等离子增强原子层沉积低温生长GaN薄膜

采用等离子增强原子层沉积技术在低温下于单晶硅衬底上成功生长了Ga N多晶薄膜,利用椭圆偏振仪、低角度掠入射X射线衍射仪、X射线光电子能谱仪对薄膜样品的生长速率、晶体结构及薄膜成分进行了表征和分析.结果表明,等离子增强原子层沉积技术生长Ga N的温度窗口为210—270?C,薄膜在较高生长温度下呈多晶态,在较低温度下呈非晶态;薄膜中N元素与大部分Ga元素结合成N—Ga键生成Ga N,有少量的Ga元素以Ga—O键存在,多晶Ga N薄膜含有少量非晶态Ga_2O_3.     

原子层沉积方法制备核-壳型纳米材料研究

采用原子层沉积方法在碳黑纳米颗粒表面分别沉积Al₂O₃, ZnO, TiO₂和Pt, 成功制备出核-壳型纳米材料. 通过高分辨率透射电子显微镜、X射线光电子能谱仪、 能谱仪对材料的表面形貌、晶体结构、薄膜成分进行了表征和分析. 结果表明, 原子层沉积方法是制备核壳型纳米材料的理想方法. 此外, 还分析了采用原子层沉积方法沉积不同材料, 所生长的薄膜材料有单晶、多晶、非晶等多种存在形式的形成原因. 关键词： 原子层沉积 核-壳型纳米材料 碳黑纳米颗粒     

O2流量对磁控溅射N掺杂TiO2薄膜成分及晶体结构的影响

利用直流脉冲磁控溅射方法在室温下通过改变O₂流量制备具有不同晶体结构的N掺杂TiO₂薄膜,利用台阶仪、X射线光电子能谱仪、X射线衍射仪、紫外-可见分光光度计等设备对薄膜沉积速率、化学成分、晶体结构、禁带宽度等进行分析.结果表明:所制备的薄膜元素配比约为TiO_1.68±0.06N_0.11±0.01,N为替位掺杂,所有样品退火前后均未形成Ti—N相结构,N掺杂TiO₂薄膜的沉积速率、晶体结构等主要依赖于O₂流量.在O₂流量为2 sccm时,N掺杂TiO₂薄膜沉积速率相对较高,薄膜为非晶态结构,但薄膜内含有锐钛矿(anatase)和金红石(rutile)相晶核,退火后薄膜呈anatase和rutile相混合结构,禁带宽度仅为2.86 eV.随着O₂流量的增加,薄膜沉积速率单调下降,退火后样品禁带宽度逐渐增加.当O₂流量为12 sccm时,薄膜为anatase相择优生长,退火后呈anatase相结构,禁带宽度为3.2 eV.综合本实验的分析结果,要在室温条件下制备晶态N掺杂TiO₂薄膜,需在高O₂流量(＞10 sccn)条件下制备. 关键词： 2薄膜')" href="#">N掺杂TiO₂薄膜 磁控溅射 化学配比 晶体结构     

辉光放电等离子体辅助XeCl准分子激光溅射沉积碳氮薄膜

利用直流辉光放电等离子体辅助的脉冲激光沉积技术在Si衬底上生长了碳氮薄膜.通过扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱等多种手段,对薄膜的形貌、成分、晶体结构、价键状态等特性进行了分析和确定.结果表明,沉积薄膜为含有非晶SiN和晶态氮化碳颗粒结构,晶态成分呈多晶态,主要为α-C₃N₄相、β-C₃N₄相,晶粒大小为40—60nm.碳氮之间主要以C-N非极性共价键形式相结合. 关键词： 脉冲激光沉积 直流辉光放电 碳氮薄膜     

