Electron paramagnetic resonance characterization of aluminum ion implantation-induced defects in 4H-SiC

Deep-level defects in silicon carbide(SiC) are critical to the control of the performance of SiC electron devices. In this paper, deep-level defects in aluminum ion-implanted 4 H-SiC after high-temperature annealing were studied using electron paramagnetic resonance(EPR) spectroscopy at temperatures of 77 K and 123 K under different illumination conditions. Results showed that the main defect in aluminum ion-implanted 4 H-SiC was the positively charged carbon vacancy( VC~+), and the higher the doping concentration was, the higher was the concentration of VC~+. It was found that the type of material defect was independent of the doping concentration,although more VC~+ defects were detected during photoexcitation and at lower temperatures. These results should be helpful in the fundamental research of p-type 4 H-SiC fabrication in accordance with functional device development.     

Electrical and optical properties of p-SiC/n-GaN heterostructures

We report on the optical, electrical and structural properties of GaN films heteroepitaxially grown by low pressure chemical vapor deposition on 6H-SiC substrates. We employed photoluminescence (PL), Hall effect measurements, scanning tunneling microscopy (STM) and X-ray analysis to determine the quality of our films. Heterojunction diodes were fabricated on p-type SiC and characterized by temperature dependent current–voltage and capacitance–voltage techniques. The results are interpreted within the thermionic emission model and the barrier found is attributed to the conduction band offset between 6H-SiC and wurtzite GaN. The diodes show electroluminescence of the donor-acceptor pair recombination type of 6H-SiC at room temperature. By analysis of the injection behavior we can interpret our data, determining the high valence band offset between 6H-SiC and -GaN to 0.67 eV. This high valence band offset favors applications for hetero-bipolar transistors (HBT).     

Silicon carbide and diamond for high temperature device applications

The physical and chemical properties of wide bandgap semiconductors silicon carbide and diamond make these materials an ideal choice for device fabrication for applications in many different areas, e.g. light emitters, high temperature and high power electronics, high power microwave devices, micro-electromechanical system (MEMS) technology, and substrates. These semiconductors have been recognized for several decades as being suitable for these applications, but until recently the low material quality has not allowed the fabrication of high quality devices. Silicon carbide and diamond based electronics are at different stages of their development. An overview of the status of silicon carbide's and diamond's application for high temperature electronics is presented. Silicon carbide electronics is advancing from the research stage to commercial production. The most suitable and established SiC polytype for high temperature power electronics is the hexagonal 4H polytype. The main advantages related to material properties are: its wide bandgap, high electric field strength and high thermal conductivity. Almost all different types of electronic devices have been successfully fabricated and characterized. The most promising devices for high temperature applications are pn-diodes, junction field effect transistors and thyristors. MOSFET is another important candidate, but is still under development due to some hidden problems causing low channel mobility. For microwave applications, 4H-SiC is competing with Si and GaAs for frequency below 10 GHz and for systems requiring cooling like power amplifiers. The unavailability of high quality defect and dislocation free SiC substrates has been slowing down the pace of transition from research and development to production of SiC devices, but recently new method for growth of ultrahigh quality SiC, which could promote the development of high power devices, was reported. Diamond is the superior material for high power and high temperature electronics. Fabrication of diamond electronic devices has reached important results, but high temperature data are still scarce. PN-junctions have been formed and investigated up to 400 ^∘C. Schottky diodes operating up to 1000 ^∘C have been fabricated. BJTs have been fabricated functioning in the dc mode up to 200 ^∘C. The largest advance, concerning development of devices for RF application, has been done in fabrication of different types of FETs. For FETs with gate length 0.2 μ m frequencies f_T = 24.6 GHz, f_{max (MAG)} = 63 GHz and f_{max (U)} = 80 GHz were reported. Further, capacitors and switches, working up to 450 ^∘C and 650 ^∘C, respectively, have also been fabricated. Low resistant thermostable resistors have been investigated up to 800 ^∘C. Temperature dependence of field emission from diamond films has been measured up to 950 ^∘C. However, the diamond based electronics is still regarded to be in its infancy. The prerequisite for a successful application of diamond for the fabrication of electronic devices is availability of wafer diamond, i.e. large area, high quality, inexpensive, diamond single crystal substrates. A step forward in this direction has been made recently. Diamond films grown on multilayer substrate Ir/YSZ/Si(001) having qualities close those of homoepitaxial diamond have been reported recently.     

