用快速光热退火制备多晶硅薄膜的研究

用等离子体增强型化学气相沉积先得到非晶硅(a-Si:H)薄膜,再用卤钨灯照射的方法对其进行快速光热退火(RPTA),得到了多晶硅薄膜.然后,进行XRD衍射谱、暗电导率和拉曼光谱等的测量.结果发现,a-Si:H薄膜在RPTA退火中,退火温度在750℃以上,晶化时间需要2min,退火温度在650℃以下,晶化时间则需要2.5h;晶化后,晶粒的优先取向是(111)晶向;退火温度850℃时,得到的晶粒最大,暗电导率也最大;退火温度越高,晶化程度越好;退火时间越长,晶粒尺寸越大;光子激励在RPTA退火中起着重要作用.     

Epitaxial ZnS/Si core–shell nanowires and single-crystal silicon tube field-effect transistors

Epitaxial single-crystal ZnS/Si core–shell nanowires have been synthesized via a two-step thermal evaporation method. The epitaxial growth is due to the close match of crystal structure between zinc blende ZnS and diamond-like cubic Si. The nanowires have a uniform diameter of 80–200 nm and a length of several to several tens of micrometers. Single-crystal Si nanotubes can be obtained by chemical etching of the ZnS/Si core–shell structure. Characteristics of field-effect transistors (FETs) fabricated from the Si nanotubes suggests that the Si tubes show weak n-type semiconductivity with a mobility of about 3.7×10^?2 cm²/(V s), which is 1 order larger than that of intrinsic Si.     

多晶Si薄膜表面金催化Si纳米线生长

以Au膜作为催化剂和大晶粒多晶Si薄膜为衬底,利用固-液-固生长机制,制备出直径在30～ 100 nm和长度为几百微米的高密度Si纳米线.实验研究了退火温度、生长时间和N2流量对Si纳米线生长的影响.结果表明,随着退火温度的升高,生长时间的延长和N2流量的增加,Si纳米线的长度和密度都显著增加.对不同生长时间下获得的Si纳米线样品进行了X射线衍射测量,结果显示随着生长时间的延长,多晶Si薄膜和表面的Au膜成分都在减少.光致发光谱则显示出弱的蓝光发射和强的红光发射特性,前者应是由非晶SiOx壳层中的氧空位发光中心引起,后者则应归因于Si纳米线芯部与非晶SiOx壳层之间界面区域附近中的Si =O双键态或非桥键氧缺陷中心.     

Low-temperature Si epitaxy on large-grained polycrystalline seed layers by electron–cyclotron resonance chemical vapor deposition

The epitaxial thickening of polycrystalline Si films on glass substrates is of great interest for the realization of crystalline Si thin film solar cells and other large-area thin film devices. In this paper we report on the epitaxial growth of Si at temperatures below on polycrystalline seed layers using electron–cyclotron resonance chemical vapor deposition. The Si seed layers were prepared by aluminum-induced crystallization. The quality of the ECRCVD-grown films strongly depends on the orientation of the underlying seed layer grains. Due to a mainly favorable orientation of the seed layers more than 73% of the substrate area were epitaxially thickened. It turned out that a (1 0 0) preferential orientation is favorable for epitaxial thickening. This, however, is not the only requirement for successful low-temperature epitaxial growth of Si.     

表面补偿的高雾度ZnO∶Al及其在硅薄膜太阳电池中的应用

采用稀盐酸对磁控溅射法制备的平面掺铝氧化锌(ZnO∶Al,AZO)薄膜表面进行湿法刻蚀制绒,分析了盐酸浓度和刻蚀时间对AZO薄膜表面的形貌特征和光电特性的影响。研究发现,湿法刻蚀导致AZO薄膜表面呈现大尺度的陨石坑形貌特征,随刻蚀时间增加,薄膜在大于500 nm的长波范围内光学透过率可维持在70%~75%,且800nm处雾度值可高达48%,陷光能力快速增加,而面电阻率呈现逐渐增加趋势。高的盐酸浓度可以导致薄膜表面呈现较快凹型形貌特征,并可给出较高的雾度值。为了在保持高雾度值的条件下改善薄膜导电性,在2%盐酸刻蚀30 s所制备绒面沉积300 nm AZO薄膜进行厚度补偿,所获得薄膜的表面方块电阻小于10Ω/sq,以其作为前电极所制成的单结薄膜电池转换效率达到9.24%。结果表明,采用酸性刻蚀+厚度补偿方法所制备的绒面AZO薄膜可兼顾高雾度和低电阻的性能要求,是用作硅基薄膜太阳电池前电极的理想材料。     

