碳化温度对异质外延3C-SiC薄膜结晶质量及表面形貌的影响

本文以Si(100)为衬底,利用水平式常压冷壁化学气相沉积(APCVD)系统在不同温度(1100～1250℃)下制备的“缓冲层”上生长了3C-SiC薄膜.结果表明,薄膜为外延生长的单一3C-SiC多型,薄膜表面呈现“镶嵌”结构特征,Si/3C-SiC界面平整无孔洞.碳化温度对薄膜的结晶质量和表面粗糙度有显著的影响,当碳化温度低于或高于1200℃时,薄膜的结晶质量有所降低,且随着碳化温度的升高,薄膜表面粗糙度呈现增大的趋势.当在1200℃下制备的“缓冲层”上生长薄膜时,可以获得最优质量的3C-SiC外延膜,其(200)晶面摇摆曲线半峰宽约为0.34°,表面粗糙度约为5.2nm.     

衬底温度对In2S3薄膜结构及其性能的影响

采用超声喷雾热解法,在玻璃基底上一步合成了In2S3薄膜.研究了衬底温度对In2S3薄膜的结构、表面形貌、电学和光学性能影响.结果表明:所制备的In2S3薄膜均具有沿(220)面择优取向生长特性且无其他杂相,衬底温度对薄膜的均匀性、致密度、结晶程度均有明显影响,并因此影响薄膜的光电性能.薄膜的导电件随着衬底温度的升高迅速增强,但足在衬底温度为350℃时有所降低.衬底温度为300℃所制备的薄膜在可见光区透光率最高达到90;以上,禁带宽度达到2.43 eV.     

SiC衬底上β-Ga2O3薄膜生长及p-SiC/n-β-Ga2O3异质结光伏特性

本文采用脉冲激光沉积(PLD)技术在p型4H-SiC衬底上,制备出沿(403)择优生长的β-Ga₂O₃薄膜。结果表明,衬底生长温度对β-Ga₂O₃薄膜的形貌、结构、组分,以及生长机理都有重要影响。当生长温度由300 ℃升高至500 ℃时,薄膜结晶质量随生长温度升高而提高,当温度进一步升高到600 ℃时,薄膜结晶质量变差,这是由于在相对低温(500 ℃以下)阶段,生长温度越高,沉积在衬底上原子的动能越大,越容易迁移,使得β-Ga₂O₃薄膜主要按照二维生长模式进行生长,薄膜结晶质量提高,表现为随着生长温度升高,粗糙度降低。但当温度上升到600 ℃时,由于4H-SiC衬底和β-Ga₂O₃薄膜之间的热膨胀系数存在差异,导致薄膜生长由主要以二维生长模式向三维岛状演变。基于p-4H-SiC/n-β-Ga₂O₃构筑的异质结太阳电池,其标准测试条件下光电转换效率达到3.43%。     

衬底温度对电子辅助增强化学气相沉积金刚石膜的影响

本工作采用蒙特卡罗(Monte Carlo)方法,对以CH4/H2为源气体的电子助进化学气相沉积(EACVD)金刚石薄膜的气相动力学过程进行了模拟.提出了衬底温度的空间梯度变化模型,研究了衬底温度对EACVD气相过程中的电子群行为以及H2和CH4分解过程的影响.结果表明:电子平均温度随着衬底温度的升高而升高;当气压较低时,分解得到的成膜关键粒子H、CH3数量随衬底温度的增大而减少;而当气压较高时,H、CH3数目随衬底温度的增大而增大;衬底温度主要改变了衬底表面附近的化学反应动力学过程,从而对薄膜质量产生了决定性的影响.     

衬底温度对氢化微晶硅锗薄膜生长的影响

采用VHF-PECVD技术在玻璃衬底上沉积微晶硅锗薄膜.研究了衬底温度对微晶硅锗薄膜的微结构和光电特性的影响.结果表明:随着衬底温度的升高,微晶硅锗薄膜的生长速率减小,(220)晶向强度增强;而同一衬底温度下,锗浓度的增加将抑制薄膜(220)晶向的生长,通过相应地提高衬底温度可以解决这一问题.利用生长基团在薄膜生长表面的扩散理论对实验结果进行了解释.     