Preparation of silicon carbide using bamboo charcoal as carbon source

Silicon carbide (SiC) was prepared by carbothermal reduction with amorphous silica sol as silicon source and bamboo charcoal powder as carbon source. The compositions and microstructure of prepared SiC were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). XRD of prepared SiC showed that the major phase of prepared SiC was hexagonal 6H-SiC with the existence of some 4H-SiC. SEM showed that SiC particle was granular, rod-like and of tower-shape, and it inherited the shape of bamboo charcoal. EDS showed that prepared SiC was pure without being doped by the mineral elements from bamboo charcoal.     

Single crystal diamond M?i?P diodes for power electronics

Its outstanding electronic properties and the recent advances in growing single-crystal chemically vapour-deposited substrates have made diamond a candidate for high-power applications. Diamond Schottky diodes have the potential of being an alternative to silicon p-i-n and SiC Schottky diodes in power electronic circuits. Extensive experimental and theoretical results, for both on- and off-state behaviour of metal-insulator-p-type diamond Schottky structures, are presented here. The temperature dependence of the forward characteristics and electrical performance of a termination structure suitable for unipolar diamond devices are also presented.     

Concepts for diamond electronics

The present status in the development of diamond as electronic semiconductor material with wide band-gap (5.45 eV) is reviewed. Since diamond cannot be doped with shallow impurities, specific doping concepts and related diode and FET structures had to be developed, restricted to p-type boron doping. The results allow to predict that diamond high voltage switching diodes, high power RF FET sources and operation at high temperature will surpass the capability of devices designed in competing wide band-gap materials like SiC and GaN.     

Screening of metal flux for SiC solution growth by a thin-film combinatorial method

4H-SiC is a wide-bandgap semiconductor with potential applications in power devices. The lack of a liquid phase in SiC hinders conventional crystal growth from the melt; consequently, SiC wafers still have low quality and are nearly 100 times more expensive than Si wafers. To take advantage of the solution growth for improving the quality and reducing the cost of SiC, Ni addition to Si–Ti flux has been investigated. A combinatorial approach was employed to accelerate the screening of metal flux for the SiC solution growth.     

