Comparative study on transport properties of N-, P-, and As-doped SiC nanowires: Calculated based on first principles

According to the one-dimensional quantum state distribution, carrier scattering, and fixed range hopping model, the structural stability and electron transport properties of N-, P-, and As-doped SiC nanowires(N-SiCNWs, P-SiCNWs, and As-SiCNWs) are simulated by using the first principles calculations. The results show that the lattice structure of NSiCNWs is the most stable in the lattice structures of the above three kinds of doped SiCNWs. At room temperature,for unpassivated SiCNWs, the doping effect of P and As are better than that of N. After passivation, the conductivities of all doped SiCNWs increase by approximately two orders of magnitude. The N-SiCNW has the lowest conductivity. In addition, the N-, P-, As-doped SiCNWs before and after passivation have the same conductivity–temperature characteristics,that is, above room temperature, the conductivity values of the doped SiCNWs all increase with temperature increasing.These results contribute to the electronic application of nanodevices.     

Formation of the intermediate semiconductor larger for the Ohmic contact to silicon carbide using Germanium implantation

By formation of an intermediate semiconductor layer (ISL) with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method (TLM) test patterns is formed on N-wells created by P⁺ ion implantation into Si-faced p-type 4H-SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance ρ_c as low as 4.23× 10^-5~Ωega \cdotcm² is achieved after annealing in N₂ at 800~°C for 3~min, which is much lower than that (>900~°C) in the typical SiC metallisation process. The sheet resistance R_sh of the implanted layers is 1.5~kΩega /\Box. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge⁺ ion implantations.     

Influence of silicon and carbon excesses on the aqueous dispersion of SiC nanocrystals for optical application

The dispersion behaviour of laser-synthesized silicon carbide nanoparticles (npSiC) in water is investigated by photon correlation spectroscopy (PCS). With regard to previous studies and due to an application in the processing of optical materials, this paper concerns low npSiC contents (from 0.05 to 10 wt.%). The role played by the particle surface state is be pointed out through the consideration of stochiometric (C/Si = 1), carbon-rich (C/Si > 1) and silicon-rich (C/Si < 1) nanopowders. Suspensions made from stoichiometric and silicon-rich nanopowders are easily dispersed and stable with time. The PCS measurements reveal in this case more than 95% of isolated nanoparticles, pointing out the key role of the oxidized layer covering the grain of silicon-rich samples. At the opposite, the carbon-rich powders are hardly dispersed in pure water, correlated with the presence of a relatively inert graphitic carbon layer at the grain surface. However, by addition of a commercial polymeric dispersant, all nanopowders induce high quality suspensions. In particular, the carbon-rich samples are easily dispersed, and possible dispersion mechanisms of npSiC in presence of a polymeric surfactant are discussed. The influence of the npSiC loading and the time evolution of the suspension are also presented. By considering stoichiometric, as well as carbon- and silicon-rich samples, this paper demonstrates the possibility to achieve high quality dispersions of SiC nanoparticles, whatever the chemical composition of the powder, as an easy step for optical material processing.This revised version was published online in August 2005 with a corrected issue number.     

Preparation and characterizations of amorphous nanostructured SiC thin films by low energy pulsed laser deposition

Amorphous silicon carbide (SiC) thin films were deposited on silicon substrates by pulsed laser ablation at room temperature. Thicknesses and surface morphology of the thin films were characterized using optical profilers, atomic force and field emission scanning electron microscopy. Nanohardnes, modulus and scratch resistance properties were determined using XP nanoindenter. The results show that crack free, smooth and nanostructured thin films can be deposited using low laser energy densities.     