两步法溅射中缓冲层厚度对Ge薄膜质量的影响

采用低温缓冲层技术制备Ge薄膜,利用AFM和Raman光谱研究缓冲层厚度对低温Ge缓冲层残余应变弛豫的影响.实验结果显示:随着缓冲层厚度的增加,残余应变弛豫度增大.在30 nm厚的低温Ge缓冲层上生长800nm厚的Ge外延层.Ge薄膜具有良好的结晶性,表面粗糙度RMS为2.06 nm.     

Photoluminescence characteristics of Mg- and Si-doped GaN thin films grown by MOCVD technique

We have studied the optical, structural and surface morphology of doped and undoped GaN thin films. The p- and n-type thin films have been successfully prepared by low-pressure MOCVD technique by doping with Mg and Si, respectively. The different carrier concentrations were obtained in the GaN thin films by varying dopant concentrations. Photoluminescence (PL) studies were carried to find the defect levels in the doped and undoped GaN thin films at low temperature. In the undoped GaN thin films, a low intensity and broad yellow band peak was observed. The donor–acceptor pair (DAP) emission and its phonon replicas were observed in both the Si or Mg lightly doped GaN thin films. The dominance of the blue and the yellow emissions increased in the PL spectra, as the carrier concentration was increased. The XRD and SEM analyses were employed to study the structural and surface morphology of the films, respectively. Both the doped and the undoped films exhibited hexagonal structure and polycrystalline nature. Mg-doped GaN thin films showed columnar structure whereas Si-doped films exhibited spherical shape grains.     

Microstructure and optical properties of (Pb,Ca)TiO3 films grown on Si(1 0 0) substrates by a simple sol-gel process

Amorphous and polycrystalline (Pb_0.76Ca_0.24)TiO₃ (PCT) thin films deposited on an Si(1 0 0) substrate have been prepared by a simple sol-gel process. The microstructure and surface morphologies of the thin films have been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The polycrystalline PCT film on the Si(1 0 0) substrate has a tetragonal perovskite structure with grain size from 60 to 110 nm. AFM reveals smooth surfaces and root mean square (rms) roughness of 0.17 and 4.4 nm for amorphous and polycrystalline films, respectively. The refractive index n and extinction coefficient k of the amorphous and polycrystalline thin films was obtained by spectroscopic ellipsometry as a function of the photon energy in the range from 2.0 to 5.4 eV. The maximum n and direct bandgap energies of amorphous and polycrystalline thin films were 2.66 and 4.11 eV, 2.64 and 3.84 eV, respectively.     

Growth and characterization of zirconium oxide thin films on silicon substrate

The growth and characterization of zirconium oxide (ZrO₂) thin films prepared by thermal oxidation of a deposited Zr metal layer on SiO₂/Si were investigated. Uniform ZrO₂ thin film with smooth surface morphology was obtained. The thermal ZrO₂ films showed a polycrystalline structure. The dielectric constant of the ZrO₂ film has been shown to be 23, and the equivalent oxide thickness (EOT) of the ZrO₂ stacked oxide is in the range of 3.38–5.43 nm. MOS capacitors with ZrO₂ dielectric stack show extremely low leakage current density, less than 10^?6 A/cm² at ?4 V. Consequently, using this method, high-quality ZrO₂ films could be fabricated at oxidation temperature as low as 600 °C.     

Effect of Thermal Annealing on Structural Properties,Morphologies and Electrical Properties of TiO2 Thin Films Grown by MOCVD

TiO₂ thin films, were deposited on Si(100) and Si(111) substrates by metalorganic chemical vapor deposition at 500 °C, and have been annealed for 2 min, 30 min and 10 hours at the temperature from 600 °C to 900 °C, in oxygen and air flow, respectively. XRD and atomic force microscopy characterized the structural properties and surface morphologies of the films. As‐deposited films show anatase polycrystalline structure with a surface morphology of regular rectangled grains with distinct boundaries. Rutile phase formed for films annealed above 600 °C, and pure rutile polycrystalline films with (110) orientation can be obtained after annealing under adequate conditions. Rutile annealed films exhibit a surface morphology of equiaxed grains without distinct boundaries. The effects of substrate orientation, annealing time and atmosphere on the structure and surface morphology of films have also been studied. Capacitance‐Voltage measurements have been performed for films deposited on Si(100) before and after annealing. The dielectric properties of TiO₂ films were greatly improved by thermal annealing above 600 °C in oxygen.     