衬底温度对共蒸发制备GaSb多晶薄膜性质的影响

采用共蒸发的方法在玻璃衬底上制备出GaSb多晶薄膜材料.研究了薄膜生长速率与衬底温度、Ga源温度和Sb源温度的关系.通过XRD、UV-Vis、Hall效应和AFM等测试方法,研究了衬底温度对于GaSb薄膜的结构特性、光电性质以及表面形貌的影响.GaSb多晶薄膜具有(111)择优取向,薄膜的吸收系数达到105 cm-1,晶粒尺寸随衬底温度升高逐渐增大;衬底温度为540℃时,薄膜的迁移率达到127 cm2/V·s,空穴浓度为3×1017 cm-3.GaSb薄膜的表面粗糙度随温度增加而增加.     

磁控溅射衬底加热温度和后退火温度对制备β-Ga2O3薄膜材料的影响

作为宽禁带半导体材料的一员,结构稳定的β-Ga₂O₃具有比SiC和GaN更宽的禁带宽度和更高的巴利加优值,近年来受到科研人员的广泛关注。本文采用射频(RF)磁控溅射法在C面蓝宝石衬底上生长β-Ga₂O₃薄膜,探究溅射过程中衬底加热温度的影响。溅射完成后通过高温退火处理提升薄膜质量,研究衬底加热温度和后退火温度对氧化镓薄膜晶体结构和表面形貌的影响。利用X射线衍射(XRD)、原子力显微镜(AFM)等测试手段对β-Ga₂O₃薄膜晶体结构、表面形貌等进行分析表征。实验结果表明,随着衬底加热温度的升高,β-Ga₂O₃薄膜表面粗糙度逐渐降低,薄膜晶体质量得到显著提升;在氧气气氛中进行后退火,合适的后退火温度有利于氧化镓薄膜重新结晶、增大晶粒尺寸,能够有效修复薄膜的表面态和点缺陷,对于改善薄膜晶体质量有明显优势。     

晶格失配和退火氧压对La_(0.825)Ca_(0.175)MnO_3薄膜的电学性能的影响（英文）

采用紫外脉冲激光沉积技术分别在LaA lO 3(LAO)、(LaA lO 3)0.3-(SrA lT aO 6)0.7(LSAT)和SrT iO 3(STO)(001)单晶衬底上制备了La0.825Ca0.175MnO 3(LCMO)薄膜。实验发现衬底的晶格失配度和退火氧压对薄膜结晶质量和电学性能有重要影响。电阻-温度曲线显示,生长在LAO(压应变)的LCMO薄膜比生长在STO(拉伸应变)的薄膜有更高的绝缘体-金属转变温度Tp和更大的电阻温度系数(TCR)。增加退火氧压可以有效地提高薄膜的Tp和TCR值。当退火氧压为30000 Pa时,与衬底晶格失配度最小的LCMO/LSAT薄膜具有最高的Tp(234.5 K)和最大的TCR(22.4%)。实验结果表明Ca含量为0.175的La1-xCaxMnO 3薄膜材料在测辐射热计等方面有潜在的应用前景。     

(111)择优取向ZnS薄膜的制备及特性研究

采用激光分子束外延技术在Al2O3衬底上成功外延生长了ZnS薄膜.用X射线衍射、扫描电子显微镜和光致发光谱表征了衬底温度对薄膜结构、形貌和光学特性的影响.结果表明所生长的ZnS薄膜为闪锌矿,具有(111)择优长向,随衬底温度的升高,X射线衍射峰的半高宽先减小后增大,在衬底温度为300℃时,半高宽最窄.薄膜结构致密,表面不平整度随衬底温度的升高而增大.薄膜的带隙随衬底温度的升高出现蓝移,可见光区域透射率最高达到98;,在360 nm激发波长下,观测到402 nm和468 nm两个发光带,衬底温度为300℃时,发光最强.     

