Si(100)衬底上PLD法制备高取向度AlN薄膜

采用脉冲激光沉积法(PLD),以KrF准分子为脉冲激光源,Si(100)为衬底,同时引 入缓冲层TiN和Ti_0.8Al_0.2N,制备了结晶质量优异的A1N薄膜,X射线衍射(XRD)及反射 式高能电子衍射(RHEED)分析表明A1N薄膜呈(001)取向、二维层状生长.研究发现,薄膜 的生长模式依赖于缓冲层种类,直接在Si衬底上或MgO／Si衬底上的A1N薄膜呈三维岛状生 长;而同时引入缓冲层TiN和Ti_0.8Al_0.2N时,A1N薄膜呈二维层状生长.此外,激光能量密 度大小对A1N薄膜的结晶性有显著的影响,激光能量密度过大,薄膜表面粗糙,有颗粒状沉积 物生成.在氮气气氛中沉积,能使薄膜的取向由(001)改变为(100).     

激光分子束外延

介绍了激光分子束外延(Laser Molecular Beam Epitaxy)的基本原理和技术特点,评述了激光分子束外延技术在超导材料和磁性材料方面所取得的主要成就,并给出了这种技术在材料科学领域的应用前景和发展潜力.     

SiO2/Si衬底制备ZnO薄膜及表征

本文报道了利用脉冲激光沉积技术在热氧化p型硅衬底上生长ZnO外延薄膜.引入高阻非晶SiO2缓冲层,有效地降低了检测过程中单晶衬底对ZnO薄膜的电学性能影响.利用XRD,SEM,Hall和PL对其进行研究.结果表明,在衬底温度为500℃时,生长的ZnO薄膜具有优良的晶体质量,电学性能和发光性能.     

脉冲激光沉积法在蓝宝石衬底上制备a轴取向YSZ薄膜

采用脉冲激光沉积方法,通过金红石相TiO2(200)纳米诱导层在蓝宝石衬底上生长了(200)取向的萤石相钇稳定氧化锆(YSZ)薄膜。通过反射式高能电子衍射对薄膜生长过程进行原位监测;用XRD分析进行后位的薄膜结构表征;使用原子力显微镜来观测薄膜的形貌及晶粒大小。结果表明,我们成功地在蓝宝石衬底上外延了具有三重旋转织构的a轴取向萤石相YSZ薄膜,其外延关系为YSZ(200)∥TiO2(200)∥Al2O3(0001);YSZ[010]∥TiO2[001]∥Al2O3[11-20]。     

Si(100)衬底上SiC的外延生长

在1050℃下用Si2H6和C2H4在Si(100)衬底上外延生长了3C-SiC,生长前只通入C2H4将Si衬底碳化形成SiC缓冲层.碳化过程中C2H4与Si表面反应形成了SiC孪晶,但随着生长时间的延长,外延层转变为单晶层,其表面呈现典型的单晶SiC的(2×1)再构.从外延层的Raman谱观察到明显的SiC的TO和LO声子模;SEM观测结果表明,外延层的表面比较平整.     

脉冲激光法外延生长锰氧化物薄膜

利用脉冲激光法在ＬａＡｌＯ３衬底上外延生长了Ｌａ－Ｃａ－Ｍｎ－Ｏ、Ｌａ－Ｓｒ－Ｍｎ－Ｏ等巨磁电阻薄膜,测定了这些薄膜电阻－温度特性,观测到了其铁磁转变及巨磁电阻效应,实验发现,较高的淀积温度使薄膜的峰值转变温度Ｔｐ降低,峰值电阻率增大,而高温后退火则具有相反的效果,分析比较了多种因素对薄膜生长与性能的影响及其机理。     

在GaAs(100)衬底上离化团束外延ZnSe单晶薄膜

ZnSe是一种理想的蓝紫色发光材料，用于制作发光器件有较大的应用前景，采用单源喷发、离化原子团束（ICB）技术在GaAs（100）上外延ZnSe单晶薄膜，并用电子能谱分析了外延薄膜的成分。用X射线衍射和RHEED研究了外延ZnSe单晶薄膜结构和外延质量。研究了淀积能量和衬底温度对薄膜质量的影响。得到了摆动曲线半高宽为133rad·s，并具有原子水平平整程度的ZnSe（100）单晶薄膜。外延薄膜存在0．2～0．4μm的应变过渡层，过渡层随淀积能量的增大而变薄。     

脉冲激光沉积法在Si(111)衬底上生长高c轴取向LiNbO3薄膜

在氧压20Pa,衬底温度600℃,靶材与衬底距离4cm的最优化条件下,利用脉冲激光沉积(PLD)技术首次在无诱导电压和任何缓冲层的情况下,在单晶Si(111)衬底上生长具有优良结晶品质和高c轴取向的LiNbO3晶体薄膜.利用X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)对LiNbO3薄膜的结晶品质,择优取向性以及表面形貌进行了系统的分析.结果表明生长出了具有优异晶体质量的c轴取向LiNbO3薄膜,表面光滑平整且无裂纹产生,表面粗糙度约4.8nm,有利于硅基光电子器件的制备和利用.     