FeMn掺杂AlN薄膜的制备及其特性研究

采用直流磁控共溅射技术, 以Ar与N₂为源气体, 硅片为衬底成功地制备了Fe, Mn掺杂AlN薄膜. 利用X射线衍射和拉曼光谱研究了工作电流、靶基距离等工艺参数的改变对薄膜结构的影响. 利用扫描电子显微镜和能谱分析仪对薄膜的表面形貌和组成成分进行了分析. 利用振动样品磁强计在室温下对Fe, Mn掺杂AlN薄膜进行了磁性表征. Mn掺杂AlN薄膜表现出顺磁性的原因可能是由于Mn掺杂浓度较高, 在沉积过程部分Mn以团簇的形式存在, 反铁磁性的Mn团簇减弱了体系的铁磁交换作用. Fe掺杂AlN薄膜表现出室温铁磁性, 这可能是AlFeN三元化合物作用的结果. 随着Fe 掺杂AlN薄膜中Fe原子浓度从6.81%增加到16.17%, 其饱和磁化强度M_s由0.27 emu·cm^-3逐渐下降到0.20 emu·cm^-3, 而矫顽力H_c则由57 Oe增大到115 Oe (1 Oe=79.5775 A/m), 这一现象与Fe离子间距离的缩短及反铁磁耦合作用增强有关. 关键词： 直流磁控共溅射 氮化铝薄膜 结构 磁性     

多层纳米AlGaN薄膜制备及其场发射性能

本文采用激光脉冲沉积系统在SiC基底上制备了GaN/AlN/GaN多层纳米结构薄膜,探索了多层纳米薄膜量子结构增强场发射性能.X射线衍射和扫描电子显微镜结果表明,已成功制备出了界面清晰、结晶良好的GaN/AlN/GaN多层纳米薄膜.场发射测试结果表明:多层纳米薄膜结构相对于GaN和AlN单层纳米薄膜,其场发射性能得到显著提升.其开启电场低至0.93V/μm,电流密度在5.5V/μm时已经能够达到30mA/cm~2.随后进一步分析了纳米结构增强场发射机理,电子在GaN/AlN/GaN多层纳米薄膜结构中的量子阱中积累使其表面势垒高度显著下降,并通过共振隧穿效应进一步提高电子的透过概率,从而使场发射性能极大提高.研究结果将为应用于高性能场发射器件的纳米薄膜材料的制备提供一种好的技术方案.     

原子层沉积与聚焦离子束切片法制备X射线波带片

针对X射线波带片对大高宽比的应用需求,采用原子层沉积法在光滑的金属丝表面生长膜厚可高精度控制的多层膜环带结构,再利用聚焦离子束切片技术获得大高宽比的多层膜X射线波带片。采用复振幅叠加法设计了以Al₂O₃/HfO₂分别为明环和暗环材料的X射线波带片,实验上利用原子层沉积在直径为72μm的金丝表面交替沉积了10.11μm的Al₂O₃/HfO₂多层膜,环带数为356,总直径为92.22μm,最外环宽度为25 nm。通过聚焦离子束切割得到高为1.08μm、高宽比达43∶1的X射线多层膜菲涅耳波带片。该波带片应用于上海光源(BL08U1A)软X射线成像线站时,在1.2 keV X射线下实现聚焦成像功能,展现出利用该技术制备多层膜X射线波带片的潜力。     

AlN/Si3N4纳米多层膜的外延生长与力学性能

采用射频磁控溅射方法制备单层AlN, Si₃N₄薄膜和不同调制周期的AlN/Si₃N₄纳米多层膜.采用X射线衍射仪、高分辨透射电子显微镜和纳米压痕仪对薄膜进行表征.结果发现,多层膜中Si₃N₄层的晶体结构和多层膜的硬度依赖于Si₃N₄层的厚度.当AlN层厚度为4.0nm、 Si₃N₄层厚度 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 应力场 超硬效应     

激光分子束外延BaTiO3薄膜最顶层表面原子平面与薄膜生长机理

用激光分子束外延技术在SrTiO₃(001)衬底上外延生长了高质量的BaTiO_{3< /sub>薄膜,薄膜的生长过程由反射式高能电子衍射仪(RHEED)原位实时监测,表明薄膜具有 二维层状生长模式.薄膜的晶体结构和表面形貌分别由X射线衍射和原子力显微镜表征,显示 该薄膜为完全c轴取向四方相晶体结构,其表面具有原子尺度光滑性.采用角分辨X射线光电 子谱技术(ARXPS),研究了BaTiO3薄膜表面最顶层原子种类和排列状况.结果表 明,BaTiO3 关键词： 激光分子束外延 3薄膜')" href="#">氧化物BaTiO3薄膜 最顶层表面 角分辨X射线光电子谱}     

