The origin of a peak in the reststrahlen region of SiC

A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.     

Notes on the plasma resonance peak employed to determine doping in SiC

The doping level of a semiconductor material can be determined using the plasma resonance frequency to obtain the carrier concentration associated with doping. This paper provides an overview of the procedure for the three most common polytypes of SiC. Results for 3C-SiC are presented and discussed. In phosphorus doped samples analysed, it is submitted that the 2nd plasma resonance cannot be detected due to high values of the free carrier damping constant γ.     

The influence of the band structure of epitaxial graphene on SiC on the transistor characteristics

We fabricated high-mobility field-effect transistors based on epitaxial graphene synthesized by vacuum graphitization of both the Si- and C-faces of SiC. Room-temperature field-effect mobilities >4000 cm²/V s for both electrons and holes were achieved, although with wide distributions. By using a high-k gate dielectric, we were able to measure the transistor characteristics in a wide carrier density range, where the mobility is seen to decrease as the carrier density increases. We formulate a simple semiclassical model of electrical transport in graphene, and explain the sublinear dependence of conductivity on carrier density from the view point of the few-layer graphene energy band structure. Our analysis reveals important differences between the few-layer graphene energy dispersions on the SiC Si- and C-faces, providing the first evidence based on electrical device characteristics for the theoretically proposed energy dispersion difference between graphene synthesized on these two faces of SiC.     

The stability of SiC coating and SiO2/SiC multilayer on the surface of graphite for HTGRs at normal service condition

The stability of SiC coating in helium with a low concentration of O₂, CO₂, and H₂O is a key factor for their application in improvement of oxidation resistance of graphite for high temperature gas-cooled reactors (HTGRs). Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC is partial pressure of active gas in helium; the critical temperature of passive oxidation for SiC increases with the partial pressure of O₂, CO₂, and H₂O, SiC is prone to undergo active oxidation in He–CO₂ and He–H₂O system. SiO₂/SiC multilayer coating can improve the oxidation resistance of graphite at higher temperature than SiC coating does under normal operation condition for HTGRs.     

Band-gap modulation of graphane-like SiC nanoribbons under uniaxial elastic strain

The band-gap modulation of zigzag and armchair graphane-like SiC nanoribbons (GSiCNs) under uniaxial elastic strain is investigated using the density functional theory. The results show that band gap of both structures all decreases when being compressed or tensed. In compression, both zigzag and armchair GSiCNs are semiconductors with a direct band gap. However, in tension, the armchair GSiCNs undergo a direct-to-indirect band-gap transition but the zigzag GSiCNs still have a direct band gap. These results are also proved by HSE06 method. This implies a potential application of the graphane-like SiC nanoribbons in the future pressure sensor and optical electronics nanodevices.     

掺铝3C-SiC电子结构的第一性原理计算及其微波介电性能

采用基于密度泛函理论的第一性原理平面波超软赝势法,对比研究了未掺杂和Al掺杂3C-SiC材料的电子结构和介电常数.结果表明:Al掺杂后,Fermi能级进入价带,带隙宽度略为加宽,在8.2—12.4 GHz范围内介电常数大幅度增大.利用燃烧合成法制备了Al掺杂的3C-SiC粉体吸收剂,通过矢量网络分析仪测试了样品在8.2—12.4 GHz范围内的微波介电常数,验证了理论计算结果,并讨论了微波损耗机理.     

Measurement of the directional emittance of polycrystalline beryllium oxide

The spectral emittance of polycrystalline beryllium oxide has been measured at four different angles from 0° to 75°, at a temperature of 150°C. From the spectral measurements the average band emittance in the 8–13 μm window has been calculated. The results show that the band emittance decreases from 0.44 at the angle of 0°, down to 0.23 at an angle 75° off the normal. The low band emittance is caused by a strong reststrahlen band in the wavelength region 9.2–14 μm. This reststrahlen band has been modelled by a Lorentz one-oscillator model. Experiment and calculations show that this band of low emittance increases its width towards shorter wavelengths at inclined angles and covers almost the entire upper atmospheric window 8–13 μm at the angle of 75°.     