热壁外延制备InAs/Si(211)薄膜及其电学性能研究

采用热壁外延(Hot Wall Epitaxy,HWE)沉积系统在单晶Si(211)衬底表面制备了InAs薄膜,研究了不同生长温度(300℃、350℃、400℃、450℃和500℃)对薄膜材料结构及其电学性能的影响.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)、霍尔(Hall)测试等,对InAs/Si(211)薄膜的晶体结构、表面形貌及电学参数进行了测试分析.结果表明:采用HWE技术在Si(211)衬底表面成功制备了InAs薄膜,薄膜具有闪锌矿结构并沿(111)方向择优生长.随着生长温度从300℃升高到500℃,全峰半高宽(FWHM)先减小后增大,生长温度为400℃时薄膜的晶粒尺寸最大为73.4 nm,载流子浓度达到1022 cm-3,霍尔迁移率数值约为102 cm2/(V·s),说明优化生长温度能够降低InAs薄膜的缺陷复合,使薄膜结晶质量和电学性能得到提高.SEM及AFM的测试结果显示由于较高的晶格失配及Si衬底斜切面(211)的特殊取向,在Si(211)衬底上生长的InAs薄膜主要为三维层加岛状(S-K)生长模式,表面粗糙度(Ra)随温度的升高先减小后增大,400℃时薄膜的平均表面粗糙度Ra为48.37 nm.     

MEMS用Si台面及SiO2/Si衬底上3C-SiC的LPCVD生长

本文报道用在Si台面及热氧化SiO2衬底上3C-SiC薄膜的LPCVD生长,反应生长使用的气体为SiH4和C2H4,载气为H2,采用光学显微镜、X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电镜（SEM）、以及室温Hall测试对所生长的3C—SiC材料进行了测试与分析,结果表明在3C-SiC和SiO2之间没有明显的坑洞形成。     

硅基片上异质外延SiC的机理研究

本文利用低压高温MOCVD系统,成功地在Si(111)基片上外延出了具有高质量的SiC薄膜,并对其反应机理做了一些初步的研究.大部分观点认为,SiC/Si的异质外延,其最初的状态应该为Si衬底中Si的扩散.但是,本文通过在不同流量比的条件下,SiC薄膜在Si基片以及Al2O3基片上外延的比较,发现在SiC/Si的异质外延过程中起重大作用的并非Si衬底中Si的扩散,而是很大程度上作用于C向Si衬底的扩散.同时,还发现反应速率的快慢受SiH4流量所限制.当SiH4流量增加时,反应速率会明显加快,但是结晶质量会相对变差.     

Growth of cubic silicon carbide on oxide using polysilicon as a seed layer for micro-electro-mechanical machine applications

The growth of highly oriented 3C–SiC directly on an oxide release layer, composed of a 20-nm-thick poly-Si seed layer and a 550-nm-thick thermally deposited oxide on a (1 1 1)Si substrate, was investigated as an alternative to using silicon-on-insulator (SOI) substrates for freestanding SiC films for MEMS applications. The resulting SiC film was characterized by X-ray diffraction (XRD) with the X-ray rocking curve of the (1 1 1) diffraction peak displaying a FWHM of 0.115° (414″), which was better than that for 3C–SiC films grown directly on (1 1 1)Si during the same deposition process. However, the XRD peak amplitude for the 3C–SiC film on the poly-Si seed layer was much less than for the (1 1 1)Si control substrate, due to slight in-plane misorientations in the film. Surprisingly, the film was solely composed of (1 1 1) 3C–SiC grains and possessed no 3C–SiC grains oriented along the 3 1 1 and 1 1 0 directions which were the original directions of the poly-Si seed layer. With this new process, MEMS structures such as cantilevers and membranes can be easily released leaving behind high-quality 3C–SiC structures.     

Electron microscopy studies of epitaxial MgB2 superconducting thin films grown by in situ reactive evaporation

The morphology and chemistry of epitaxial MgB₂ thin films grown using reactive Mg evaporation on different substrates have been characterized by transmission electron microscopy methods. For polycrystalline alumina and sapphire substrates with different surface planes, an MgO transition layer was found at the interface region. No such layer was present for films grown on MgO and 4-H SiC substrates, and none of the MgB₂ films had any detectable oxygen incorporation nor MgO inclusions. High-resolution electron microscopy revealed that the growth orientation of the MgB₂ thin films was closely related to the substrate orientation and the nature of the intermediary layer. Electrical measurements showed that very low resistivities (several μΩ cm at 300 K) and high superconducting transition temperatures (38 to 40 K) could be achieved. The correlation of electrical properties with film microstructure is briefly discussed.     