硅基沉积氮化镓,碳化硅,III –V 族及其合金材料研究进展

硅基沉积氮化镓, 碳化硅, III-V 族及其合金材料是近年来的研究热点. 氮化镓, 碳化硅及其III-V 材料在光电子和电子元件领域有着广泛的应用.例如大功率, 高速器件, 大型激光器, 紫外探测器等等. 尽管硅基片具有低成本, 大的尺寸,和极好的电热导性能等优点, 硅基片仍没有成为氮化镓, 碳化硅及III – V 的主要沉积基片, 其原因在于硅基片与氮化镓, 碳化硅及III-V 材料之间的热膨胀系数和晶格常数之间的失配. 自从1998年, IBM 的课题组用分子外延方法在硅基片上沉积氮化镓, 并且成功地制备了氮化镓激光器之后, 硅基氮化镓的研究开始备受关注. 近年来的研究发现, 使用氧化铝和氮化铝镓作为过渡层. 硅基氮化镓的热应力及与硅基片之间的晶格失配可以明显降低.在 6英寸的(111) 取向的硅基片上用化学气相方法可以成功地沉积超过一个微米厚的无裂纹的单晶氮化镓. 德国的AZZURRO 公司成功地制备硅基片氮化镓的大功率的蓝色激光器. 美国的NITRINEX公司也生产了硅基氮化镓大功率电子元件. 超大功率的硅基氮化镓电子元件仍在研究中. 在2007年, 英国政府设立了一个固体照明器件的研究项目. 主要着手研究6英寸的硅基氮化镓激光器. 另一方面, 在过去的40年, 超大规模硅基CMOS 技术已有了长足的发展, 下一代低功耗高速逻辑电路要求低的驱动电流, 小的活门尺寸低于 30 nm 和快速反应性能. 这就要求器件通道材料具有很高的电子(或空穴)迁移率. III-V 材料, 例如InSb, InAs, 和InGaAs 具有电子迁移率高达 80000 cm2/VS. 它们将是下一代低于 30 nm 硅基CMOS 器件最好的候选材料. 在 2007 年美国DARPA/MTO 设立了一个研究项目来发展硅基 III-V材料器件, 着重于发展高速硅基III-V材料CMOS 器件. 第一届”硅基氮化镓,碳化硅,III-V及其合金材料研究进展 ”国际会议也将于3月 24日-28日在旧金山MRS 2008年初春季会议上召开.     

Three-dimensional observation of defects in nitrogen-doped 6H-SiC crystals using a laser scanning confocal microscope

Different defective structures of nitrogen-doped 6H-SiC single crystals were examined using a combination of laser scanning confocal microscopy (LSCM), scanning electron microscope (SEM) and KOH–K₂CO₃ etching. The form, depth and size of the defects in etched silicon carbide (SiC) crystals were observed by LSCM. Using these 3D LSCM images, defective structures varying in the growth direction were observed from a side view for the first time. To study the size, depth and form of defect etch pits in detail, we observed the defect etch pits configuration in some volumes through taking 3D LSCM pictures. Information on defects obtained using this approach will be very helpful for investigation of MP and SD formation mechanism in conducting SiC substrates, as well as the observation of polytype stability in nitrogen-doped SiC crystals.     

Screening of metal flux for SiC solution growth by a thin-film combinatorial method

Abstract

4H-SiC is a wide-bandgap semiconductor with potential applications in power devices. The lack of a liquid phase in SiC hinders conventional crystal growth from the melt; consequently, SiC wafers still have low quality and are nearly 100 times more expensive than Si wafers. To take advantage of the solution growth for improving the quality and reducing the cost of SiC, Ni addition to Si–Ti flux has been investigated. A combinatorial approach was employed to accelerate the screening of metal flux for the SiC solution growth.     

Heteropolytype structures with SiC quantum dots

Epitaxial silicon carbide layers of 3C-SiC polytype with an array of nanodimensional SiC quantum dots (QDs) have been obtained for the first time using an improved method of sublimation epitaxy in vacuum. The X-ray topography and X-ray diffraction data unambiguously confirm the formation of a 3C-SiC epilayer with twinned regions on the surface of a 6H-SiC substrate. The surface topography of epilayers was studied by atomic force microscopy (AFM), and the microstructure of a near-surface layer of the deposit was investigated by transmission electron microscopy (TEM). Using the AFM and TEM data, the presence of QDs (representing SiC nanoislands) is established, and their average dimensions and concentration are evaluated.     

Homoepitaxial 6H-SiC thin films by vapor-liquid-solid mechanism

Silicon carbide (SiC) is a IV-IV compound semiconductor with a wide energy band gap. Because of its outstanding properties, SiC can be used in high-power, high-temperature devices with high radiation resistance. In this study, a two-step vapor-liquid-solid (VLS) method was proposed for homoepitaxial growth of high quality 6H-SiC thin films, combining VLS growth and conventional chemical vapor deposition (CVD) processes. VLS growth was used to eliminate the micro-pipes (MPs) in the first step, and the subsequent step based on the CVD process was employed to improve the surface roughness. The morphology and structure of the as-grown thin films were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, atomic force microscopy and high-resolution X-ray diffraction, showing that thin films grown by two-step method have good crystalline quality and small surface roughness.     