Lattice vibrations and optical properties of wurtzite InN in the reststrahlen region

The lattice vibrations and optical properties of wurtzite InN are studied by the first-principle calculations based on the density functional theory. The phonon spectra of lattice vibration are calculated under the Generalized-Gradient Approximation (GGA). The optical properties are investigated based on the phonon spectra. The phonon dispersion curve and the phonon density of state are calculated and compared with the existing experimental data. The calculation indicates that InN has a metal-like behavior. Our calculation shows that the fundamental vibration is therefore infrared active in wurtzite structure semiconductors.     

Operational improvement of AlGaN/GaN HEMT on SiC substrate with the amended depletion region

In this paper, a high performance AlGaN/GaN High Electron Mobility Transistor (HEMT) on SiC substrates is presented to improve the electrical operation with the amended depletion region using a multiple recessed gate (MRG–HEMT). The basic idea is to change the gate depletion region and a better distribution of the electric field in the channel and improve the device breakdown voltage. The proposed gate consists of lower and upper gate to control the channel thickness. Also, the charge of the depletion region will change due to the optimized gate. In addition, a metal between the gate and drain including the horizontal and vertical parts is used to better control the thickness of the channel. The breakdown voltage, maximum output power density, cut-off frequency, maximum oscillation frequency, minimum noise figure, maximum available gain (MAG), and maximum stable gain (MSG) are some parameters for designers which are considered and are improved in this paper.     

The defect impacts of zigzag SiC nanoribbons in the spin devices

In this work, electronic structures and spin transport characteristics of SiC zigzag nanoribbons with defects have been studied by spin-polarized first-principles calculations. It is found that the transport channel of the zigzag SiC nanoribbon device in parallel configurations is located in the edge of nanoribbons. The spin currents can be turned on or off by specific edge defects. As to the antiparallel configuration, all the SiC nanoribbon devices exhibit a perfect dual spin filtering effect, which is immune to the position of defects. By transmission spectra calculations, the corresponding mechanisms of these peculiar effects were explained. The results from this work might indicate a promising pathway for developing spin filters with SiC nanoribbons.     

AlC,SiC基态分子结构与分析势能函数的量子力学计算

用密度泛函理论的B3LYP方法和二次组态相互作用(QCISD(T))方法,选择6-31G(d,p)、6-311 G(2df,2pd)、6-311 G(3df,3pd)、cc-PVTZ、AUG-cc-PVTZ基组,优化计算了AlC和SiC分子基态的能量,平衡结构,谐振频率.根据原子分子反应静力学原理,导出了AlC和SiC分子基态的合理离解极限和离解能.通过优化计算结果和实验数据的对比,选择QCISD(T)/6-311 G(3df,3pd)方法对AlC和SiC分子基态的势能面进行了单点能扫描.采用最小二乘法拟合得到了AlC和SiC分子基态的Murell-Sor-bie势能函数.同时计算了光谱参数(Be,eα,ωe,ωeχe)和力常数(f2,f3,f4),并与实验结果进行比较.结果表明,计算结果与实验数据吻合的较好.     

碳化硅合成反应动力学研究

基于经典轨迹法研究了碳化硅合成反应C(3Pg) SiO(X1∑ ,V=0,1;J=0)→SiC(X1∑ ) O(3Pg)的动力学.该反应存在阈能,反应截面均存在一个极大值和最佳反应能量.当SiO(X1∑ )分别处于V=0、J=0和V=1、J=0状态时,反应阈能分别约为1.2552×103kJ.mol-1和1.1297×103kJ.mol-1,反应截面极大值分别为5.3742×10-3nm2和5.1824×10-3nm2,而最佳初始碰撞能Et(the Optimal InitialCollision Translation Energy)分别为3.3472×103kJ.mol-1和3.7656×103kJ.mol-1.在SiC的最佳产率区(即最佳反应能区),通过反应物的振动激发并不能使SiC产率明显提高,因此基态下SiC合成反应的最佳能区即为该反应的最佳产率区.     

