AlN/Si(100)上CVD SiC薄膜的光致发光谱

本工作用化学气相淀积方法在AlN/Si(100)复合衬底上生长SiC薄膜.外延生长过程中,采用C4H4和SiH4作为反应气源,H2作为载气.样品的X-射线衍射谱和拉曼散射谱显示,所得到的外延层为六角对称的SiC薄膜.俄歇电子能谱及X-射线光电子能谱的测量结果表明,在外延膜中存在来自衬底的Al和N元素.样品的光致发光测量显示,所有的样品均可在室温下观察到位于3.03eV和3.17eV处的发光峰,这分别相应于4H-SiC能带中电子从导带到Al受主能级之间的辐射跃迁和电子从N施主能级到价带之间的辐射跃迁,从而表明所得的外延薄膜的多形体为4H-SiC.     

热丝CVD法在单晶硅衬底上低温外延生长Si和Ge薄膜的研究

采用热丝CVD法在单晶Si衬底上进行了Si和Ge 薄膜的低温外延生长,用XRD和Raman谱对其结构性能进行了分析.结果表明:在衬底温度200 ℃时,Si(111)单晶衬底上外延生长出了Raman峰位置为521.0 cm-1;X射线半峰宽(FWHM)为5.04 cm-1.结晶质量非常接近于体单晶的(111)取向的本征Si薄膜;在衬底温度为300 ℃时,在Si(100)单晶衬底上异质外延,得到了Raman峰位置为300.3 cm-1的Ge薄膜,Ge薄膜的晶体取向为Ge(220).研究表明热丝CVD是一种很好的低温外延薄膜的方法.     

硅基上Si1-xGex合金的外延生长及性能研究

硅基上高质量的异质外延生长是实现高性能微电子器件的基础,本文通过低温分子束外延技术在Si衬底上实现了全组分的Si1-x Gex(0相似文献   

不同衬底表面上大晶粒多晶Si薄膜的制备

利用高频感应加热化学气相沉积(HFCVD)工艺,以H2稀释的SiH4作为反应气体源,分别在n-(111)Si衬底上常规热生长的SiO2层、织构的SiO2层和纳米晶粒多晶Si薄膜表面上,制备了具有均匀分布的大晶粒多晶Si膜.采用扫描电子显微镜(SEM)和X射线衍射(XRD)等检测手段,测量和分析了沉积膜层的表面形貌、晶粒尺寸、密度分布与择优取向等结构特征.结果表明,多晶Si膜中Si晶粒的尺寸大小和密度分布不仅与衬底温度、SiH4浓度与反应气压等工艺参数有关,而且强烈依赖于衬底的表面状态.本实验获得的最好的薄膜中,Si晶粒平均尺寸约为2.3 μm,密度分布约为3.8×107/cm2.对薄膜的沉积机理分析表明,衬底表面上Si原子基团的吸附、迁移、成核与融合等热力学过程支配着大晶粒多晶Si膜的生长.     

在Si和GaAs衬底上分子束外延CdTe的晶格应变

本文利用高分辨率多重晶多重反射X射线衍射技术对分子束外延CdTe(211)B/ Si(211)与CdTe(211)B/GaAs(211)B材料的CdTe外延薄膜进行了倒易点二维扫描,并通过获得的倒易点二维图,对CdTe缓冲层的应力和应变状况进行了分析.研究显示,对于一定厚度的CdTe外延薄膜,在从生长温度280℃降至室温20℃的过程中,由于和衬底存在热膨胀系数的差异,将在外延薄膜中产生热应力,使外延薄膜发生应变,并且这种应变取代了失配应变,在晶格畸变中占据主导地位.对于Si衬底,热应变表现为张应力;对于GaAs衬底,热应变表现为压应力.该研究结果对于进一步优化在大失配的异质衬底上外延同Hg1-xCdxTe材料晶格匹配的Cd1-yZnyTe材料的Zn组分具有指导意义.     

SiCN薄膜在Si衬底上的沉积

本文采用微波等离子体化学气相沉积(MPCVD)系统,在单晶Si衬底上制备出了SiCN薄膜.所采用的源气体为高纯CH4和N2,而Si源来自于Si衬底、SiH4和Si棒.用场发射扫描电镜(SEM)、X射线光电子能谱(XPS)和X射线衍射谱(XRD)对样品进行了表征与分析.结果表明,外加Si源、高的衬底温度、高流量N2有助于提高样品的成膜质量.所得到SiCN样品是新型的六方结构三元化合物.     

