高温退火对反应溅射制备的a-SiC:H薄膜结构的影响

通过红外透射谱、拉曼散射谱和X射线衍射谱的测量,研究了反应溅射制备的氢化非晶硅碳膜（SP-a-SiC：H）高温退人处理后的结构变化。发现在等时退火的情况下,退火温度对薄膜结构影响明显,H原子的逸出温度与键合有关,H从CH_n中逸出要比从SiH_n键中追出需要更高的温度,样品经800℃退火后,a－SiC：H膜转化为μc－SiC膜     

Infrared absorption of a-SiC : H as a function of the annealing temperature

We performed an investigation on the origin of some temperature-reversible jumps found in the electrical conductivity of a-SiC : H alloys. The samples were grown by plasma-enhanced chemical vapor deposition using a gas mixture of SiH₄+C₂H₂. An infrared (IR) analysis of the variations of the IR absorption peaks was carried out during a thermal cycle: the annealing temperature, T _a, was increased from 25 °C up to 250 °C followed by cooling under identical conditions. The evolution of each IR peak was followed as a function of T _a, acquiring the absorption curve with temperature steps of about 50 °C. The analysis of some characteristic parameters of the IR peaks shows the reversible behavior of the IR absorption as a function of T _a. An attempt is made to correlate the IR absorption peak variations with the discontinuities observed in the electrical conductivity.     

Effect of substrate temperature on HWCVD deposited a-SiC:H film

Hydrogenated amorphous silicon carbon (a-SiC:H) films were deposited using pure SiH₄ and C₂H₂ without hydrogen dilution by hot wire chemical vapor deposition (HWCVD) technique. The photoluminescence, optical, and structural properties of these films were systematically studied as a function of substrate temperature (T_s). a-SiC:H films deposited at lower substrate temperature (T_s) show degradation in their structural, optical and network properties. The hydrogen content (C_H) in the films was found to be increased with decrease of T_s studied. Photoluminescence spectra shift to higher energy and less FWHM at high T_s. Raman spectroscopic analysis showed that structural disorder increases with decrease in the T_s.     

Revisiting the B-factor variation in a-SiC:H deposited by HWCVD

In order to understand material properties in a better way, it is always desirable to come up with new variables that might be related to the film properties. The B-parameter is such a variable, which relates to the quality of a-SiC:H films both in terms of electronic and optical properties. B (scaling factor) is essentially the slope of the straight-line part of the (E)^1/2–E (Tauc plot). Due to dependence on a large number of parameters and no detailed research, many previous authors have surmised that B has an ambiguous correlation with carbon content. We have made an attempt to establish the relation between the B-parameter as a quality-indicating factor of a-SiC:H films in both carbon- and silicon-rich material. For this we studied a-SiC:H films deposited by the HWCVD method with broad deposition parameters of substrate temperature (T_s), filament temperature (T_F) and C₂H₂ fraction. Our results indicate that the B-parameter varies considerably with process conditions such as T_F, total gas pressure and carbon content. An attempt is made to correlate the B-parameter with an opto-electronic parameter, such as the mobility edge, which has relevance to the device-quality aspects of a-SiC:H films prepared by HWCVD.     

渐变组分a-Si∶H/a-SiC∶H膜内部电场的研究

本文报导了渐变组分 a-Si∶H/a-SiC∶H 膜的制备,研究了渐变膜的电学、光学特性,用 EHT 方法对 a-Si∶H 和 a-SiC∶H 的能态密度进行了计算。提出该渐变膜是一种连续变带隙材料,其内部存在自建电场,并从实验上确定了自建电场的方向。     

Comparative study of annealing and oxidation effects in a-SiC:H and a-SiC thin films deposited by radio-frequency magnetron sputtering

