B-Al共掺杂3C-SiC的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势法,计算了未掺杂,B,Al单掺杂和B-Al共掺杂的3C-SiC的晶格参数、能带结构、态密度、有效质量、载流子浓度和电阻率. 计算结果表明：掺杂后导带和价带都向高能端移动,价带移动速度更快一些,使得禁带宽度都有一定程度的减小,其中B-Al共掺杂的禁带宽度最窄,纯净3C-SiC的禁带宽度最宽;B掺杂会减小价带顶空穴的有效质量,Al掺杂则反之,B-Al共掺杂补偿了二者的差异,和未掺杂的3C-SiC价带顶空穴的有效质量很接近. B和Al作为受主杂质,会极大地提高价带顶空穴载流子的浓度,而且B-Al共掺杂的3C-SiC的价带空穴浓度是B,Al单掺杂时的3倍. 4种体系中,B-Al共掺杂得到的电阻率是最低的,同单掺杂相比具有明显的性能优势. 关键词： 3C-SiC B-Al共掺杂 电阻率 第一性原理     

Fabrication and characteristics of a surface acoustic wave UV sensor based on ZnO thin films grown on a polycrystalline 3C-SiC buffer layer

Zinc oxide (ZnO) thin films were deposited onto a polycrystalline (poly) 3C-SiC buffer layer for surface acoustic wave (SAW) ultraviolet (UV) sensing using a magnetron sputtering system. X-ray diffraction (XRD) and photoluminescence (PL) spectra showed that the ZnO film grown on 3C-SiC/Si had a dominant c-axis orientation, a lower residual stress, and higher intensity of luminescence at 380 nm of ZnO thin film. The SAW resonator UV detector were fabricated on ZnO/Si structures with a 3C-SiC buffer layer. The SAW resonator exposed under UV illumination had a linear response with sensitivity of 85 Hz/(μW/cm²) in ZnO/3C-SiC/Si structures, as compared to 25 Hz/(μW/cm²) in ZnO/Si structures with UV intensity varied until 600 μW/cm².     

Al-N共掺杂3C-SiC介电性质的第一性原理计算

采用基于密度泛函理论的第一性原理平面波超软赝势法,建立了未掺杂,Al,N单掺杂和Al-N共掺杂3C-SiC的4种超晶胞模型,并分别对模型进行了几何结构优化,对比研究了其能带结构,态密度分布和介电常数.计算结果表明:Al掺杂会增大SiC的晶格常数,而N对SiC的晶格影响很小.Al掺杂会导致费米能级进入价带,使3C-SiC成为p型半导体,且带隙宽度略为加宽.N掺杂后的SiC其导带和价带均向低能端发生移动,带隙稍有减小.本征3C-SiC几乎不具备微波介电损耗性能.但是可以通过进行Al掺杂或N掺杂加以改善,Al掺杂后的效果尤为突出.计算发现Al-N共掺杂后的3C-SiC材料在8.2—12.4 GHz范围内其微波介电损耗性能急剧下降,与实验结果相符合,并对这一结果进行了讨论分析.     

Scattering mechanisms and anomalous conductivity of heavily N-doped 3C-SiC in ultraviolet region

Using the first-principles density functional method, we investigate the band structures and conductivity spectra for N-doped 3C-SiC. It is found that conductivity peaks of heavily N-doped 3C-SiC are observed in the ultraviolet (UV), visible and infrared (IR) regions while the peaks can be only seen in the UV region for 3C-SiC. In the UV region, the conductivity peaks of 3C-SiC are obviously higher than those of N-doped 3C-SiC. According to the data of band structures, we calculate the ionized impurity scattering, inter-carrier scattering and neutral impurity scattering. The calculation results show that the scattering by incomplete ionization N to electrons and inter-carrier scattering have large effect on the conductive behavior of heavily N-doped 3C-SiC at room temperature. In the UV region, the conductivity of 3C-SiC depends on long-wavelength optical wave scattering, which has a longer relaxation time than that inter-carrier scattering and neutral scattering. This is the reason of anomalous conductivity of N-doped 3C-SiC in the UV region.     

