Morphology, structure, and composition of polycrystalline CdTe films grown on three-dimensional silicon substrates

Polycrystalline CdTe films have been produced on various substrates (glass, ITO-coated glass, sapphire, and microtextured silicon) by quasi-closed space growth, and their structural perfection and surface morphology have been studied by optical microscopy and scanning electron microscopy. Using an energy dispersive X-ray spectrometer and the scanning electron microscope, we have obtained the X-ray emission spectra of the CdTe films and determined their elemental composition. The morphological features of the films have been investigated and the cadmium-to-tellurium atomic ratio in the films has been determined experimentally.     

Growth of CdTe films on Ni-coated microtextured silicon substrates

Based on modeling and calculation results and using appropriate photomasks, we produced microtextured Si substrates, which were then coated with a Ni layer. Next, polycrystalline CdTe films were produced on the Ni by quasi-closed space growth. Their surface morphology was examined by optical microscopy and scanning electron microscopy. We calculated the stress induced in such CdTe/Ni/Si structures by the lattice mismatch and thermal expansion mismatch between the materials in contact.     

Facile fabrication of CdTe/montmorillonite nanocomposite films with stable photoluminescence properties

We report herein the facile synthesis of CdTe/montmorillonite (MMT) nanocomposite films via charge-charge interactions between the CdTe quantum dots (QDs) and MMT platelets. Firstly, negatively charged CdTe QDs were prepared with the use of thioglycolic acid (TGA) as ligand. Then hybrid of the as-prepared TGA-stabilized CdTe QDs with sodium montmorillonite (Na-MMT) and cetyltrimethylammonium-modified montmorillonite (CTA-MMT), respectively, afforded novel CdTe/MMT nanocomposite films. The structure and optical properties of CdTe/MMT nanocomposite films were thoroughly investigated by scanning electron microscope (SEM), ultraviolet transmittance reflection and photoluminescence (PL) measurements. Results showed that CdTe/(CTA-MMT) nanocomposite films exhibited highly enhanced PL intensity compared with CdTe/(Na-MMT) nanocomposite films. More importantly, CdTe QDs in CdTe/(CTA-MMT) nanocomposite films well maintained PL properties even after thermal annealing at 100 °C for 10 h.     

Doping-free fabrication of silicon thin films for schottky solar cell

Thin film Schottky solar cells were fabricated without doping processes, which may provide an alternative approach to the conventional thin film solar cells in the n-i-p configuration. A thin Co layer was coated on a substrate, which worked as a back contact metal and then Si film was grown above it. Deposition condition may modulate the Si film structure to be a fully amorphous Si (a-Si) or a mixing of microcrystalline Si (mc-Si) and a-Si. A thin Au layer was deposited above the grown Si films, which formed a Schottky junction. Two types of Schottky solar cells were prepared on a fully a-Si film and a mixing of mc-Si and a-Si film. Under one sun illumination, the mixing of mc-Si and a-Si device provided 35% and 68.4% enhancement in the open circuit voltage and fill factor compared to that of the amorphous device.     

Facile fabrication of stable superhydrophobic films on aluminum substrates

Compact and uniform layered double hydroxides thin films were fabricated on aluminum substrates using a simple solution-immersion process; upon chemical modification with perfluorosilane, the wettability of the aluminum surface changed from hydrophilic to superhydrophobic. The products were characterized by scanning electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. It is confirmed that the synergic effect of the surface morphology and the surface free energy contribute to this unique surface water repellence. In addition, the superhydrophobic films possess long-term storage stability and good adhesion strength to aluminum substrates, which enhance their potential practical applications.     

Relaxation of extrinsic and intrinsic stresses in germanium substrates with silicon films

Si films were deposited on Ge substrates at 400°C by two different Physical Vapor Deposition techniques: (A) ion beam sputtering and (B) magnetron sputtering. The intrinsic stresses in the as-deposited films were measured to be compressive and much greater in samples (A), about −1500 to −2000 MPa than in samples (B), about −300 to −500 MPa. The substrates were subsequently exposed to thermal treatments for varying times at 800°C. In the lower stressed (B) samples, the films had relaxed and reduced the overall curvature of the structure whereas in the high stresses (A) samples, an irreversible large increase in the substrate curvature was found to occur. This indicated that plastic deformation in the Ge substrates itself had occurred.     

Direct fabrication of metavanadate phosphor films on organic substrates for white-light-emitting devices

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices. Inorganic phosphor films are expected to be applied to these devices because of good chemical stability; however, a substantial reduction of fabrication temperature is required for future industrial uses such as lighting materials fabricated onto flexible organic substrates. Here we show the optical properties of white-light-emitting metavanadate phosphors, AVO3 (A: K, Rb and Cs), and we report a new direct fabrication process for RbVO3 films onto flexible polyethylene terephthalate (PET) substrates by means of a vacuum ultraviolet irradiation using an excimer lamp. In addition, the (Ca,Sr,Pr)TiO3/a-Al2O3/RbVO3/PET heterostructure prepared by an excimer-laser-assisted metal-organic deposition process has demonstrated the possibility of colour modification for RbVO3 films on PET. Our findings suggest new possibilities for further development of large-surface emitting lighting devices.     