Simulations of monolayer SiC transistors with metallic 1T-phase MoS2 contact for high performance application

We preform a first-principles study of performance of 5 nm double-gated (DG) Schottky-barrier field effect transistors (SBFETs) based on two-dimensional SiC with monolayer or bilayer metallic 1T-phase MoS₂ contacts. Because of the wide bandgap of SiC, the corresponding DG SBFETs can weaken the short channel effect. The calculated transfer characteristics also meet the standard of the high performance transistor summarized by international technology road-map for semiconductors. Moreover, the bilayer metallic 1T-phase MoS₂ contacts in three stacking structures all can further raise the ON-state currents of DG SiC SBFETs in varying degrees. The above results are helpful and instructive for design of short channel transistors in the future.     

SiC外延层表面化学态的研究

用高分辨X射线光电子能谱仪(XPS)和傅里叶变换红外(FTIR)光谱仪研究了SiC外延层表面的组分结构. XPS宽扫描谱,红外掠反射吸收谱及红外镜面反射谱的解析结果说明SiC外延层表面是由Si—O—Si和Si—CH₂—Si聚合体构成的非晶SiC_xO_y:H. SiC外延层表面的化学态结构为Si(CH₂)₄,SiO(CH₂)₃,SiO₂(CH₃)₂,SiO₃(CH₃),Si—Si,游离H₂O,缔合OH,Si—OH,O和O₂. 根据化学态结构和元素电负性确定了化学态的各原子芯电子束缚能顺序,并与XPS窄扫描谱拟合结果相对比,建立了化学态与其束缚能的对应关系,进而用Si(CH₂)₄的实际C 1s束缚能值进行校正,确定了各化学态的束缚能. 结果发现,除了SiC_xO_y(x=1,2,3,4,x+y=4)的Si 2p束缚能彼此不同外,其C 1s和O 1s彼此也不相同,其中SiO₂(CH₃)₂和SiO₃(CH₃)的C 1s束缚能与CH_m和C—O中C 1s的相近,对此从化学态结构,元素电负性和邻位效应进行了解释. 关键词： SiC 化学态 XPS FTIR     

碳化硅表面的外延Graphene

Graphene具有优异的电学性质,是非常有前途的纳米电子材料,有希望替代硅成为下一代集成电路材料.尽管目前有很多种制备Graphene的方法,但就Graphene在将来集成电路方面的应用而言,在碳化硅上的外延生长法最具潜力.文章首先从Graphene的能带结构开始,简单介绍为什么Graphene具有诸多优异的电学性质,比如异常霍尔效应、室温下的高迁移率、碳纳米管的弹道输运等.然后介绍这种外延生长方法及其发展现状.通过比较在不同碳化硅晶面和在不同条件下生长的Graphene的表面形貌,得出结论,在加热炉内     

包覆燃料颗粒碳化硅层的Raman光谱研究

本文研究了球床高温气冷堆燃料元件中包覆颗粒碳化硅层的Raman光谱. 通过分析不同制备条件下的碳化硅层断面的Raman光谱的峰位、半高全宽与强度, 明确了包覆颗粒中碳化硅层的晶相特征、密度变化和剩余应力等物性.通过分析不同密度碳化硅层一级Raman峰的同步、异步二维相关谱, 发现其LO模较TO模对于密度变化的响应更敏感. 这些结论为研究球床高温气冷堆燃料元件包覆颗粒中碳化硅层的结构及其物性有指导意义.     