利用Al/AlAs中间层调控GaAs在Si(111)上外延生长的研究

为了实现Ⅲ-V器件在硅基平台上单片集成,近年来Ⅲ-V半导体在硅衬底上的异质外延得到了广泛研究。由于Ⅲ-V半导体与Si之间大的晶格失配以及晶格结构不同,在Si上生长的Ⅲ-V半导体中存在较多的失配位错及反相畴,对器件性能造成严重影响。而Si(111)表面的双原子台阶可以避免Ⅲ-V异质外延过程中形成反相畴。本文利用分子束外延技术通过Al/AlAs作为中间层首次在Si(111)衬底上外延生长了GaAs(111)薄膜。通过一系列对比实验验证了Al/AlAs中间层的插入对GaAs薄膜质量的调控作用,并在此基础上通过低温-高温两步法优化了GaAs的生长条件。结果表明Al/AlAs插层可以为GaAs外延生长提供模板,并在一定程度上释放GaAs与Si之间的失配应力,从而使GaAs薄膜的晶体质量得到提高。以上工作为Ⅲ-V半导体在硅上的生长提供了新思路。     

基于正交实验的100 mm4°偏轴SiC衬底外延均匀性研究

采用行星热壁式SiC外延炉对100 mm 4°偏轴4H-SiC衬底外延工艺进行了研究.分析了氢气预刻蚀工艺对4°偏轴衬底外延材料表面形貌的影响.采用双指标正交实验,通过极差分析的方法研究了C/Si比、Cl/Si比、主氢流量、生长温度、三路气体比等工艺参数对SiC外延厚度和掺杂浓度均匀性指标影响的主次顺序,并给出了优化的外延参数.采用该工艺条件制得的无台阶聚集形貌的SiC外延片片内厚度均匀性和浓度均匀性分别是1.23;和3.32;.     

Bi4Ti3O12铁电薄膜X射线光电子能谱研究

本文采用化学溶液沉积(CSD)工艺在Si(100)衬底上制备了Bi4Ti3O12铁电薄膜,这种薄膜的X射线衍射(XRD)结果显示其具有较好的结晶性.运用X射线光电能谱仪(XPS)对薄膜的结构进行了研究,分析结果表明,衬底中Si向镀在其上的Bi4Ti3O12膜层内扩散,影响扩散的主要因素是膜厚及退火温度.     

退火温度和β-FeSi2薄膜厚度对n-β-FeSi2/p-Si异质结太阳电池的影响

本文采用室温直流磁控溅射Fe-Si组合靶的方法,并通过后续退火温度的优化得到了单一相高质量的β-FeSi2薄膜.结果表明,在本实验条件下得到的未掺杂的β-FeSi2薄膜在室温下是n型导电的,其电学特性存在一个退火温度的最优点:800 ℃.而且在这个最佳温度点上,在Si(111)衬底上外延得到的薄膜载流子迁移率比在Si(100)上高出了一倍多.在上述研究的基础上,采用p-Si(111)单晶片作为外延生长β-FeSi2薄膜的衬底,并通过退火温度和薄膜厚度的优化制备出了国内第一个n-β-FeSi2/p-Si异质结太阳电池,其Jsc=7.90 mA/cm2 ,Voc=0.21 V,FF=0.23,η=0.38;.     

Preparation and Characterization of MBE-grown Si/CaF2 Heterostructures

Growth and fabrication of silicon-on-insulator structures, based on heteroepitaxial growth of insulating films on Si, is an area of research that has rapidly developed in recent years. Thin CaF₂ films and Si/CaF₂ multilayers were prepared on {111}-oriented Si substrates by molecular beam epitaxy (MBE) and were investigated by RHEED and RBS. For epitaxial growth the Si substrates were cleaned using the ultraviolet/ozone surface cleaning method which is an effective tool to remove contaminants from the surface by low-temperature in-vacuo preheating. The growth of CaF₂ on such Si{111} substrates provides epitaxial layers with a high structural perfection. When this layer system, however, is used as a substrate for epitaxial Si growth the Si layers show always twin formation. Si layers without twins could be obtained only after deposition of thin amorphous Si buffer layers at room temperature, immediately followed by Si growth at 700 °C.     