Thermal annealing and oxidation effects in hydrogenated (a-SiC:H) and nonhydrogenated (a-SiC) amorphous silicon-carbon alloy films deposited by radio-frequency magnetron sputtering have been studied. The a-SiC:H and a-SiC films were thermally treated in dry Ar, wet Ar, and dry O₂ atmospheres at temperatures up to 1150 °C. The principal effects of thermal annealing in an inert atmosphere on a-SiC:H films were found to be redistribution of hydrogen bonds and formation of amorphous graphitic carbon clusters. Strong oxidation of a-SiC:H was observed after thermal treatment in oxygen at 700 °C while annealing in wet argon caused partial oxidation. Oxidation of the carbon clusters in porous a-SiC:H structures is suggested to be responsible for the higher oxidation efficiency of a-SiC:H in oxygen. In contrast, the structure of a-SiC films remained almost unchanged after annealing in dry argon up to 1000 °C. No oxidation of a-SiC was detected until 1000 °C. Water vapor was found to be more effective at oxidizing a-SiC at 1000 °C than dry oxygen, which is similar to the oxidation behavior of crystalline SiC. The high thermal and oxidation stabilities of a-SiC layers were attributed to the dense and nanovoid-free amorphous SiC network.     

Novel process for low temperature crystallization of a-SiC:H for optoelectronic applications

Metal-induced crystallization (MIC) process was employed to crystallize hydrogenated amorphous silicon carbide (a-SiC:H) films deposited by PECVD on n-type Si substrate. To optimize the crystallization process, Aluminum thin films of different thicknesses were deposited on a-SiC:H films which were then annealed at 600 °C in N₂ environment for 1 h. UV–visible spectrophotometer, atomic force microscopy (AFM) and hall measurement system were used to characterize the films. It was observed from the UV–visible spectrum that the films crystallized using higher Al thickness show absorption in the visible range whereas the samples crystallized with lower Al thickness did not show absorption in the visible range but shows large absorption above the bandgap of the material. Considering UV–visible and Hall measurement data it can be concluded that the sample crystallized with 50 nm of Al can be a good candidate for SiC–Si hetero-junction solar cells.     

Self-biasing effect in colour sensitive photodiodes based on double p-i-n a-SiC:H heterojunctions

A large area colour imager optically addressed is presented. The colour imager consists of a thin wide band gap p-i-n a-SiC:H filtering element deposited on the top of a thick large area a-SiC:H(-p)/a-Si:H(-i)/SiC:H(-n) image sensor, which reveals an intrinsic colour filter. In order to tune the external applied voltage for full colour discrimination, the photocurrent generated by a modulated red light is measured under different optical and electrical bias. Results show that the device, under appropriated readout voltages, behaves itself as an imager and a filter giving information not only on the position where the optical image is absorbed but also on its wavelength and intensity. Identification of the red, green and blue components of the spectrum and simultaneous image recognition were achieved at readout voltages that are able to cancel the self-bias effect due to the different light penetration depth. These voltages shift from positive to negative values as the wavelength of the impinging photons across the back absorber increases. A numerical simulation supports the colour filter analysis.     

Stability and quantum efficiency of a novel type of a-Si:H/a-SiC:H based UV detector

UV detectors based on a-Si:H/a-SiC:H were deposited by plasma enhanced chemical vapor deposition and characterized in terms of their photoelectrical properties. A quantum efficiency of 90%, corresponding to 0.28 A/W, at 365 nm was measured for devices having p-layer and i-layer thickness less than 10 nm. A good uniformity (15%) was achieved on area of 5×5 cm. A linear dependence of the photocurrent as a function of impinging photon flux, corresponding to a constant responsivity, was found. Aging experiments were performed by UV irradiation both on devices and on thin films inserted in the detectors with the aim of investigating the possible correlations.     