SiC多型体几何结构与电子结构研究

采用平面波超软赝势法和范数不变赝势法对几种SiC多型体的几何结构、能带结构等进行了系统的研究.结果表明:6HSiC导带最低点在ML线上U点,用平面波超软赝势法计算时U点在(0000,0500,0176)点附近;而用范数不变赝势法计算时在导带最低点附近能带呈现不连续点,不连续点出现在(0000,0500,0178)点附近.两种赝势法计算结果相比,用平面波超软赝势法得到的导带最低点位置更靠近布里渊区M(0,05,0)点.在平面波超软赝势下,随着六角度的增加,cp,cpa增大的趋势较为明显,能隙和价带宽度变宽的趋势也较为明显.在计算极限内,绝对零度下4HSiC系统能量最低、最稳定,而Ewald能量显示3CSiC最稳定. 关键词： 密度泛函理论 电子结构 SiC     

SiC过渡层制备温度对碳化硅/氟化类金刚石复合薄膜血液相容性的影响

以316L不锈钢为基底,SiC晶体为靶材,Ar为源气体,采用磁控溅射法在不同温度下制备出系列SiC过渡层.然后以高纯石墨作靶,Ar和CHF_3为源气体,在同一工艺条件下再续镀一层氟化类金刚石(F-DLC)薄膜,形成SiC/F-DLC复合薄膜.研究表明,相比于F-DLC薄膜,复合薄膜的附着力显著增加,血液相容性明显改善.通过样品的拉曼和红外光谱分析了不同温度下制备的SiC过渡层以及复合薄膜结构的演变.结果表明,控制SiC过渡层制备温度可以有效调制过渡层中C=C键的比例以及—C—C—不饱和键的密度,复合薄膜中保留较高比例的芳香环式结构以及合适的F/C比是薄膜的血液相容性得以进一步改善的原因,SiC过渡层制备温度控制在500℃左右效果尤为明显.SiC薄膜和F-DLC两种薄膜的界面处形成一定比例的Si—C键和C=C键是导致复合薄膜附着力显著上升的直接原因.适当条件下在316L不锈钢和F-DLC薄膜之间增加SiC过渡层对于增强薄膜的附着力、改善其血液相容性是可行、有效的.     

多孔硅衬底上溅射沉积SiC:Tb薄膜的光致发光行为

在多孔硅衬底上用射频溅射法沉积了非晶的SiC:Tb薄膜. 对样品在N2中进行了不同温度的退火处理. 用傅里叶红外变换谱分析了样品的结构.用荧光光谱仪测试了样品的光致发光，在紫外、可见光区域观测到了强的发光峰.发现随着衬底加热温度和样品退火温度的变化，发光峰有明显的强度变化和微弱的蓝移现象.分析了产生这种现象的机理，得出了紫外区域的发光峰是由于氧缺乏中心引起的，而可见区的发光是由于Tb离子产生的. 关键词： 碳化硅 光致发光 氧缺乏中心 多孔硅     

Island-growth of SiCGe films on SiC

SiCGe ternary alloys have been grown on SiC by hot-wall low-pressure chemical vapour deposition. It has been found that the samples cxhibit an island configuration, and the island growth of SiCGe epilayer depends on the processing parameters such as the growth temperature. When the growth temperature is comparatively low, the epilayer has two types of islands： onc is spherical island; another is cascading triangular island. With the increase of the growth temperature, the islands change from spherical to cascading triangular mode. The size and density of the islands depend on the growth duration and GeH4 flow-rate. A longer growth time and a larger GeH4 flow-rate can increase the size and density of the island in thc initial stage of the epitaxy. In our case, The optimal growth for a high density of uniform islands occurred at a growth temperature of 1100℃ for l-minute growth, with 10 SCCM GeH4, resulting in a narrow size distribution （about 30nm diameter） and high density （about 3.5 ×10^10 dots/cm2）. The growth follows Stranski- Krastanov modc （2D to 3D modc）, both of the islands and the 2D growth layer have face-centred cubic structure, and the critical thickness of the 2D growth layer is only 2.5 nm.[第一段]