，并与Ｓｉ器件做了比较，结果表明，由于其漂移区电阻非常低，故５０００ＶＳｉＣ肖特基整流器和功率ＭＯＳＦＥＴ在室温下能够处理１００Ａｌｃｍ￣２的导通电流密度，正向压降仅分别为３．８５和２．９５Ｖ。这些数值甚至优于Ｓｉｐｉｎ整流器和门可关断晶闸管。这种ＳｉＣ器件由于没有少于结，故可期望有优良的开关特性和坚固耐用性。此外，还基于峰值结温极限是由封装考虑来确定的观点，报道了热学分析结果。应用这种分析发现，５０００Ｖ的６Ｈ－ＳｉＣ和３Ｃ－ＳｉＣＭＯＳＦＥＴ和肖特基整流器将比相应的Ｓｉ器件大约小２０和１８倍。对ＳｉＣ的热学分析表明，这些器件能在比常规Ｓｉ器件高的温度和击穿电压下工作。还有，在管芯尺寸上也期望有明显的减少，这将会补偿其材料成本较高的不足。本文报告的分析结果对ＳｉＣ功率器件的制造将会起到强大的推动作用。     

Microstructure and electrical properties of nitrogen doped 3C–SiC thin films deposited using methyltrichlorosilane

The growth, microstructure and electrical properties of in-situ nitrogen doped 3C–SiC (111) thin films for sensor applications are presented in this paper. These thin films are deposited at a pressure of 2.5 mbar and temperature of 1040 °C on thermally oxidized Si (100) substrates from methyltrichlorosilane (MTS) precursor using a hot wall vertical low pressure chemical vapor deposition (LPCVD) reactor. Ammonia (NH₃) is used as the nitrogen doping gas. The sensor response depends on chemical composition, structure, morphology and operating temperature. The above properties are investigated for all in situ nitrogen doped (0, 9, 17 and 30 at% of nitrogen) 3C–SiC thin films using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and four probe method. The XRD patterns of the 3C–SiC thin films show a decrease in the crystallinity and intensity of the peak with increase in dopant concentration from 0 to 17 at%. AFM investigations show an improvement in the grain size of the nitrogen doped 3C–SiC thin films with increase in nitrogen concentration from 0 to 17 at%. The sheet resistance of nitrogen doped 3C–SiC thin films is measured by the four probe technique and it is found to decrease with increase in temperature in the range of 40–550 °C. The resistivity and average temperature coefficient of resistance (TCR) of doped 3C–SiC thin film deposited with 17 at% of nitrogen concentration are found to be 0.14 Ω cm and −103 ppm/°C, respectively and this can be used as a sensing material for high temperature applications.     

Influence of inhomogeneous contact in electrical properties of 4H–SiC based Schottky diode

Schottky diodes realized on 4H–SiC n-type wafers with an epitaxial layer and a metal-oxide overlap for electric field termination were studied. The oxide was grown by plasma enhanced chemical vapor deposition (PECVD) and the Schottky barriers were formed by thermal evaporation of titanium or nickel. Diodes, with voltage breakdown as high as 700 V and ideality factor as low as 1.05, were obtained and characterized after packaging in standard commercial package (TO220).The electrical properties such as ideality factor, hight barrier, the series resistance R_s were deduced by current/voltage (I–V) analysis using the least mean square (LMS) method. The temperature effect on break voltage, R_s and saturation current was studied. A model based on two parallel Schottky diodes with two barrier heights is presented for some devices having an inhomogeneous contact. It is shown that the excess current at low voltage can be explained by a lowering of the Schottky barrier in localized regions. We use the two series RC components electrical model in order to study the dynamic behaviour of the Schottky diode in low frequency and to improve the effect of barrier inhomogeneities in electrical properties.     

硅熔体中3C—SiC的生长及6H—SiC晶型的抑制

论述了从硅熔体中生长3C－SiC晶体过程中6H－SiC晶型控制的一般原理,采用将硅置于高纯石墨坩埚中使其在高温条件下熔化。坩埚内壁石墨自然熔解于硅熔体中形成碳饱和的硅熔体,在石墨表面形成厚约0．2mm的SiC薄层。X射线衍射（XRD）、X射线光电子能谱（XPS）、Raman散射等分析表面所制备样品为3C－SiC多晶体,实验结果进一步证明从硅熔体中生长3C－SiC晶体过程中,通过适当调整工艺参数可以抑制6H－SiC晶型的形成。     

Carrier lifetime investigation in 4H–SiC grown by CVD and sublimation epitaxy

Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 μs may be observed in the mid-region of 40 μm thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the ‘true’ lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.     

Gain improvement and microwave operation of 4H–SiC MESFET with a new recessed metal ring structure

A new multi-recessed 4H-SiC MESFET with recessed metal ring for RF embedded circuits is proposed (MR2-MESFET). The key idea in the proposed structure is based on the elimination of the spaces adjacent to gate and stopped the depletion region extending towards drain and source and the reduction of the channel thickness between gate and drain to increase breakdown voltage (V_BR); meanwhile the elimination of the gate depletion layer extension to source/drain to decrease gate-source capacitance (C_gs). The influence of multi-recessed drift region and recessed metal ring structures on the characteristics of the MR2-MESFET is studied by numerical simulation. The optimized results show that the V_BR of the MR2-MESFET is 119% larger than that of the conventional 4H–SiC MESFET (C-MESFET); meanwhile maintain 85% higher saturation drain current. Therefore, the maximum output power density of the MR2-MESFET is 23.1 W/mm compared to 5.5 W/mm of the C-MESFET. Also, the cut-off frequency (f_T) and the maximum oscillation frequency (f_max) of 24.9 and 91.7 GHz are obtained for the MR2-MESFET compared to 11 and 40 GHz of the C-MESFET structure, respectively. The proposed MR2-MESFET shows a maximum stable gain (MSG) exceeding 23.6 dB at 3.1 GHz which is the highest gain yet reported for SiC MESFETs, showing the potential of this device for high power RF applications.     

Comparison of GexSi1—x Grown by UHV／CVD from Si2H6／GeH4 and SiH4／GeH4

Using double crystal X-rays diffraction (DCXRD) and atomic force microscopy (AFM), the results of Ge x Si 1- x grown by UHV/CVD from Si 2H 6 and SiH 4 are analyzed and compared. Adsorbates can migrate to the energy-favoring position due to the slow growth rate from SiH 4. In this case, a Si buffer that isolates the effect of substrate on epilayer could not be grown, which results in a pit penetrating into epilayer and buffer. The FWHM is 0.055° in DCXRD from SiH 4. The presence of diffraction fringes is an indication of an excellent crystalline quality. The roughness of the surface is improved if grown by Si 2H 6; however, the crystal quality of the Ge x Si 1- x material became worse than that from SiH 4 due to much larger growth rate from Si 2H 6. The content of Ge is obtained from DCXRD, which indicates the growth rate from Si 2H 6 is largest, then GeH 4, and that from SiH 4 is least.