原子层沉积制备铱薄膜的特性研究

以乙酰丙酮铱[Ir(acac)3]和高纯氧为前驱体,采用原子层沉积(ALD)方法在基板温度为340℃的石英玻璃和硅基板上制备了金属铱薄膜。采用反射光谱测试仪、X射线电子能谱(XPS)、X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)等手段对不同厚度薄膜的微结构、表面形貌和光学性能进行了研究。结果表明,原子层沉积制备的Ir薄膜中元素纯度较高(大于95%),表面粗糙度低,并呈现多晶纳米颗粒。同时,Ir薄膜在紫外波段表现出较好的光学特性,可以用于制作Ir金属紫外光栅等光学器件。     

Characterization of hetero-interfaces between group III nitrides formed by PLD and various substrates

We have grown group III nitride epitaxial films on various substrates by pulsed laser deposition and investigated structural properties of the surfaces and the hetero-interfaces using grazing incidence angle X-ray reflectivity (GIXR) and atomic force microscopy (AFM). It has been found that hetero-interfaces between PLD AlN and conventional substrates such as Al₂O₃ and Si are quite abrupt (about 0.5 nm) probably due to a less reactive growth ambience. However, we observed a thin interfacial layer (less than 10 nm) at the hetero-interface between AlN and (Mn,Zn)Fe₂O₄. The surface roughness of AlN is mainly determined by the extent of the lattice mismatch. It has been also found that the roughness at the hetero-interface between GaN and AlN formed by PLD coincides with the surface roughness of the AlN layer.     

Nonpolar a-plane GaN grown on r-plane sapphire using multilayer AlN buffer by metalorganic chemical vapor deposition

Mirror-like and pit-free non-polar a-plane (1 1 −2 0) GaN films are grown on r-plane (1 −1 0 2) sapphire substrates using metalorganic chemical vapor deposition (MOCVD) with multilayer high-low-high temperature AlN buffer layers. The buffer layer structure and film quality are essential to the growth of a flat, crack-free and pit-free a-plane GaN film. The multilayer AlN buffer structure includes a thin low-temperature-deposited AlN (LT-AlN) layer inserted into the high-temperature-deposited AlN (HT-AlN) layer. The results demonstrate that the multilayer AlN buffer structure can improve the surface morphology of the upper a-plane GaN film. The grown multilayer AlN buffer structure reduced the tensile stress on the AlN buffer layers and increased the compressive stress on the a-plane GaN film. The multilayer AlN buffer structure markedly improves the surface morphology of the a-plane GaN film, as revealed by scanning electron microscopy. The effects of various growth V/III ratios was investigated to obtain a-plane GaN films with better surface morphology. The mean roughness of the surface was 1.02 nm, as revealed by atomic force microscopy. Accordingly, the multilayer AlN buffer structure improves the surface morphology and facilitates the complete coalescence of the a-plane GaN layer.     

PEALD-deposited crystalline GaN films on Si(100) substrates with sharp interfaces

Polycrystalline gallium nitride(GaN) thin films were deposited on Si(100) substrates via plasma-enhanced atomic layer deposition(PEALD) under optimal deposition parameters. In this work, we focus on the research of the GaN/Si(100)interfacial properties. The x-ray reflectivity measurements show the clearly-resolved fringes for all the as-grown GaN films, which reveals a perfectly smooth interface between the GaN film and Si(100), and this feature of sharp interface is further confirmed by high resolution transmission electron microscopy(HRTEM). However, an amorphous interfacial layer(~ 2 nm) can be observed from the HRTEM images, and is determined to be mixture of Ga_xO_y and GaN by xray photoelectron spectroscopy. To investigate the effect of this interlayer on the GaN growth, an AlN buffer layer was employed for GaN deposition. No interlayer is observed between GaN and AlN, and GaN shows better crystallization and lower oxygen impurity during the initial growth stage than the GaN with an interlayer.     

Effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition

The effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence(PL) with the excitation wavelength as short as ～ 177 nm. Annealing experiments were carried out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200℃ to 1600℃. It is found that surface roughness reduced and compressive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties,a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL–ONcomplex in the AlN material.     

