Refractive index and thickness analysis of natural silicon dioxide film growing on silicon with variable-angle spectroscopic ellipsometry

The refractive index and thickness of SiO2 thin films naturally grown on Si substrates were determined simultaneously within the wavelength range of 220-1100 nm with variable-angle spectroscopic ellipsometry. Different angles of incidence and wavelength ranges were chosen to enhance the analysis sensitivity for more accurate results. Several optical models describing the practical SiO2-Si system were investigated, and best results were obtained with the optical model, including an interface layer between SiO2 and Si, which proved the existence of the interface layer in this work as described in other publications.

Fractal Pattern Formation In Anodic Bonding Of Pyrex Glass/Al/Si

Anodic bonding of Pyrex glass/Al/Si is an important bonding technique in micro/nanoelectromechanical systems (MEMS/NEMS) industry. The anodic bonding of Pyrex 7740 glass/Aluminum film/Silicon is completed at the temperature from 300 degrees C to 375 degrees C with a bonding voltage between 150 V and 450 V. The fractal patterns are formed in the intermediate Al thin film. This pattern has the fractal dimension of the typical two-dimensional diffusion-limited aggregation (2D DLA) process, and the fractal dimension is around 1.7. The fractal patterns consist of Al and Si crystalline grains, and their occurrences are due to the limited diffusion, aggregation, and crystallization of Si and Al atoms in the intermediate Al layers. The formation of the fractal pattern is helpful to enhance the bonding strength between the Pyrex 7740 glass and the aluminum thin film coated on the crystal silicon substrates.

Super-resolution with a nonlinear thin film: Beam reshaping via internal multi-interference

In laser applications, the size of the focus spot can be reduced beyond the diffraction limit with a thin film of strong nonlinear optical Kerr effect. We present a concise theoretical simulation of the device. The origin of the super-resolution is found to be mainly from the reshaping effect due to the strongly nonlinear refraction mediated multi-interference inside the thin film. In addition, both diffraction and self-focusing effects have been explored and found negligible for highly refractive and ultrathin films in comparison with the reshaping effect. Finally, the theoretic model has been verified in experiments with single Ge2Sb2Te5 film and SiN/Si/SiN/Ge2Sb2Te2 multilayer structures. (c) 2006 American Institute of Physics.

Mo原子溅射能量对Mo／Si薄膜微结构的影响

用磁控溅射法制备了Mo／Si薄膜，用AFM和XRD分别研究了Mo原子的溅射能量不同时，Mo／Si薄膜表面形貌和晶相的变化。通过比较发现，随着Mo原子溅射能量的增大，Mo／Si薄膜表面粗糙度增加，Mo和Si的特征X射线衍射峰也越来越强，并且Mo膜层和Si膜层之间生成了Mo-Si2。Mo原子的溅射能量是诱导非晶Si结晶和MoSi2生成的主要原因。

Laser-induced damage of Ti O2 Si O2 high reflector at 1064 nm

A high laser-induced damage threshold (LIDT) TiO2/SiO2 high reflector (HR) at 1064 nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064 nm with a 12 ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO2 layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR. (C) 2008 American Institute of Physics.

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer

We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

A highly efficient light-trapping structure for thin-film silicon solar cells

A highly efficient light-trapping structure, consisting of a diffractive grating, a distributed Bragg reflector (DBR) and a metal reflector was proposed. As an example, the proposed light-trapping structure with an indium tin oxide (ITO) diffraction grating, an a-Si:H/ITO DBR and an Ag reflector was optimized by the simulation via rigorous coupled-wave analysis (RCWA) for a 2.0-mu m-thick c-Si solar cell with an optimized ITO front antireflection (AR) layer under the air mass 1.5 (AM1.5) solar illumination. The weighted absorptance under the AM1.5 solar spectrum (A(AM1.5)) of the solar cell can reach to 69%, if the DBR is composed of 4 pairs of a-Si:H/ITOs. If the number of a-Si:H/ITO pairs is up to 8, a larger A(AM1.5) of 72% can be obtained. In contrast, if the Ag reflector is not adopted, the combination of the optimized ITO diffraction grating and the 8-pair a-Si:H/ITO DBR can only result in an A(AM1.5) of 68%. As the reference, A(AM1.5) = 31% for the solar cell only with the optimized ITO front AR layer. So, the proposed structure can make the sunlight highly trapped in the solar cell. The adoption of the metal reflector is helpful to obtain highly efficient light-trapping effect with less number of DBR pairs, which makes that such light-trapping structure can be fabricated easily.

Effects of AlGaN/AlN Stacked Interlayers on GaN Growth on Si (111)

We report the growth of high quality and crack-free GaN film on Si (111) substrate using Al0.2Ga0.8N/AlN stacked interlayers. Compared with the previously used single AlN interlayer, the AlGaN/AlN stacked interlayers can more effectively reduce the tensile stress inside the GaN layer. The cross-sectional TEM image reveals the bending and annihilation of threading dislocations (TDs) in the overgrown GaN film which leads to a decrease of TD density.