Challenges in Fluorescence Detection of Chemical Warfare Agent Vapors Using Solid-State Films

Organophosphorus (OP)-based nerve agents are extremely toxic and potent acetylcholinesterase inhibitors and recent attacks involving nerve agents highlight the need for fast detection and intervention. Fluorescence-based detection, where the sensing material undergoes a chemical reaction with the agent causing a measurable change in the luminescence, is one method for sensing and identifying nerve agents. Most studies use the simulants diethylchlorophosphate and di-iso-propylfluorophosphate to evaluate the performance of sensors due to their reduced toxicity relative to OP nerve agents. While detection of nerve agent simulants in solution is relatively widely reported, there are fewer reports on vapor detection using solid-state sensors. Herein, progress in organic semiconductor sensing materials developed for solid-state detection of OP-based nerve agent vapors is reviewed. The effect of acid impurities arising from the hydrolysis of simulants and nerve agents on the efficacy and selectivity of the reported sensing materials is also discussed. Indeed, in some cases it is unclear whether it is the simulant that is detected or the acid hydrolysis products. Finally, it is highlighted that while analyte diffusion into the sensing film is critical in the design of fast, responsive sensing systems, it is an area that is currently not well studied.     

Detection of change in fluorescence between reactive cyan and the yellow fluorophores using a-SiC:H multilayer transducers

Optical colour sensors based on multilayered a-SiC:H heterostructures can act as voltage controlled optical filters in the visible range. In this article we investigate the application of these structures for Fluorescence Resonance Energy Transfer (FRET) detection, The characteristics of a-SiC:H multilayered structure are studied both theoretically and experimentally in several wavelengths corresponding to different fluorophores. The tunable optical p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures were produced by PECVD and tested for a proper fine tuning in the violet, cyan and yellow wavelengths. The devices were characterized through transmittance and spectral response measurements, under different electrical bias and frequencies. Violet, cyan and yellow signals were applied in simultaneous and results have shown that they can be recovered under suitable applied bias. A theoretical analysis supported by numerical simulation is presented.     

Synthesis of Thin Films with Controlled Absorption Using a Jet High-Frequency Induction Plasmatron

The authors investigate SiO _x and TiO _x (0 < x < 2) thin-film coatings with controlled absorption which are produced using a jet high-frequency plasma under conditions of dynamic vacuum.     

High growth rate of a-SiC:H films using ethane carbon source by HW-CVD method

Hydrogenated amorphous silicon carbide (a-SiC:H) thin films were prepared using pure silane (SiH₄) and ethane (C₂H₆), a novel carbon source, without hydrogen dilution using hot wire chemical vapour deposition (HW-CVD) method at low substrate temperature (200 °C) and at reasonably higher deposition rate (19·5 Å/s < r _d < 3·2 Å/s). Formation of a-SiC:H films has been confirmed from FTIR, Raman and XPS analysis. Influence of deposition pressure on compositional, structural, optical and electrical properties has been investigated. FTIR spectroscopy analysis revealed that there is decrease in C–H and Si–H bond densities while, Si–C bond density increases with increase in deposition pressure. Total hydrogen content drops from 22·6 to 14·4 at.% when deposition pressure is increased. Raman spectra show increase in structural disorder with increase in deposition pressure. It also confirms the formation of nearly stoichiometric a-SiC:H films. Bandgap calculated using both Tauc’s formulation and absorption at 10⁴ cm^?1 shows decreasing trend with increase in deposition pressure. Decrease in refractive index and increase in Urbach energy suggests increase in structural disorder and microvoid density in the films. Finally, it has been concluded that C₂H₆ can be used as an effective carbon source in HW-CVD method to prepare stoichiometric a-SiC:H films.     

Efficiency of Model Induction Motor Using Various Non-Oriented Electrical Steels

1. IntroductionThe total performance of inverter power supplieshas improved drastically as a result of the development of colltrol methods, higher performance in semiconductors, and higher speed, higher integration, andlower cost in integrated circuits, making it possible touse the inverter drive method in a wide range of rotating machinery which requires smaller size and/or variable speed drives. In line with these trends, magneticloss under nonsinusoidal waveform excitation, including lower …     

本征纳米硅薄膜的微结构表征

采用PECVD技术,在玻璃衬底上低温沉积了优质本征纳米硅薄膜,并利用Raman光谱对其微结构作了表征。研究结果表明,硅烷浓度、衬底温度Ts对表征纳米硅薄膜微结构的晶化率和平均晶粒尺寸参数影响很大。SiH4浓度越低,越有利于晶化,对应的晶化率拐点温度越低。平均晶粒尺寸、晶化率随衬底温度的升高具有相似的变化规律,谱中出现的拐点温度一致,暗示它们之间存在紧密的联系。从薄膜生长角度对该实验结果作了合理解释。     