Surface nano-structured silicon carbide thin film produced using hot filament decomposition of ethylene at low temperature on silicon wafer

The structure and spectroscopic properties of nano-structured silicon carbide (SiC) thin films were studied for films obtained through deposition of decomposed ethylene (C₂H₄) on silicon wafers via hot filament chemical vapor deposition method at low temperature followed by annealing at various temperatures in the range 300-700 °C. The prepared films were analyzed with focus on the early deposition stage and the initial growth layers. The analysis of the film's physics and structural characteristics was performed with Fourier transform infrared spectroscopy and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. The conditions for forming thin layer of cubic SiC phase (3C-SiC) are found. X-ray diffraction and Raman spectroscopy confirmed the presence of 3C-SiC phase in the sample. The formation conditions and structure of intermediate SiC layer, which reduces the crystal lattice mismatch between Si and diamond, are essential for the alignment of diamond growth. This finding provides an easy way of forming SiC intermediate layer using the Si from the substrate.     

Interfacial transformations in the a-SiC/a-Si/6H-SiC structure caused by high-temperature (1500°C) annealing

We have studied the reactions that take place at interfaces in an a-SiC/a-Si/6H-SiC sandwich structure, which was obtained by the sequential deposition of amorphous silicon (a-Si) and amorphous silicon carbide (a-SiC) onto a 6H-SiC substrate by ion sputtering in vacuum and then annealed at 1500°C (i.e., above the melting point of silicon). It is shown that the annealing leads to complete îdissipationî of the silicon film in SiC, probably as a result of the dissolution of carbon in the silicon melt and the diffusion of silicon into SiC.     

掺氮碳化硅晶体的近红外光谱研究

分别用红外光谱测量系统和双光束分光光度计研究了室温下碳化硅单晶的光学性质,测得碳化硅晶体的透射率和反射率随波变化的关系.通过掺氮与非掺杂碳化硅各种光谱的比较,发现掺氮不仅使近红外透射率降低,也导致反射率下降,掺氮碳化硅晶体在可见光部分出现了比较明显的吸收带.此外,利用透射谱还获得非掺杂6H-SiC晶体的折射率.     

金刚石/碳化硅复合梯度膜制备研究

采用微波等离子化学气相沉积(MW-PCVD)制备金刚石/碳化硅复合梯度膜.工作气体为H₂,CH₄和Si[CH₃]₄(四甲基硅烷,TMS),其中H₂∶CH₄=100∶0.6,Si[CH₃]₄为0％-O.05％,沉积压力为3300Pa,基体温度为700℃,微波功率为700W.基体为单晶硅,在沉积前用纳米金刚石颗粒处理.沉积后的样品经扫描电子显微镜(SEM),电子探针显微分析(EPMA),X射线能量损失分析(EDX)表明:沉积膜中的碳化硅含量是随Si[CH₃]₄流量的变化而改变.通过改变Si[CH₃]₄的流量可以制备金刚石/碳化硅复合梯度膜,且梯度膜中金刚石与复合膜过渡自然平滑.     

Mechanical and tribological behaviour of nano scaled silicon carbide reinforced aluminium composites