正轴6H-SiC 衬底上3C-SiC薄膜的低压化学气相沉积生长

活性的O-和OH-被认为在苯酚形成过程中起了重要作用．通过低压化学气相沉积，在正轴6H-SiC(0001)衬底上沉积了3C-SiC薄膜，X射线衍射表明薄膜结晶质量良好．研究了生长参数对生长速率的影响，发现硅烷及其分解产物的输运是薄膜生长的限定因素．用原子力显微镜观察薄膜的表面形貌．这些结果表明薄膜的生长符合S-K方式．     

Electronic structure and magnetic properties of(Cu,N)-codoped3C-SiC studied by first-principles calculations

The electronic structures and magnetic properties of the Cu and N codoped 3C-Si C system have been investigated by the first-principles calculation.The results show that the Cu doped Si C system prefers the anti-ferromagnetic(AFM) state.Compared to the Cu doped system,the ionicities of C–Cu and C–Si in Cu and N codoped Si C are respectively enhanced and weakened.Especially,the Cu and N codoped Si C systems favor the ferromagnetic(FM) coupling.The FM interactions can be explained by virtual hopping.However,higher N concentration will weaken the ferromagnetism.In order to keep the FM interaction,the N concentration should be restricted within 9.3% according to our analysis.     

Simultaneous control of nanocrystal size and nanocrystal-nanocrystal separation in CdS nanocrystal assembly

We report an easy, one pot synthesis to prepare ordered CdS nanocrystals with varying inter-particle separation and characterize the particle separation using x-ray diffraction at low and wide angles.     

Raman scattering studies of polycrystalline 3C-SiC deposited on SiO2 and AlN thin films

This paper describes the Raman scattering characteristics of the Raman spectra of 0.4- and 2.0-μm-thick polycrystalline (poly) 3C-SiC on AlN /Si and SiO₂/Si by using atmosphere pressure chemical vapor deposition (APCVD) with hexamethyldisilane (HMDS) and carrier gases (Ar+H₂). In the Raman spectra for all growth temperatures, the D and G peaks of nanocrystalline graphite were measured. The C/Si rate of poly 3C-SiC deposited in (Ar+H₂) atmosphere was higher than that in H₂ gas, although HMDS C/Si rate is 3. The biaxial stresses of 2.0-μm-thick 3C-SiC on SiO₂ and AlN, which was deposited at the growth temperature of 1180 °C after annealing AlN at 800 and 1100 °C, were calculated as 428 and 896 MPa, respectively. Therefore, poly 3C-SiC should admix with nanocrystalline graphite due to the addition of Ar gas and poly 3C-SiC on SiO₂ should be better than on AlN for harsh environmental MEMS applications.     

Effects of annealing temperature on the electrical property and microstructure of aluminum contact on n-type 3C–SiC

The 3C-SiC thin films used herein are grown on Si substrates by chemical vapor deposition. A1 contacts with differ- ent thickness values are deposited on the 3C-SiC/Si （100） structure by the magnetron sputtering method and are annealed at different temperatures. We focus on the effects of the annealing temperature on the ohmic contact properties and mi- crostructure of A1/3C-SiC structure. The electrical properties of A1 contacts to n-type 3C-SiC are characterized by the transmission line method. The crystal structures and chemical phases of A1 contacts are examined by X-ray diffraction, Raman spectra, and transmission electron microscopy, respectively. It is found that the A1 contacts exhibit ohmic contact behaviors when the annealing temperature is below 550 ℃, and they become Schottky contacts when the annealing tem- perature is above 650 ℃. A minimum specific contact resistance of 1.8 × 10-4 Ω cm2 is obtained when the A1 contact is annealed at 250 ℃.     

3C-SiC薄膜小角晶界附近位错核心的原子组态研究

用LaB₆灯丝200 kV高分辨透射电镜拍摄了有小角晶界的3C-SiC/(001)Si 薄膜的[110]高分辨电子显微像. 用像解卷技术把本不直接反映晶体结构的实验像转化为结构像. 首先, 从完整区的结构像中分辨开间距仅为0.109 nm的Si和C原子柱; 随后按赝弱相位物体近似像衬理论, 分析像衬随晶体厚度的变化规律, 辨认出Si和C原子; 进而在原子水平上得出小角晶界附近两个复合位错的核心结构, 构建了结构模型并计算了模拟像. 实验像与模拟像的一致程度验证了结构模型的正确性. 于是, 在已知完整晶体结构的前提下, 仅从一帧实验高分辨像出发, 推演出原子的种类和位错核心的原子组态. 还讨论了3C-SiC 小角晶界的形成与晶界附近出现复合位错的关系.     