Absorption and emission properties of LBL PPV films deposited on ITO electrodes

In this work we studied the properties of absorption and emission line shape of layer-by-layer (LBL) poly(p-phenylene vinylene) (PPV) on indium-tin oxide (ITO) electrode. To minimize the PPV thermal conversion effects during the polymer processing, we used a less aggressive leaving group in the precursor polymer; minimizing electrode degradation. LBL ITO/PPV films showed the same absorption and emission line shape compared with LBL PPV films deposited on non-metallic substrates (glass). With this analysis we indirectly observe the decrease in the ITO degradation. Atomic force microscopy (AFM) technique was used to analyze quantitatively the microscopic morphology of the film surface. Results indicated that the substrate topology is not affected, to a large extent, by the use of dodecylbenzensulfonate (DBS) ion.     

n型GaAs欧姆接触电极制备工艺

目前,n型GaAs欧姆接触电极的制备方法以蒸镀法为主,然而该方法具有设备价格高、浪费电极材料的缺点。本文采用离子溅射法制备了n型GaAs的欧姆接触电极AuGeNi/Au,通过优化制备过程,可获得表面光滑平整、成分均匀无偏析的电极层。400 ℃氩气气氛下退火处理后,电极与GaAs之间由肖特基接触变为欧姆接触,极间电阻降为原来的1/20。退火温度在400~500 ℃时可得到很小的比接触电阻率(10^-6 Ω·cm²),有利于半导体器件工作稳定性的提高,降低能耗。退火温度低于400 ℃或高于500 ℃后比接触电阻率都较大,这分别与欧姆接触未形成以及Au-Ge合金的“球聚”有关。该制备方法和过程的优点为:设备成本低、流程简便、节省电极材料,具有良好的经济效益和实用价值,适合科研实验室使用。     

Ti/Au复合电极在CdZnTe (111)B面上的表面结构与性能研究

近年来,碲锌镉(CdZnTe)材料制成的探测器已经成为研究热点,适当的接触特性已经成为提高探测器性能的关键问题。本文主要探讨了弱n型CdZnTe晶体(111)B面Ti/Au复合电极的欧姆接触性能,采用两步沉积工艺制备Ti/Au复合电极。通过AFM、FIB/TEM、XPS、I-V等测试方法研究了电极与CdZnTe的界面结构、化学成分和电学性能。结果表明,Ti过渡层的引入可以减轻和改善晶片抛光过程中形成的损伤层,增加了电极与晶体之间的欧姆特性。相比于CdZnTe (111)B面上的Cr/Au复合电极,Ti/Au复合电极的粗糙度更低、接触界面更平整,晶格失配层厚度也更低。Ti中间层促进了金/半界面的互扩散现象, 有利于增加黏附性和降低肖特基势垒,并且在Ti/Au复合电极与CdZnTe接触的界面上没有观察到氧元素的存在。I-V测试表明Ti/Au复合电极具有更加良好的欧姆特性和更低的肖特基势垒。     

Effect of oxygen content on barrier properties of silicon oxide thin film deposited by dual ion-beam sputtering

A silicon oxide thin film barrier was prepared with various oxygen contents and its chemical composition, surface morphology and optical and barrier properties were related to the deposition conditions used. Our study showed that under Ar and O₂ assisted process conditions, a stoichiometric silicon oxide thin film formed at a critical oxygen content during deposition of 40-50%. The thin films deposited at the critical condition showed the lowest surface roughness giving similar or higher optical transmittance than that of the bare polycarbonate (PC) substrate. The boiling and tensile strength test performed on the thin film deposited with assisted ions before the deposition process showed improvement in the adhesion between the oxide layer and the polymer substrate. In addition, interface modification to improve for improving the barrier layer properties of the silicon oxide thin film was achieved through the introduction of dual ion beam sputtering without pre-treatment.     

Ionized-cluster beam epitaxial growth of GaP films on GaP and Si substrates

Epitaxial films of GaP on GaP and Si substrates are grown by the Ionized-Cluster Beam Technology. The doping of Zn and N during the growth of the film are also discussed. A p-type epitaxial film doped by Zn and N shows an absorption spectrum similar to that of a direct transition type semiconductor. P-n junction LEDs are fabricated by depositing p-type GaP on n-type substrate. The luminescence from the device was observed.     