High deposition rate processes for the fabrication of microcrystalline silicon thin films

The increase of deposition rate of microcrystalline silicon absorber layers is an essential point for cost reduction in the mass production of thin-film silicon solar cells. In this work we explored a broad range of plasma enhanced chemical vapor deposition (PECVD) parameters in order to increase the deposition rate of intrinsic microcrystalline silicon layers keeping the industrial relevant material quality standards. We combined plasma excitation frequencies in the VHF band with the high pressure high power depletion regime using new deposition facilities and achieved deposition rates as high as 2.8 nm/s. The material quality evaluated from photosensitivity and electron spin resonance measurements is similar to standard microcrystalline silicon deposited at low growth rates. The influence of the deposition power and the deposition pressure on the electrical and structural film properties was investigated.     

Formation and characterization of silicon films on flexible polymer substrates

Polysilicon thin film transistors on flexible substrates are of considerable interest for applications in flexible displays. This paper investigates the formation of nanocrystalline silicon on flexible, transparent polymer substrates. An 800-nm layer of amorphous silicon was deposited on a polyimide substrate followed by a 20-nm layer of aluminum. Samples were rapid thermal annealed at 900 °C for 20 s, forming silicon nanocrystallites in a porous amorphous silicon film. The films were analyzed using Rutherford backscattering spectrometry, Raman Spectroscopy and cross-section transmission electron microscopy. A mechanism is proposed for the formation of silicon nanocrystallites and pores in the a-Si layer.     

Structure of diamond polycrystalline films deposited on silicon substrates

The article presents results of structural studies of polycrystalline diamond thin films deposited by hot filament CVD on silicon substrates. The films were characterized using Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS), Electron Backscattered Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). Both the EBSD patterns and Raman spectra confirm that the grains visible in the electron micrographs are diamond micro-crystallites. The residual stress in the films is found to be in the range between −4.29 GPa and −0.56 GPa depending on the sample thickness. No evidence of lonsdalite and graphite has been registered in the polycrystalline material of the investigated samples. Evidence of the existence of silicon carbide at the diamond/silicon interface is presented. It is also suggested that an amorphous carbonaceous film covers the silicon surface in the regions of holes in the thin diamond layers.     

Si diffusion in magnetron sputtered silicon carbide films deposited on silicon and carbon substrates

Self-diffusion of silicon in magnetron sputtered silicon carbide films deposited on different substrates (crystalline silicon and glassy carbon) is investigated. Since crystallization of amorphous silicon carbide films strongly depends on the substrate, the diffusivity of silicon is expected to depend on the substrate as well. Isotope hetero-structures and secondary ion mass spectrometry were used for analysis. For amorphous samples an upper limit of the diffusivity of 1 × 10^− 21 m²/s is derived at 1100 C°. For crystallized films diffusivities between 1350 °C and 1600 °C are found to be not significantly different for the two types of substrates. For samples deposited on glassy carbon substrates an activation enthalpy ΔH_D = (8.7 ± 0.9) eV was found for the self-diffusion of Si. The consequences of our findings for crystallization are discussed.     

Kinetics and properties of chemically vapour-deposited tungsten films on silicon substrates

The kinetic parameters for the deposition of tungsten films on silicon substrates were evaluated. The reactions (hydrogen reduction or silicon reduction of tungsten hexafluoride) were performed in a resistance-heated horizontal reactor. Film structure and composition were examined by X-ray diffraction, scanning electron microscopy and electron microprobe analysis. The physical, optical, chemical and electrical properties of the films were also measured and are discussed.     

The simultaneous growth of monocrystalline and polycrystalline silicon films with controlled parameters

The influence of the temperature of deposition of nucleation layers on the structure of polycrystalline silicon films which grow locally during the epitaxial growth of monocrystalline films was investigated.The structure of polycrystalline films grown in the high temperature chloride process has been found to depend on the deposition mode of the nucleation layer. For temperature changes in the range 800–860°C, the grain sizes in polycrystalline silicon increase by more than one order of magnitude.It was shown that heat treatment of films of small grain size in an atmosphere of oxygen leads to a decrease in their resistance owing to recrystallization of the grains, whereas during the annealing of films of large grain size the oxidation of intergrain boundaries is the dominant process resulting in an increase in the resistance.The possibility of using polycrystalline films fabricated under specific technological conditions for the isolation of integrated circuit elements was demonstrated.     

Characterization of laser annealed polycrystalline silicon films on various substrates

The structure and property of eximer laser annealed poly-Si films on various substrate materials such as MoW, Cr, were studied. It was found that the crystallinity of the film depended on the recrystallization energy density and substrate materials. The crystallinity of the film on substrate was the highest quality, and the higher the thermal conductivity of the substrate, the poorer the crystallinity of the poly-Si films at the same laser energy density. In the lower laser energy region than optimum, the grain size and surface roughness were increased with increasing laser power due to the increase of the crystallinity and decreased intrinsic stress. On the other hand, in the higher power region than optimum, with the increase of laser power, X-ray intensity and grain size were decreased due to the fast solidification velocity. There was no metal diffusion into poly-Si film but small amount of Si, less than 3 atomic percent, diffused into the metal film during the recrystallization process.     

