Analytical model of electron transport characteristics for 4H-SiC material and devices

Based on 4H-SiC material parameters, three different analytical expressions are used to characterize the electron mobility as the function of electric field. The first model is based on simple saturation of the steady-state drift velocity with electric field (conventional three-parameter model for silicon). The second GaAs-based mobility model partially reflects the peak velocity in high electric fields. The third multi-parameter model proposed in this paper is more realistic since it well reproduces the drift velocity－field characteristics obtained by Monte Carlo calculations, revealing the peak drift velocity with subsequent saturation at higher electric fields. Thus, the drift velocity model presented in this paper is much better for device simulation. In this paper, the influence of mobility model on DC characteristics of 4H-SiC MESFET is calculated and the better accordance with the experimental results is presented with multi-parameter model.     

PHOTOLUMINESCENCE OF NANOCRYSTALLINE SiC FILMS PREPARED BY RF MAGNETRON SPUTTERING

Amorphous SiC films are deposited on Si (111) substrates by rf magnetron sputtering and then annealed at 1200℃ for different times by a dc self-heating method in a vacuum annealing system. The crystallization of the amorphous SiC is determined by Raman scattering at room temperature and X-ray diffraction. The experimental result indicates that the SiC nanocrystals have formed in the films. The topography of the as-annealed films is characterized by atomic force microscopy. Measurements of photoluminescence of the as-annealed films show blue or violet light emission from the nanocrystalline SiC films and photoluminescence peak shifts to short wavelength side as the annealing time decreases.     

Fabrication and Luminescent Properties of 6H-SiC/3C-SiC/6H-SiC Quantum Well Structure

Quantum well structure film of 6H-SiC/3C-SiC/6H-SiC was fabricated on 6H-SiC (0001) with the substrate temperature of 1350 K by solid source molecular beam epitaxy (SSMBE) through the variation of Si flux rate. The crystal polytypes and luminescent properties of the film were characterized by reflection high energy electron diffraction (RHEED) and photoluminescence (PL), respectively. The results of RHEED indicated that the film was 6H-SiC/3C-SiC/6H-SiC with the quantum well structure. The results of PL excited by He-Gd laser at room temperature showed that there were intense emissions in the range of 480–600 nm, which could not be observed from the substrate. The fitting peaks were consistent with the results calculated from the model of quantum well structure, which showed that such intense emissions were probably from the quantum wells with different widths.     

Theoretical identification of the lowest-energy structure of (SiC)12 heterocluster: Segregation of C and Si in planar and cage structures

The structures and relative stabilities of various plane and cage isomers of (SiC)₁₂ cluster have been systematically computed using density functional theory at the level of BLYP. A number of starting configurations were generated from the low-energy isomers of C₂₄ cluster via replacing 12 C atoms by Si atoms, which are D_6h planar structure, and the D_6d, D_2h, O_h, and D_4h symmetrical fullerene cages. The heterofullerene cage obeying six isolated squares rules are not the most preferred structural motif for (SiC)₁₂ cluster. The structural candidates with fully alternating Si–C arrangement are energetically unfavorable. Instead, the (SiC)₁₂ cluster tend to adopt plane, bowl, saddle, and highly distorted cage structures. In all cases, segregation of C atoms is a common feature.     

Formation and Structure of Cluster-Included Carbon Nanocapsules Prepared by Polymer Pyrolysis

Abstract

Formation of carbon nanocapsules with various clusters (SiC, Au, Fe. Co. Ge. and GeO₂) by polymer pyrolysis was investigated, and nanocapsules with SiC and Au nanoparticles were produced by thermal decomposition of polyvinyl alcohol at ?500°C in Ar gas atmosphere. The formation mechanism of nanocapsules and a structural model for the nanocapsule/SiC interface were proposed. In addition, carbon clusters were formed at the surface of carbon nanocapsules, and carbon onions were produced by electron irradiation of amorphous carbon produced from polyvinyl alcohol. The present work indicates that the pyrolysis of polymer materials with clusters is a useful fabrication method for the mass-production of carbon nanocapsules and onions at low temperatures compared to the ordinaly are discharge method.     