Delaminated zeolite‐catalysed synthesis of high‐molecular weight polycarbosilane as a low shrinkage SiC precursor

A polycarbosilane (PCS) with a higher number–average molecular weight (2710 vs. 1570), and hence with a higher ceramic yield (74 vs. 68%), compared to a commercial Nipusi type S PCS has been synthesized via the catalytic decomposition of polydimethylsilane at 400 °C using H‐ITQ‐2, a delaminated zeolite with a very high external surface area, as a solid acid. The silicon carbide film fabricated using this PCS was found to show a much lower level (16 vs. 39%) of shrinkage than the commercial PCS‐derived film, together with better mechanical properties, suggesting the potential of its preceramic polymer to produce robust ceramic coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 725–732, 2008     

纳米SiC蓝光发射的研究

在４．６８ｅＶ的激光激发下，室温ＣＶＤ合成的纳米ＳｉＣ粉体，可发射４７５ｎｍ的蓝光，经６００～１１００℃在Ｎ２气氛下进行快速退火（ＲＴＡ）处理，其荧光强度随退火温度升高而增强，当Ｔ≥９００℃时，荧光强度下降，但发光峰位与退火温度无关．通过ＸＲＤ、ＩＲ、ＴＥＭ、ＸＰＳ等研究，认为纳米ＳｉＣ中与氧有关的缺陷可能是引起４７５ｎｍ蓝光发射的主要原因     

Impact of O_2 post oxidation annealing on the reliability of SiC/SiO_2 MOS capacitors

The effects of dry O_2 post oxidation annealing(POA) at different temperatures on SiC/SiO_2 stacks are comparatively studied in this paper. The results show interface trap density(Dit) of SiC/SiO_2 stacks, leakage current density(Jg), and time-dependent dielectric breakdown(TDDB) characteristics of the oxide, are affected by POA temperature and are closely correlated. Specifically, Dit, Jg, and inverse median lifetime of TDDB have the same trend against POA temperature, which is instructive for SiC/SiO_2 interface quality improvement. Moreover, area dependence of TDDB characteristics for gate oxide on SiC shows different electrode areas lead to same slope of TDDB Weibull curves.     

Optical spectroscopy study of damage evolution in 6H-SiC by H_2~+ implantation

Lattice defects induced by ion implantation into Si C have been widely investigated in the decades by various techniques. One of the non-destructive techniques suitable to study the lattice defects in Si C is the optical characterization. In this work, confocal Raman scattering spectroscopy and photoluminescence spectrum have been used to study the effects of 134-ke V H_2~+ implantation and thermal treatment in the microstructure of 6 H-Si C single crystal. The radiation-induced changes in the microstructure were assessed by integrating Raman-scattering peaks intensity and considering the asymmetry of Raman-scattering peaks. The integrated intensities of Raman scattering spectroscopy and photoluminescence spectrum decrease with increasing the fluence. The recovery of the optical intensities depends on the combination of the implantation temperature and the annealing temperature with the thermal treatment from 700℃ to 1100℃. The different characterizations of Raman scattering spectroscopy and photoluminescence spectrum are compared and discussed in this study.     

Eight MeV per charge state from 300 ps laser ion acceleration by using micrometric foils

Proton acceleration using high-intensity laser pulses, at 10¹⁶ W/cm² was studied irradiating different types of thin metal and plastic targets having 1-micron thickness. The maximization of the proton energy process was investigated optimizing the laser parameters, the irradiation conditions and the target properties. Employing 600–700 J laser pulse energy, a focalization inducing self-focusing effects and using targets with optimized thickness, it was possible to accelerate protons up to energies of above 8 MeV. The time-of-flight diagnostics has allowed to monitor the plasma properties and to control the ion acceleration process.     

面向单晶SiC原子级表面制造的等离子体辅助抛光技术

目前Si基半导体由于其自身材料特性的限制,已经越来越难以满足高速发展的现代电力电子技术对半导体器件的性能要求.SiC作为新一代半导体材料具有显著的性能优势,但由于其属于典型的难加工材料,实现SiC晶圆的高质量与高效率加工成为了推动其产业化应用进程的关键.本综述在回顾近年来SiC超精密加工技术研究进展的基础上,重点介绍了一种基于等离子体氧化改性的SiC高效超精密抛光技术,分析了该技术的材料去除机理、典型装置、改性过程及抛光效果.分析结果表明,该技术具有较高的去除效率,能够获得原子级平坦表面,并且不会产生亚表面损伤.同时针对表面改性辅助抛光技术加工SiC表面过程中出现的台阶现象,探讨了该台阶结构的产生机理及调控策略.最后对等离子体辅助抛光技术的发展与挑战进行了展望.