脉冲激光薄膜制备技术

脉冲激光薄膜沉积是近年来受到普遍关注的制膜新技术。简要介绍了脉冲激光薄膜沉积技术的物理原理、独具的特点和研究发展动态,并介绍了采用脉冲激光薄膜沉积技术制备硅基纳米PtSi薄膜的结果     

在室温条件下制备高质量纳米结构TiN薄膜研究

在室温条件下,利用磁过滤等离子体在单晶硅和不锈钢表面上制备了性能优异的纳米结构TiN薄膜.运用原子力显微镜和掠角入射X射线衍射仪对其结构与形貌进行了表征,利用纳米压痕仪测量了TiN薄膜的硬度和弹性模量.结果表明:TiN薄膜表面光滑,致密,无柱状晶;TiN晶粒的平均尺寸为50nm,薄膜硬度达50 GPa,是传统CVD和PVD技术沉积氮化钛的两倍多;XRD衍射试验表明,纳米TiN的衍射角都普遍向小角度移动,TiN晶粒沿(111)择优生长.     

Room-temperature growth of AlN/TiN epitaxial multi-layer by laser molecular beam epitaxy

We have fabricated epitaxial AlN thin films at room temperature on sapphire (0001) substrates with a TiN (111) epitaxial buffer layer by pulsed laser deposition in ultra-high vacuum (laser molecular beam epitaxy method). The TiN buffer layers were also fabricated at room temperature. Four-circle X-ray diffraction analysis and reflection high-energy electron diffraction results indicate the heteroepitaxial structure of AlN (0001)/TiN (111)/sapphire (0001) with the epitaxial relationship of AlN [10-10]||TiN [11-2]||sapphire [11-20]. The surface of the room-temperature grown AlN film was found to be atomically flat, reflecting the nano-stepped surface of ultrasmooth sapphire substrates. Then, we could achieve the room-temperature epitaxial growth of [AlN/TiN] multi-layer. The temperature dependence of resistivity of the AlN/TiN multi-layer film was also measured.     

Deposition and characterization of MgO/Si gate stacks grown by molecular beam epitaxy

In this article, the deposition and characterization of amorphous MgO films grown on Si (001) using molecular beam epitaxy is reported. In order to ensure amorphous films, low substrate temperatures (200 °C) and high oxygen pressures were used (up to 5 × 10^− 3 Pa). Both atomic and molecular oxygen species were used at different pressures. Films ranging in thickness from 3 nm till 30 nm were grown and characterized using structural and electrical methods.The dielectric constant deduced from this thickness series corresponds to 8.74 close to the bulk value of 9.8. The best equivalent oxide thickness value observed for this series - grown under high oxygen pressure - corresponds to 1.2 nm for a current density measured at V_FB − 1 V of 0.1 A/cm². The films grown with atomic oxygen display a lower capacitance and lower leakage compared to the films grown using molecular oxygen. This is due to the appearance of a thin SiO₂ interface layer which is also responsible for the high defect density observed in the capacitance-voltage measurements. Upon annealing both types of films in forming gas for 15 min at 450 °C, the capacitance decreases further while the leakage increases. This change is assigned to the appearance of the lower bandgap (6.6 eV), lower dielectric constant (6.6) phase of silicate, MgSiO₃. Furthermore a V_FB shift of − 0.6 V is observed and is related to the appearance of oxygen vacancies as Mg diffuses into the SiO₂ interface layer.     

The preparation and characterization of preferred (110) orientation aluminum nitride thin films on Si (100) substrates by pulsed laser deposition

The preferred (110) oriented aluminum nitride (AlN) thin films have been prepared by pulsed laser deposition on p-Si (100) substrates. The films were characterized with X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscope (AFM). The results indicate that the AlN thin films are well-crystallized when laser energy is higher than 300 mJ/puls. The AFM images show that the surface roughness of the deposited AlN thin films gradually increases with increasing laser energy, but the surface morphologies are still very smooth. The crystallinity and morphology of the thin films are found to be strongly dependent on the laser energy.     

磁控溅射TiN薄膜的工艺及电学性能研究

采用反应直流磁控溅射法,在Si基底上制备TiN薄膜.研究了溅射沉积过程中溅射气压和Ar/N2气体流量比对TiN薄膜结构及其电学性能的影响,并对试验结果进行了分析.研究发现,在Ar/N2气体流量比为15:1时,TiN薄膜的表面均方根粗糙度和电阻率都为最小.当溅射气压增大时,薄膜厚度减小.当溅射气压为0.3～0.5Pa时,薄膜表面较光滑,电阻率较小.     

Crystal shape of GaAs nanocrystals deposited on Si(100) by molecular beam epitaxy

The shape changes in GaAs nanocrystals deposited on Si substrate have been studied as a function of the coverage by transmission electron microscopic observations in order to see the growth mechanism from the viewpoint of the surface energy and the lattice strain energy between the nanocrystal and the substrate. When GaAs was deposited on the Si(100) surface, the shape of the GaAs nanocrystals changes from stepped mound, hut cluster to dome structure with increasing the coverage. The shape changes are responsible for decreasing the total free energy caused by the lattice strain energy with the substrate and surface energy depending on the crystal size.     