B、N单掺杂3C-SiC电子结构和光学性质的第一性原理研究

采用第一性原理的密度泛函理论赝势平面波方法,计算了未掺杂与B、N单掺杂3C-SiC的电子结构和光学性质.结果表明:掺杂改变了3C-SiC费米面附近的电子结构;B掺杂使得禁带宽度减小,价带顶上移,费米能级进入价带,形成p型半导体;N掺杂使得禁带宽度减小,导带底下移,费米能级进入导带,形成n型半导体.B、N掺杂均提高了3C-SiC在低能区的折射率、消光系数和吸收系数,增强了对红外光谱的吸收.     

含有缺陷3C-SiC陶瓷拉伸性能的分子动力学模拟

SiC纤维增韧SiC基复合材料(SiC_f/SiC)由于其优越的性能而成为新一代核能系统重要候选材料之一.材料中的缺陷会使材料的力学性能发生变化,本文运用分子动力学程序LAMMPS模拟计算了分别含有空位、微空洞和反位替代三种缺陷的3C-SiC结构体系沿[100]方向的拉伸变形过程,原子间相互作用采用Tersoff多体势描述.通过模拟得到不同缺陷体系的应力—应变曲线和拉伸过程中体系能量,通过分析应力-应变曲线,得到了不同缺陷体系的杨氏模量、断裂应变、拉伸强度随缺陷"浓度"的变化关系,最后分析了3C-SiC拉伸断裂机理.研究结果表明,空位和微空洞对杨氏模量、拉升强度的影响类似,都是随着缺陷"浓度"的增加而减小,反位替代缺陷使体系的杨氏模量随缺陷"浓度"的增加而增大.     

5 μm thick 3C-SiC layers grown on Ge-modified Si(100) substrates

The effect of the germanium coverage prior to the epitaxial growth of 5 μm thick 3C-SiC on Si(100) substrates were evaluated with Atomic Force Microscopy and μ-Raman spectroscopy. The 3C-SiC layers were grown by atmospheric pressure chemical vapor deposition via a special procedure leading to layers with compressive instead of tensile stress. The Ge amount was varied from 0 up to 2 ML. The obtained results showed that the residual stress inside the layers is shifted in the compressive direction; the crystalline quality is improved with the Ge introduction but on the account of the surface roughness. These results open the route for the use of Ge-modified Si(100) as a potential substrate in order to improve the heteroepitaxial growth of 3C-SiC on silicon substrates.     

“Temperature oscillation” as a real-time monitoring of the growth of 3C-SiC on Si substrate

Pyrometric interferometry has been observed during gas-source molecular beam epitaxy (GSMBE) of 3C-SiC on Si substrate using monomethyl silane. The period of the “temperature oscillation” is shown to correspond to λ/2n, with the λ and n being the wavelength used in the monochromatic optical pyrometry and the refractive index of the grown film, respectively. As is the case for other heteroepitaxies, pyrometric interferometry may provide a feasible real-time monitoring method for the growth of 3C-SiC film on Si substrates.     

3C-SiC Heteroepitaxial Growth on Silicon: The Quest for Holy Grail

For a long time now, 3C-SiC has attracted attention of the semiconductor community due to its very interesting properties. The lack of commercial 3C-SiC seeds for epitaxy has forced researchers to prospect for different host materials in order to grow heteroepitaxial thin layers. Because of the obvious economical and technical advantages, silicon is a very attractive substrate so that more than 90% of the thin 3C-SiC heteroepitaxial films are grown on such seed. However, the obstacles to overcome, mainly lattice and thermal mismatch, are challenging. This article reviews the numerous attempts for growing high quality 3C-SiC heteroepitaxial layers on silicon substrate. The various aspects of the heteroepitaxial growth, from substrate carbonization to epitaxy, are discussed as a function of growth parameters. The difficulties encountered and the proposed solutions are described. Perspectives of this heteroepitaxial system are proposed.     