表面预处理对SiO2/Si结构上APCVD生长SiC薄膜的影响

采用S iH4-C3H8-H2气体反应体系在S iO2/S i复合衬底上进行了S iC薄膜的APCVD生长。实验结果表明,H2表面预处理温度过高或时间过长会导致衬底表面S iO2层熔化再结晶或被腐蚀掉。通过“先硅化再碳化”的工艺方法可以较好地解决S iO2/S i复合衬底上S iC成核困难以及粘附性差的问题,同时还可以有效抑制S iO2中的O原子向S iC生长膜扩散。选择预处理温度和薄膜生长温度为1180℃、H2预处理、S iH4硅化和C3H8碳化时间均为30 s的最佳生长条件时,可以得到<111>晶向择优生长的多晶3C-S iC外延薄膜,薄膜生长速率约为2.0~2.5nm/m in.     

Dependence of chemical composition and bonding of amorphous SiC on deposition temperature and the choice of substrate

Amorphous SiC has superior mechanical, chemical, electrical, and optical properties which are process dependent. In this study, the impact of deposition temperature and substrate choice on the chemical composition and bonding of deposited amorphous SiC is investigated, both 6 in. single-crystalline Si and oxide covered Si wafers were used as substrates. The deposition was performed in a standard low-pressure chemical vapour deposition reactor, methylsilane was used as the single precursor, and deposition temperature was set at 600 and 650 °C. XPS analyses were employed to investigate the chemical composition, Si/C ratio, and chemical bonding of deposited amorphous SiC. The results demonstrate that these properties varied with deposition temperature, and the impact of substrate on them became minor when deposition temperature was raised up from 600 °C to 650 °C. Nearly stoichiometric amorphous SiC with higher impurity concentration was deposited on crystalline Si substrate at 600 °C. Slightly carbon rich amorphous SiC films with much lower impurity concentration were prepared at 650 °C on both kinds of substrates. Tetrahedral Si-C bonds were found to be the dominant bonds in all deposited amorphous SiC. No contribution from Si-H/Si-Si but from sp² and sp³ C-C/C-H bonds was identified.     

4H-SiC衬底表面SiC薄膜的同质外延生长

以4H-SiC为衬底,在不同衬底温度下进行SiC薄膜的同质外延生长。利用反射式高能电子衍射(RHEED)、扫描电子显微镜(SEM)、拉曼(Raman)等测试手段,对生长样品的结构和结晶质量进行了表征。根据测试结果发现,在衬底温度为1200℃时能够得到质量较高的薄膜,在另外两个温度(1100℃和1300℃)条件下得到的薄膜质量是较差的。     

Annealing effects of highly homogeneous a-Si1−xCx:H

We report the effect of annealing on the properties of amorphous hydrogenated silicon carbide thin films. The samples were deposited onto different substrates by plasma enhanced chemical vapor deposition at temperatures between 300 and 350 °C. The gaseous mixture was formed by silane and methane, at the ‘silane starving plasma regime’, and diluted with hydrogen. Rutherford backscattering and Fourier transform infrared spectrometry were used, respectively, to determine the atomic composition and chemical bonds of the samples. The film’s structure was analyzed by means of X-ray absorption fine structure and X-ray diffraction. For temperatures higher than 600 °C, amorphous silicon carbide films annealed under inert atmosphere (Ar or N₂) clearly changed their structural and compositional properties due to carbon loss and oxidation, caused by the presence of some oxygen in the annealing system. At 1000 °C, crystallization of the films becomes evident but only stoichiometric films deposited on single crystalline Si[1 0 0] substrates presented epitaxial formation of SiC crystals, showing that the crystallization process is substrate dependent. Films annealed in high-vacuum also changed their structural properties for annealing temperatures higher than 600 °C, but no traces of oxidation were observed or variations in their silicon or carbon content. At 1200 °C the stoichiometric films are fully polycrystalline, showing the existence of only a SiC phase. The XANES signal of samples deposited onto different substrates and annealed under high-vacuum also show that crystallization is highly substrate dependent.     