Role of Bi3+ ions for Er3+ ions efficient 1.54 mu m light emission in Er/Bi codoped SiO2 thin film prepared by sol-gel method

Er/Bi codoped SiO2 thin films were prepared by sol-gel method and spin-on technology with subsequent annealing process. The bismuth silicate crystal phase appeared at low annealing temperature while vanished as annealing temperature exceeded 1000 degrees C, characterized by X-ray diffraction, and Rutherford backscattering measurements well explained the structure change of the films, which was due to the decrease of bismuth concentration. Fine structures of the Er3+-related 1.54 mu m light emission (line width less than 7 nm) at room temperature was observed by photoluminescence (PL) measurement. The PL intensity at 1.54 gm reached maximum at 800 degrees C and decreased dramatically at 1000 degrees C. The PL dependent annealing temperature was studied and suggested a clear link with bismuth silicate phase. Excitation spectrum measurements further reveal the role of Bi3+ ions for Er3+ ions near infrared light emission. Through sol-gel method and thermal treatment, Bi3+ ions can provide a perfect environment for Er3+ ion light emission by forming Er-Bi-Si-O complex. Furthermore, energy transfer from Bi3+ ions to Er3+ ions is evidenced and found to be a more efficient way for Er3+ ions near infrared emission. This makes the Bi3+ ions doped material a promising application for future erbium-doped waveguide amplifier and infrared LED

Preferential orientation growth of AIN thin films on Si (111) substrates by LP-MOCVD

Aluminum nitride (AIN) thin films were deposited on Si (111) substrates by low pressure metalorganic chemical vapor deposition system. The effects of the V/III ratios on the film structure and surface morphology were systematically studied. The chemical states and vibration modes of AIN films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The optical absorption property of the AIN films, characterized by ultraviolet-visible-near infrared spectrophotometer, exhibited a sharp absorption near the wavelength of 206 mm. The AIN (002) preferential orientation growth was obtained at the V/III ratio of 10,000 and the preferential growth mechanism is presented in this paper according to the thermodynamics and kinetics process of the AIN growth.

Surface plasmon enhanced ultraviolet emission from ZnO films deposited on Ag/Si(001) by magnetron sputtering

The ZnO films were grown on Ag/Si(001) substrates by sputtering Ag and ZnO targets successively in a pure Ar ambient. A significant enhancement of ZnO ultraviolet emission and a reduction of its full width of half maximum have been observed while introducing a 100 nm Ag interlayer between ZnO film and Si substrate. Furthermore, a complete suppression of the defect related visible emission was also found for the ZnO/Ag/Si sample. This improved optical performance of ZnO is attributed to the resonant coupling between Ag surface plasmon and ultraviolet emission of ZnO. (c) 2007 American Institute of Physics.

Enhanced charge storage characteristics of silicon nanocrystals fabricated by electron-beam coevaporation of Si and SiOx(x=1 or 2)

In this article, a simple and flexible electron-beam coevaporation (EBCE) technique has been reported of fabrication of the silicon nanocrystals (Si NCs) and their application to the nonvolatile memory. For EBCE, the Si and SiOx(x=1 or 2) were used as source materials. Transmission electron microscopy images and Raman spectra measurement verified the formation of the Si NCs. The average size and area density of the Si NCs can be adjusted by increasing the Si:O weight ratio in source material, which has a great impact on the crystalline volume fraction of the deposited film and on the charge storage characteristics of the Si NCs. A memory window as large as 6.6 V under +/- 8 V sweep voltage was observed for the metal-oxide-semiconductor capacitor structure with the embedded Si NCs.

Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 mum thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1-xN layer at least with 300 nm thickness in the 1 mum thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1-xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously. (C) 2004 American Institute of Physics.

Preparation and characterization of Si sheets by renewed SSP technique

Silicon sheets from powder (SSP) ribbons have been prepared by modified SSP technique using electronic-grade (9N purity) silicon powder. The surface morphology, crystallographic quality, composition and electric properties of the SSP ribbons were investigated by surface profiler, X-ray diffraction (XRD), scanning electron microscopy (SEM), metallurgical microscope, Auger electron spectroscopy (AES) and four-point probe apparatus, respectively. The results show that the SSP ribbon made from electronic-grade silicon powder is a suitable candidate for the substrates of crystalline silicon thin film (CSiTF) solar cells, which could meet the primary requirements of CSiTF solar cell process on the substrates, including surface smoothness, crystallographic quality, purity and electric conductivity, etc. (C) 2004 Elsevier B.V. All rights reserved.

Characterization of polymorphous silicon thin film and solar cells

Polymorphous silicon (pm-Si:H) films have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the pm-Si:H has higher photoconductivity (sigma(ph)), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. There are a blue shift for the stretching mode of IR spectra and a red shift for the wagging mode. The shifts are attributed to the variation of the microstructure. By using pm-Si:H film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100mw/cm(2)) at room temperature (T-R).