Si(100)衬底上n-3C-SiC/p-Si异质结构研究

利用LPCVD方法在Si(100)衬底上获得了3C-SiC外延膜,扫描电子显微镜(SEM)研究表明3C-SiC/p-Si界面平整、光滑,无明显的坑洞形成。研究了以In和Al为接触电极的3C-SiC/p-Si异质结的I-V,C-V特性及I-V特性的温度依赖关系,比较了In电极的3C-SiC/p-Si异质结构和以SiGe作为缓冲层的3C-SiC/SiGe/p-Si异质结构的I-V特性,实验发现引入SiGe缓冲层后,器件的反向击穿电压由40V提高到70V以上。室温下Al电极3C-SiC/p-Si二极管的最大反向击穿电压接近100V,品质因子为1.95。     

Comparison of ZnO thin films grown on a polycrystalline 3C-SiC buffer layer by RF magnetron sputtering and a sol-gel method

Zinc oxide (ZnO) thin films were deposited on a polycrystalline (poly) 3C-SiC buffer layer using RF magnetron sputtering and a sol-gel method. The post-deposition annealing was performed on ZnO thin films prepared using both methods. The formation of ZnO piezoelectric thin films with less residual stress was due to a close lattice mismatch of the ZnO and SiC layers as obtained by the sputtering method. Nanocrystalline, porous ZnO film prepared using the sol-gel method showed strong ultraviolet UV emission at a wavelength of 380 nm. The 3C-SiC buffer layer improved the optical and piezoelectric properties of the ZnO film produced by the two deposition methods. Moreover, the different structures of the ZnO films on the 3C-SiC intermediate layer caused by the different deposition techniques were also considered and discussed.     

Si(100)和蓝宝石(0001)衬底上3C-SiC的Raman研究

单晶Si和蓝宝石(0001)是两种重要的3C-SiC异质外延衬底材料，然而，由于Si及蓝宝石和3C-SiC之间大的晶格失配度和热膨胀系数失配度，在3C-SiC中会产生很大的内应力，直接影响3C-SiC的电学特性。Raman散射测试是一个功能很强的测试方法，其强度、宽度、Raman位移等有关Raman参数可以给出有关SiC晶体质量的信息，其中包括内应力。利用背散射几何构置的Raman方法研究了Si(100)和蓝宝石(0001)村底上LPCVD方法生长的SiC外延薄膜，在生长的所有样品中均观察到了典型的3C-SiC的TO和LO声子峰，在3C-SiC／Si材料中，这两个声子峰分别位于970．3cm-l和796．0cm-1，在3C-SiC／蓝宝石材料中，分别位于965．1cm^-1和801．2cm-1，这一结果表明这两种外延材料均为3C-SiC晶型。利用一个3C-SiC自由膜作为无应力标准样品,并根据3C-SiC／Si和3C-SiC／蓝宝石的TO和LO声子峰Raman位移相对于自由膜的移动量，得到3C-SiC中的内应力约分别为1GPa和4GPa。实验发现在这两种材料的TO声子峰的Raman位移移动方向相反，通过比较3C-SiC、Si和蓝宝石的热膨胀系数，预期Si衬底上的3C-SiC外延膜受到的应力为张应力，而蓝宝石衬底上3C-SiC受到的应力则为压应力。     

InSb纳米晶体的生长和吸收光谱的研究

采用在惰性气体中蒸发的方法获得了沉积在ZnS基片上的InSb纳米晶体,其平均尺寸随惰性气体的压强增加而增大.从实验测量的室温吸收谱上看到,当纳米晶体的平均直径从27.9 nm减小到24.2nm再到21.4 nm时,其吸收边分别向高能方向移动了0.0151 eV和0.0145 eV.用有效质量近似模型计算了半导体纳米晶体的吸收边相对其体材料的移动,将理论计算与实验结果进行了比较.     

A simple and versatile mini-arc plasma source for nanocrystal synthesis

Nanocrystals in the lower-nanometer-size range are attracting growing interest due to their unique properties. A simple and versatile atmospheric direct current mini-arc plasma source has been developed to produce nanoparticles as small as a few nanometers. The nanoparticles are formed by direct vaporization of solid precursors followed by a rapid quenching. Both semiconductor tin oxide and metallic silver nanoparticles have been produced at rates of 1–10 mg/h using the mini-arc source. Transmission electron microscopy and X-ray diffraction analyses indicate that most nanoparticles as produced are nonagglomerated and crystalline. Size distributions of nanoparticles measured with an online scanning electrical mobility spectrometer are broader than the self-preserving distribution, suggesting that the nanoparticle growth is coagulation-dominated, and that the particles experience a range of residence times. The electrical charges carried by as-produced aerosol nanoparticles facilitate the manipulation of nanoparticles. The new mini-arc plasma source hence shows promise to accelerate the exploration of nanostructured materials.