Growth of stoichiometric TiO2 thin films on Au(100) substrates by molecular beam epitaxy

The present study reports on the growth of thin TiO₂ films onto Au(100) single crystals by Ti evaporation in a reactive O₂ atmosphere at two different substrate temperatures: room temperature (RT) and 300 °C. The growth of the oxide films was monitored by means of X-ray photoemission spectroscopy, while the valence and conduction band electronic structure was investigated by UV and inverse photoemission spectroscopy, respectively.The TiO₂ film grows epitaxially on the Au(100) substrate at 300 °C exhibiting the rutile (100) surface. The evolution of the Ti 2p lineshape with the oxide coverage shows the presence of reduced oxide species (characterized by Ti^3 + ions) at the Au(100) interface. A crystalline and stoichiometric TiO₂ oxide is produced at high substrate temperature, while growth at RT gives a measurable concentration of defects. Post growth annealing in ultra-high vacuum of the RT grown film increases this concentration, while subsequent annealing in O₂ atmosphere restores the sample to the as-grown conditions.     

Microstructure and optical properties of cubic AlN/TiN bilayers deposited by laser molecular beam epitaxy

AlN/TiN bilayers were deposited on Si(100) substrates with varying laser pulse energy by laser molecular beam epitaxy (LMBE) technique, and their growth mode, crystal structure and optical properties were investigated. The results indicated that atomically flat TiN single films and AlN/TiN bilayers with layer-by-layer growth mode were successfully grown on Si(100) substrates at optimal laser pulse energy. Both TiN and AlN in the grown bilayers exhibited the NaCl-type cubic structure with the same (200) preferred orientation, showing an excellent epitaxial relationship. TiN single film was more reflective in the infrared range and presented a small transparent window centered at wavelength of 404 nm. Reflectance spectrum of AlN film on top of TiN indicated the sharp absorption at about 246 nm, yielding a bandgap energy of 5.04 eV comparable to the theoretical calculation of bulk cubic AlN, but scarcely reported by the experimental data.     

Epitaxial growth of ZnO layers on (111) GaAs substrates by laser molecular beam epitaxy

ZnO layers were grown on (111) GaAs substrates by laser molecular epitaxy at substrate temperatures between 200 and 550 °C. X-ray diffraction analysis revealed that c-axis of ZnO epilayer with a wurtzite structure is perpendicular to the substrate surface. X-ray rocking curves and Raman spectroscopy showed that the crystal quality of ZnO epilayers depends on the substrate temperature during the growth. Strong near-band-edge emission in the UV region without any deep-level emissions was observed from the ZnO epilayers at room temperature. The results indicate that laser molecular beam epitaxy is a promising growth method for obtaining high-quality ZnO layers on (111) GaAs substrates.     

PLD工艺制备高质量ZnO/Si异质外延薄膜

采用脉冲激光沉积工艺在不同条件下以Si(111)为衬底制备了Zno薄膜.通过对不同氧压下(0～50Pa)沉积的样品的室温PL谱测试表明,氧气氛显著地提高了薄膜的发光质量,在50Pa氧气中沉积的ZnO薄膜具有最强的近带边UV发射.XRD测试说明在氧气氛中得到的薄膜结晶质量较差,没有单一的(002)取向.利用-低温(500℃)沉积的ZnO薄膜作缓冲层,得到了高质量的ZnO外延膜.与直接沉积的ZnO膜相比,生长在缓冲层上的ZnO膜展现出规则的斑点状衍射花样,而且拥有更强的UV发射和更窄的UV峰半高宽(98meV).对不同温度下沉积的缓冲层进行了RHEED表征,结果表明,在600～650℃之间生长缓冲层,有望进一步改善ZnO外延膜的质量.     

基于SVR的脉冲激光沉积TiN/AlN多层薄膜的工艺优化

根据脉冲激光沉积(PLD)法在单晶Si试样表面沉积制备多层TiN/AlN硬质膜实验数据,应用基于粒子群算法(PSO)寻优的支持向量回归(SVR)方法,建立不同工艺参数下沉积的TiN/AlN多层膜的AlN膜厚及TiN薄膜硬度的SVR预测模型。在相同的训练与测试样本集下,将SVR所得的AlN膜厚预测值与免疫径向基函数(IRBF)神经网络的计算结果进行比较。结果表明,SVR模型训练和预测结果的平均绝对百分误差要比IRBFNN模型的小,其预测精度更高,预测效果更好。应用SVR的TiN薄膜硬度模型对PLD法沉积TiN薄膜的工艺参数进行了优化,分析了多因素对PLD法沉积TiN薄膜硬度的交互作用和影响。该方法可为人们利用PLD法沉积TiN/AlN多层功能薄膜提供科学的理论指导,具有重要的理论意义和实用价值。