ABSTRACT

This work assesses the impact of the presence of Nano scaled silicon carbide on the Mechanical & Tribological behavior of aluminium matrix composites. Aluminium matrix composites containing 0, 0.5, 1, 1.5, 2 and 2.5 wt.%-nano scaled silicon carbide was set up by a mechanical stirrer. The trial comes about to demonstrate that the inclusion of Nano silicon carbide brings about materials with progressively high elastic modulus and likewise brings about expanded brittle behavior, fundamentally lessening failure strain. Shear modulus and flexural shear modulus likewise increases with silicon carbide increase. The presence of Nano scaled silicon carbide in the aluminium matrix diminishes subsurface fatigue wear and increases wear resistance, because of silicon carbide lubricant activity. Wear testing, microstructure & morphological, density & void testing, hardness, flexural and tensile test of the readied composites were investigated and outcomes were analyzed which demonstrated that including nano-SiC in aluminum (Al) matrix increased wear resistance, tensile strength, and 2 wt. % of nano scaled SiC for Al MMC indicated maximum wear resistance, tensile strength, and an optimum balanced mix of both Tribological and Mechanical properties. Microstructural observation uncovered uniformand homogeneous distribution of SiC particles in the Al matrix.     

颗粒整形对碳化硅陶瓷密封材料成型及烧结性能的影响

采用球磨对SiC粉体颗粒进行整形,并借助反应烧结制备SiC陶瓷密封材料,考察了颗粒整形对反应烧结SiC陶瓷成型、烧结性能、显微结构和力学性能的影响规律。结果表明,整形后的SiC颗粒的球形度高,粒径分布更为均匀;整形SiC粉体的振实密度和素坯密度明显提高,烧结体的显微结构更加均匀,主晶相为6H-SiC和Si,分布均匀,残炭很少;颗粒整形明显改善SiC陶瓷的成型性能及力学性能,当压力为15MPa时,整形后的SiC素坯密度为2.08g/cm~3,烧结体密度为3.06g/cm~3,抗弯强度和断裂韧性分别达到456MPa和3.87MPa·m1/2。     

Low-dimensional SiC nanostructures: Fabrication, luminescence, and electrical properties

Nanostructured silicon carbide has unique properties that make it useful in microelectronics, optoelectronics, and biomedical engineering. In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed. Silicon carbide nanocrystals are generally produced using two techniques, electrochemical etching of bulk materials to form porous SiC or embedding SiC crystallites in a matrix such as Si. Luminescence from SiC crystallites prepared by these two methods is generally believed to stem from surface or defect states. Stable colloidal 3C-SiC nanocrystals which exhibit intense visible photoluminescence arising from the quantum confinement effects have recently be produced. The field electron emission and photoluminescence characteristics of silicon carbide nanostructures as well as theoretical studies of the structural and electronic properties of the materials are described.     

Structural and optical properties of four-hexagonal polytype nanocrystalline silicon carbide films deposited by plasma enhanced chemical vapor deposition technique

Four-hexagonal polytype films of nanocrystalline silicon carbide (4H-nc-SiC) were deposited by plasma enhanced chemical vapor deposition method with more than 3×10⁴ W m⁻² threshold of power density, high hydrogen dilution ratio, and bias pretreatment. The source gases were silane, methane and hydrogen. Our work showed that under conditions similar to those used for the growth of μc-SiC—except a higher power densities over a threshold, a bigger bias pretreatment on substrates, and a moderate bias deposition—nc-SiC films could indeed be achieved. The Raman spectra and transmission electron microscopy diffraction patterns demonstrated that the as-grown films from the H₂-CH₄-SiH₄ plasma consist of amorphous network and phase-pure crystalline silicon carbide which has the 4H polytype structure. The microcolumnar 4H-SiC nanocrystallites of a mean size of approximately 1.6×10⁻⁸ m in diameter are encapsulated by amorphous SiC networks. The photoluminescence spectra of 4H-SiC at room temperature, peaking at 8.10×10⁻⁷ m using a wavelength of 5.145×10⁻⁷ m of argon ion laser, were obtained at room temperature; the luminescence mechanism is thought to be related to transitions in the energy band gap which could be ascribed to the surface states and defects in the structure of 4H-SiC nanocrystalline in these films due to its small size. The as-grown films showed an optical transmittance of 89% at 6.58×10⁻⁷ m. This higher transmittance is believed to be from the small size and amorphous matrix.