Mixed-phase solidification of thin Si films on SiO2

Mixed-phase solidification (MPS) is a new beam-induced solidification method that can produce large-grained and highly (1 0 0)-surface textured polycrystalline Si films on SiO₂. The grains resulting from this mixed-phase solidification (MPS) method, which was conceived based on a well-known phenomenon of coexisting solid–liquid regions in radiatively melted Si films, are found to be essentially devoid of various intragrain defects that always plague, and subsequently degrade the utility of large-grained Si films previously obtained using other crystallization techniques. It is experimentally shown that multiple exposures are required in order to generate such a polycrystalline microstructure from an initial amorphous precursor. The observed trends are conceptually explained in terms of the melt being initiated primarily at grain boundaries in polycrystalline films, and melting and solidification subsequently proceeding laterally at interface-location specific rates as determined by the local thermodynamic factors, which include the anisotropic surface and interfacial energies of the grains, and the unusual local thermal profile—all transpiring within a near-equilibrium but nonisothermal and dynamic environment that needs to address the thermal and stability requirements associated with the coexisting solid–liquid regions.     

Optimisation of low-temperature silicon epitaxy on seeded glass substrates by ion-assisted deposition

Using single crystalline Si wafer substrates, ion-assisted deposition (IAD) has recently been shown [J. Crystal Growth 268 (2004) 41] to be capable of high-quality high-rate epitaxial Si growth in a non-ultra-high vacuum (non-UHV) environment at low temperatures of about 600 °C. In the present work the non-UHV IAD method is applied to planar borosilicate glass substrates featuring a polycrystalline silicon seed layer and carefully optimised. Using thin-film solar cells as test vehicle, the best trade-off between various contamination-related processes (seed layer surface as well as bulk contamination) is determined. In the optimised IAD process, the temperature of the glass substrate remains below 600 °C. The as-grown Si material is found to respond well to post-growth treatments (rapid thermal annealing, hydrogenation), enabling respectable open-circuit voltages of up to 420 mV under 1-Sun illumination. This proves that the non-UHV IAD method is capable of achieving device-grade polycrystalline silicon material on seeded borosilicate glass substrates.     

High-density silicon and silicon nitride cones

High-density cone-shaped silicon and silicon nitride have been synthesized on Si(1 0 0) substrates via plasma-assisted hot-filament chemical vapor deposition using a gas mixture of nitrogen, hydrogen and methane. Aligned silicon cones containing 3–10 at% C and N have been formed with less than 1 h growth. Further growth can lead to the increase of cone size and density, as well as to the formation of polycrystalline silicon nitride films on the tip and surface. The formation of these materials is thought to be due to the remodification of Si substrates under the effect of plasma and active C and N species. Different nucleation and growth styles were obtained under different growth conditions and reactive gas mixtures.     

CVD金刚石薄膜涂层衬底预处理方法

概述了CVD金刚石薄膜涂层衬底预处理的基本方法,并对一些主要方法作了评述.对于硬质合金类衬底预处理、铜衬底表面预处理、钢铁衬底表面预处理、硅表面预处理,提高膜基结合力的途径除有研磨、超声清洗、植晶、化学腐蚀、等离子体刻蚀、沉积中间过渡层等方法外,还有优化衬底形状、通过表面扩散感应促进成核等手段.     

Light harvesting architectures for electron beam evaporated solid phase crystallized Si thin film solar cells: Statistical and periodic approaches

The fabrication of light trapping architectures for electron beam (e-beam) evaporated polycrystalline Si thin film solar cells is investigated based on tailored self-organized light scattering silica nanospheres and 2 dimensional periodic nanoimprinted structures on glass. A microscopic analysis reveals a unique correlation between the microstructure of high-rate e-beam evaporated Si and the substrate topography. These features provide the basis for the design of nanostructured Si that complies with its distinctive growth characteristics. A layer of self-organized nanospheres embedded in a sol–gel matrix and an anti-reflection coating is found to be an e-beam compatible light trapping approach for poly-Si solar cells, contributing to an increase of 50% in current collection. We developed a preparation process for arrays of equidistant free-standing Si crystals with remarkable optical absorption characteristics based on a nanoimprinted glass substrate by selectively etching e-beam evaporated Si. This periodic approach opens design possibilities for effective three-dimensional architectures for advanced photon management.