纳米晶粉体加入量对CSBT陶瓷厚膜结构及性能的影响

采用粉末溶胶法和快速层层退火工艺,在Pt/Ti/SiO2/Si基片上制备了钙锶铋钛(CSBT)陶瓷厚膜.研究了纳米晶粉体加入量对钙锶铋钛陶瓷厚膜结构及性能的影响.结果表明:纳米晶粉体加入量在较宽的范围内可以制备出高质量的钙锶铋钛厚膜,厚膜的显微结构及铁电性能对粉末的加入量比较敏感,适当的加入量有利于促使厚膜晶粒的a轴择优取向,从而有利于膜的铁电性能.当粉末加入量为7.5 g/100 mL时,钙锶铋钛陶瓷厚膜晶粒出现a轴择优取向,剩余极化和矫顽场强分别为6.3 μC/cm2和57 kV/cm,具有较高的应用价值.     

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)     

MgTiO3对Mg2SiO4-SiC复相材料烧结性能的影响

在采用传统固相法预合成Mg2SiO4和MgTiO3粉体的基础上,在H2气氛下常压烧结制备了Mg2SiO4-MgTiO3-SiC复相材料。研究了Mg2SiO4和MgTiO3的最佳原料配比及MgTiO3的添加量、烧结温度、保温时间对复相材料烧结性能和相组成的影响。结果表明:Mg2SiO4粉的最佳Mg/Si物质的量比为2.02,MgTiO3粉的最佳Mg/Ti物质的量比为1,Mg2SiO4-MgTiO3-SiC复相材料的相组成为Mg2SiO4、MgTiO3和6H-SiC;MgTiO3的加入可促进材料烧结,最佳保温时间为1 h。     

Al2O3膜层制备参数对SiO2/Al2O3/PET复合膜透湿性能的影响

采用磁控溅射工艺在PET衬底上依次沉积了Al2 O3和SiO2薄膜,制备出SiO2/Al2 O3/PET复合膜.利用扫描电镜和透湿仪对复合膜的表面形貌和透湿性能进行表征.研究了制备Al2 O3膜层的射频功率、氩气流量、本底真空度和溅射时间4个参数对复合膜透湿率的影响.结果表明:复合膜的透湿率随着本底真空度的升高而减小,随着射频功率、氩气流量和溅射时间的增加均呈现先减小后增大的变化趋势;4个制备参数对复合膜透湿率的影响程度由大到小依次是本底真空度、氩气流量、射频功率、溅射时间;4个制备参数的较优组合为本地真空度0.5×10-3 Pa,射频功率300 W,溅射时间6 min,氩气流量70 mL·min-1.     

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。     

MOCVD growth of GaN on Si(1 1 1) substrates using an ALD-grown Al2O3 interlayer

GaN thin films have been grown on Si(1 1 1) substrates using an atomic layer deposition (ALD)-grown Al₂O₃ interlayer. This thin Al₂O₃ layer reduces strain in the subsequent GaN layer, leading to lower defect densities and improved material quality compared to GaN thin films grown by the same process on bare Si. XRD ω-scans showed a full width at half maximum (FWHM) of 549 arcsec for GaN grown on bare Si and a FWHM as low as 378 arcsec for GaN grown on Si using the ALD-grown Al₂O₃ interlayer. Raman spectroscopy was used to study the strain in these films in more detail, with the shift of the E₂(high) mode showing a clear dependence of strain on Al₂O₃ interlayer thickness. This dependence of strain on Al₂O₃ thickness was also observed via the redshift of the near bandedge emission in room temperature photoluminescence (RT-PL) spectroscopy. The reduction in strain results in a significant reduction in both crack density and screw dislocation density compared to similar films grown on bare Si. Screw dislocation density of the films grown on Al₂O₃/Si substrates approaches that of typical GaN layers on sapphire. This work shows great promise for the use of oxide interlayers for growth of GaN-based LEDs on Si.