水热法制备Si基片状ZnO微晶薄膜

采用真空蒸镀法在Si(100)基底上制备了六角片状Zn微晶薄膜,并由N2H4·H2O-水热体系制备了Si基片状ZnO微晶薄膜。XRD、SEM及EDS测试与分析结果表明,纤锌矿结构片状ZnO微晶长度约1μm、厚度约100nm,几乎垂直于Si基面,且在基面上随机组合成连续薄膜。联系室温Si基Zn微晶薄膜氧化物形貌,以"氢氧化锌脱水"反应解释了Si基片状ZnO微晶薄膜的生长机制。光致发光谱测试分析表明,ZnO微晶薄膜有强的近带边紫外光发射和弱的缺陷发射。     

Low temperature fabrication of immersion capacitive micromachined ultrasonic transducers on silicon and dielectric substrates

A maximum processing temperature of 250/spl deg/C is used to fabricate capacitive micromachined ultrasonic transducers (CMUTs) on silicon and quartz substrates for immersion applications. Fabrication on silicon provides a means for electronics integration via post-complementary metal oxide semiconductor (CMOS) processing without sacrificing device performance. Fabrication on quartz reduces parasitic capacitance and allows the use of optical displacement detection methods for CMUTs. The simple, low-temperature process uses metals both as the sacrificial layer for improved dimensional control, and as the bottom electrode for good electrical conductivity and optical reflectivity. This, combined with local sealing of the vacuum cavity by plasma-enhanced chemical-vapor deposition of silicon nitride, provides excellent control of lateral and vertical dimensions of the CMUTs for optimal device performance. In this paper, the fabrication process is described in detail, including process recipes and material characterization results. The CMUTs fabricated for intravascular ultrasound (IVUS) imaging in the 10-20 MHz range and interdigital CMUTs for microfluidic applications in the 5-20 MHz range are presented as device examples. Intra-array and wafer-to-wafer process uniformity is evaluated via electrical impedance measurements on 64-element ring annular IVUS imaging arrays fabricated on silicon and quartz wafers. The resonance frequency in air and collapse voltage variations are measured to be within 1% and 5%, respectively, for both cases. Acoustic pressure and pulse echo measurements also have been performed on 128 /spl mu/m/spl times/32 /spl mu/m IVUS array elements in water, which reveal a performance suitable for forward-looking IVUS imaging at about 16 MHz.     

Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: (1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; (2) Si deposition with remote, linear PECVD; (3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first nip a-Si cells were made on steel substrates with flat barrier layer and had initial efficiencies of 6.3%, showing the potential of the concept.     

硅基三元系PMnN-PZT铁电薄膜制备与研究

利用磁控溅射方法在单晶Si基底上沉积三元系铁电薄膜6%PMnN-94%PZT(6%Pb(Mn1/3,Nb2/3)O3-94%Pb(Zr0.52,Ti0.48)O3),采用淬火方法对薄膜进行处理,以促进薄膜钙钛矿结构形成。同时,在相同条件下制备非掺杂PZT(52/48)薄膜以对比薄膜掺杂效果。运用X射线衍射(XRD)技术分析薄膜晶向及晶体结构,运用Sawyer Tower电路测试薄膜铁电性能,运用激光测振仪测试薄膜的压电系数。实验结果表明,所沉积薄膜为多晶钙钛矿结构铁电薄膜,薄膜铁电剩余极化Pr=23.7μC/cm2,饱和极化Ps=40μC/cm2,矫顽场电压2Ec=139kV/cm,横向压电系数e11=-13.2C/m2,薄膜的铁电及压电性能优良。     

Optical properties of undoped and oxygen doped CuCl films on silicon substrates

Semiconductor photonic emitters operating in the UV range remain an elusive goal. Attention has focused mainly on III-Nitrides. However, a large lattice constant difference between the III-Nitride layers and the compatible substrates results in high densities of misfit dislocations and consequently the device performance is adversely affected. An alternative novel material system, γ-CuCl on silicon, is investigated. Properties of the exciton luminescence from vacuum deposited undoped and oxygen doped CuCl films on Si are studied using temperature dependent photoluminescence spectroscopy. Oxygen doping degrades the optical quality and introduces an intermediate state leading to negative thermal quenching behaviour.     

Optical properties of undoped and oxygen doped CuCl films on silicon substrates

Semiconductor photonic emitters operating in the UV range remain an elusive goal. Attention has focused mainly on III-Nitrides. However, a large lattice constant difference between the III-Nitride layers and the compatible substrates results in high densities of misfit dislocations and consequently the device performance is adversely affected. An alternative novel material system, γ-CuCl on silicon, is investigated. Properties of the exciton luminescence from vacuum deposited undoped and oxygen doped CuCl films on Si are studied using temperature dependent photoluminescence spectroscopy. Oxygen doping degrades the optical quality and introduces an intermediate state leading to negative thermal quenching behaviour.