The dispersion properties of surface acoustic wave devices on AlN/LiNbO3 film/substrate structure

Highly c-axis oriented aluminum nitride (AlN) films were deposited on z-cut LiNbO₃ substrates by reactive rf magnetron sputtering. The crystalline properties investigated by X-ray diffraction (XRD) revealed that AlN film with (0 0 2) preferred orientation was improved by an increase of the deposition time within the experimental range. However, the surface morphology of AlN film measured by scanning probe microscopy (SPM) showed that the roughness was getting worse with increase of deposition time. Surface acoustic wave (SAW) properties, measured by a network analyzer in the structure consisting of highly c-axis AlN films on z-cut LiNbO₃ substrates, were investigated. The phase velocity (V_P) was significantly increased by the increase of h/λ, where h is the thickness of AlN film and λ is the wavelength. However, the insertion loss (IL) of SAW filters was also increased by the increase of h/λ. Experimental results on the temperature characteristics of SAW devices are also presented.     

Mechanical and physicochemical properties of AlN thin films obtained by pulsed laser deposition

AlN thin films have been deposited on Si(100) substrates by a pulsed laser deposition method. The deposition parameters (pressure, temperature, purity of target) play an important role in the mechanical and physicochemical properties. The films have been characterized using X-ray diffraction, atomic force microscopy, Brillouin light scattering, Fourier transform infrared spectroscopy and wettability testing. With a high purity target of AlN and a temperature deposition of 750 C, the measured Rayleigh wave velocity is close to the one previously determined for AlN films grown at high temperature by metal–organic chemical vapour deposition. Growth of nanocrystalline AlN at low temperature and of AlN film with good crystallinity for samples deposited at higher temperature is confirmed by infrared spectroscopy, as it was by atomic force microscopy, in agreement with X-ray diffraction results. A high hydrophobicity has been measured with zero polar contribution for the surface energy. These results confirm that films made by pulsed laser deposition of pure AlN at relatively low temperature have good prospects for microelectromechanical systems applications.     

Properties of AlN grown by plasma enhanced atomic layer deposition

The influence of growth parameters on the properties of AlN films fabricated by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia precursors was investigated. The atomic concentrations, refractive index, mass density, crystallinity and surface roughness were studied from the films grown in the temperature range of 100-300 °C with plasma discharge times between 2.5 and 30 s. The AlN films were shown to be hydrogen rich having H concentrations in the range of 13-27 at.% with inverse dependence on the growth temperature. The carbon and oxygen concentrations in the films were less than 2.6% and 0.2%, respectively. The refractive index and mass density of the films correlated with the hydrogen concentration so that higher concentrations (lower growth temperatures) resulted in smaller refractive index and mass density. The film grown at 300 °C was found to be crystalline whereas lower growth temperature produced amorphous films.     

Characterization of thick HVPE GaN films

The morphology of the top surface for HVPE GaN layers grown on a MOCVD GaN template with a thin LT-AlN interlayer was investigated. This surface is characterized by the formation of numerous hillocks associated with screw dislocations or nanopipes. Their size is large and may reach more than 1 mm. The rocking curves of the 002 and 102 reflections correspond to a relaxed layer. The HREM images of the as-deposited and annealed interlayers show a perfect atomic structure with a very abrupt AlN/HVPE GaN interface. Thus, the deposition of the LT-AlN layer has promoted the growth of an HVPE layer with an excellent crystalline quality.     

Effect of deposition temperature on the microstructure and surface morphology of c-axis oriented AlN films deposited on sapphire substrate by RF reactive magnetron sputtering

In this paper, c-axis oriented AlN films were prepared on sapphire substrate by RF reactive magnetron sputtering at various deposition temperatures (30–700 °C). The influences of deposition temperature on the chemical composition, crystalline structure and surface morphology of the AlN films were systematically investigated. The as-deposited films were characterized by X-ray photoelectron spectroscopy (XPS), two-dimensional X-ray diffraction (2D-XRD) and atomic force microscopy (AFM). The experimental results show that it can be successfully grown for high-purity and near-stoichiometric (Al/N = 1.12:1) AlN films except for the segregation of a few oxygen impurities exist in the form of Al–O bonding. The chemical composition of as-deposited films is almost independent of substrate temperature in the range of 30–700 °C. However, the crystalline structure and surface morphology of the deposited AlN films are strongly influenced by the deposition temperature. The optimum deposition temperature is 300 °C, giving a good compromise between crystalline structure and surface morphology to grow AlN films.