Preliminary results on a-SiC:H based thin film light emitting diode by hot wire CVD

Preliminary results on the first hot wire deposited a-SiC:H based thin film light emitting p–i–n diode having the structure glass/TCO(SnO₂:F)/p-a-SiC:H/i-SiC:H/n-a-SiC:H/Al are reported. The paper discusses the results of our attempts to optimize the p-, i- and the n-layers for the desired electrical and optical properties. The optimized p-layers have a bandgap E_g2 eV and conductivity a little lower than 10⁻⁵ (Ω cm)⁻¹. On the other hand, the optimized n-type a-SiC:H show a conductivity of 10⁻⁴ (Ω cm)⁻¹ with bandgap 2.06 eV. The highest bandgap of the intrinsic layer is approximately 3.4 eV and shows room temperature photoluminescence peak at approximately 2.21 eV. Thin film p–i–n diodes having i-layers with E_g from 2.7 to 3.4 eV show white light emission at room temperature under forward bias of >5 V. However, the 50-nm thick devices show appreciable reverse leakage current and a low emission intensity, which we attribute to the contamination across the p–i interface since these devices are made in a single chamber with the same filament.     

Thermal conductivity and sound velocity measurements of plasma enhanced chemical vapor deposited a-SiC:H thin films

We report ultrafast optical measurements of the thermal conductivity and longitudinal sound velocity for a-SiC:H thin films deposited by plasma enhanced chemical vapor deposition (PECVD). Porous and non-porous films with mass densities ranging from 1.0-2.5 g/cm³ were obtained by intentionally varying the PECVD process conditions. The longitudinal sound velocities for these materials as determined by picosecond ultrasonics ranged from 2370 m/s to 10460 m/s, and the Young's modulus determined from the sound velocity measurements ranged from 5-200 GPa. Time domain thermoreflectance measurements determined the thermal conductivity to range from 0.0009 W/cmK to 0.042 W/cmK.     

a-Si:H薄膜结构对多晶硅薄膜性能的影响

用a一Si:H薄膜经退火晶化成的多晶硅薄膜,其晶化温度、晶粒尺寸和电性能与薄膜的初始结构有密切关系,而a-Si:H薄膜的初始结构依赖于沉积条件.用PCVD方法高速沉积的a-Si:H薄膜,经550℃的低温退火,可以制备平均晶粒尺寸为几百nn,最大晶粒尺寸为2μ,电导率为1.62(Ω·on)-1的优质多晶硅薄膜.     

A Model for the Forward Problem in Magnetic Induction Tomography Using Boundary Integral Equations

We propose a new formulation for the forward problem in magnetic induction tomography (MIT). We formulate the problem in terms of interior and exterior boundary integral equations (BIEs), subject to appropriate boundary conditions. We then transform a standard exterior BIE involving the magnetic vector potential to a BIE involving the electric fields. This transformation eliminates two boundary conditions involving the magnetic vector potential and its normal derivative. This greatly reduces the computational complexity of the model. Here, we compare numerical solutions of the model to analytical solutions.      

PECVD方法直接合成硅氧纳米复合薄膜(nc-SiOx:H)

首次报道了以SiH4、N2O和H2混合气体为原料,用PECVD工艺直接合成硅氧纳米复合薄膜(nc-SiOx:H),未经任何后处理过程观察到了可见光致发光现象,发光峰位于530 nm(2.34eV)左右.通过红外光谱(FTIR)、XRD、高分辨电镜(HRTEM)等手段观察分析了薄膜的组成和结构,薄膜形成了纳米硅在氧化硅网络中的镶嵌式结构.发光强度随薄膜中氧含量的增加而提高,认为薄膜的发光主要是由于跟氧有关的结构缺陷引起的.