Comparison of fibre/matrix interface strength for a 3D woven SiC/SiC composite

The fibre/matrix interface shear strength, τ _P, was determined by analysis of fibre pullout length distributions for a 3D woven SiC/SiC-based composite that had undergone tensile testing between room temperature and 1300°C in vacuum and air. Data was compared with the fibre/matrix interface shear strength, τ _S, obtained previously for this system by analysis of in situ fibre strength distributions. τ _P was found to follow the same general trend as that of τ _S and this was explained in terms of the carbon-rich fibre/matrix interface region. However, τ _P was smaller than τ _S by a factor of 3-4 for all cases, but the reason for this remains unclear although several tentative suggestions have been put forward.     

微米碳化硅晶须在水介质中的分散行为

以去离子水为分散介质,六偏磷酸钠(SHP)和羧甲基纤维素钠(CMC)为分散剂,利用沉降法、ζ电位、傅里叶变换红外光谱(FTIR)、TEM等测试技术研究了微米碳化硅晶须在水介质中的分散稳定机制,探讨了pH值、分散剂种类及含量对SiC微米晶须分散行为的影响机制。结果表明:微米SiC晶须的分散机理为静电稳定机制,pH值、SHP和CMC对微米SiC晶须的分散性和稳定性有较大影响;pH值为11时,微米SiC晶须的分散性和稳定性较好;SHP和CMC含量均为4wt%时,SiC微米晶须悬浮液具有良好的分散性能,分别在沉降时间18.5 h和22 h时相对沉降高度仍达96.89%和98%。六偏磷酸钠的分散机制主要以提高颗粒间的静电斥力为主,而羧甲基纤维素钠则为增大晶须表面的亲水性和提高晶须表面的电位绝对值。     

Extraction and scattering analyses of 2D and bulk carriers in epitaxial graphene-on-SiC structure

Hall effect measurements of a graphene-on-SiC system were carried out as a function of temperature (1.8–200 K) at a static magnetic field (0.5 T). With the analysis of temperature dependent single-field Hall data with the Simple Parallel Conduction Extraction Method (SPCEM), bulk and two-dimensional (2D) carrier densities and mobilities were extracted successfully. Bulk carrier is attributed to SiC substrate and 2D carrier is attributed to the graphene layer. For each SPCEM extracted carrier data, relevant three-dimensional or 2D scattering analyses were performed. Each SPCEM extracted carrier data were explained with the related scattering analyses. A temperature independent mobility component, which may related to an interaction between graphene and SiC, was observed for both scattering analyses with the same mobility limiting value. With the SPCEM, effective ionized impurity concentration of SiC substrate, extracted 2D-mobility, and sheet carrier density of the graphene layer are calculated with using temperature dependent static magnetic field Hall data.     

Fullerene-like Si60C60 nanocage: Hydrogen storage capacity

For investigating the hydrogen storage capacity of the Si₆₀C₆₀ nanocage, we have performed first principle density functional theory calculations with van der waals corrections. According to the force and energy minimization of the complex structures of nH₂@Si₆₀C₆₀, we have found that the systems with n = 1 to 70 are energetically favorable. We also found that the most stable nH₂@Si₆₀C₆₀ system is related to the systems with n close to 50 which make it possible to reach 4.2 wt% of hydrogen storage. Although it is found that the nH₂@Si₆₀C₆₀ system remains stable up to n = 70 and 5.8 wt%. The NPT molecular dynamic investigation at different pressures (0–30 atm) and also different temperatures (300–1800 K) were carried out on the optimized stable system with maximum capacity of encapsulating H₂ molecules (70H₂@Si₆₀C₆₀).     

CBr4 as precursor for VPE growth of cubic silicon carbide

This work presents a study of carbon tetrabromide (CBr₄) as precursor to deposit 3C‐SiC on (001) and (111) Si by VPE technique at temperatures ranging between 1000 °C and 1250 °C. TEM, AFM and SEM results indicate that the epitaxy proceeds as a 3D growth of uncoalesced islands at low temperature, whereas a continuous crystalline layer with hillocks on top is obtained above 1200 °C. The hillocks observed at high temperature appear well faceted and their shape and orientation are analyzed in detail by AFM, showing a {311} preferred orientation. 3D island growth was suppressed by adding C₃H₈ to the precursor gases. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)