Effect of AlN doping on the growth morphology of SiC

AlN doped SiC films were deposited on on‐axis Si‐face 4H‐SiC (0001) substrates by the physical vapor transport (PVT) method. Thick film in the range of 20 μm range was grown and morphology was characterized. Films were grown by physical vapor deposition (PVD) in a vertical geometry in the nitrogen atmosphere. We observed that nucleation occurred in the form of discs and growth occurred in hexagonal geometry. The X‐ray studies showed (001) orientation and full width of half maxima (FWHM) was less than 0.1° indicating good crystallinity. We also observed that film deposited on the carbon crucible had long needles with anisotropic growth very similar to that of pure AlN. Some of the needles grew up to sizes of 200 μm in length and 40 to 50 μm in width. It is clear that annealing of SiC‐AlN powder or high temperature physical vapor deposition produces similar crystal structure for producing AlN‐SiC solid solution. SEM studies indicated that facetted hexagons grew on the top of each other and coarsened and merged to form cm size grains on the substrate. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of the Substrate Crystals upon the Structure of Thermal Oxide Layers on Si

Comparisons of Bragg reflections from thermal oxide thin films on Si wafers were made for five sets of samples with various kinds of substrates. The intensities of the reflections for the samples with the substrate of better quality were stronger than those of poor one, indicating that the structures of the crystalline SiO₂ in the oxide layer were related with the quality of the Si substrates. It is also shown that no diffraction peaks were observed from the oxide layers grown on Si substrates by chemical vapor deposition.     

Influence of substrate and film thickness on structural,optical and electrical properties of ZnO thin films

Transparent Zinc Oxide (ZnO) thin films have been grown on Si (100) and Sapphire (0001) substrates by RF magnetron sputtering for different growth time intervals (10, 30 and 60 min) to study the substrate and thickness effects. All the films have been grown at a substrate temperature of 450 °C. It has been found that the average growth rate on Si (100) substrate (8.6 nm/min) is higher than that on Sapphire (0001) substrate (2.6 nm/min) in an identical growth condition which clearly shows the virtual role of substrates. The lower growth rate on Sapphire (0001) suggests that the increasingly ordered and uniform growth due to less lattice mismatch. The grown films have been characterized by X‐ray diffraction (XRD), Reflectance, Photoluminescence (PL) and Hall measurements. The XRD result (FWHM) reveals that for lower growth time, the films grown on Si (100) is better than on Sapphire (0001). Conversely, for higher growth time, the films grown on Sapphire (0001) is better than on Si (100). The variation of strain behavior due to thickness on both substrates has been justified by UV‐Vis reflectance, photoluminescence and Hall effect measurements. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarities of AlN films and underlying 3C-SiC intermediate layers grown on (1 1 1) Si substrates

The hydride vapor phase epitaxy (HVPE) of {0 0 0 1} AlN films on {1 1 1} Si substrates covered with epitaxial {1 1 1} cubic SiC (3C-SiC intermediate layers) was carried out. 3C-SiC intermediate layers are essential to obtain high-quality AlN films on Si substrates, because specular AlN films are obtained with 3C-SiC intermediate layers, whereas rough AlN films are obtained without 3C-SiC intermediate layers. We determined the polarities of AlN films and the underlying 3C-SiC intermediate layers by convergent beam electron diffraction (CBED) using transmission electron microscopy. For the first time, the polarities of the AlN films and the 3C-SiC intermediate layers were determined as Al and Si polarities, respectively. The AlN films were hardly etched by aqueous KOH solution, thereby indicating Al polarity. This supports the results obtained by CBED. The result is also consistent with electrostatic arguments. An interfacial structure was proposed. The 3C-SiC intermediate layers are promising for the HVPE of AlN films on Si substrates.     

不同能量密度下脉冲激光烧蚀制备纳米Si晶粒成核生长动力学研究

在室温、10 Pa氩气环境下,采用脉冲激光烧蚀(PLA)技术,通过改变激光能量密度,在烧蚀点正下方、与烧蚀羽辉轴线平行放置的衬底上沉积制备了一系列纳米Si晶薄膜.采用SEM、Raman散射谱和XRD对纳米Si晶薄膜进行了表征.结果表明:沉积在衬底上的纳米Si晶粒分布在距靶一定的范围内,晶粒尺寸随与靶面距离的增加先增大后减小;随着激光能量密度的增加,晶粒在衬底上的沉积范围双向展宽,但沉积所得最大晶粒尺寸基本保持不变,只是沉积位置随激光能量密度的增加相应后移.结合流体力学模型、成核分区模型和热动力学方程,通过模拟激光烧蚀靶材的动力学过程,对纳米Si晶粒的成核生长动力学过程进行了研究.