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Nanoindentation was carried out on thin films of hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapor deposition. The composite values of elastic (Young's) modulus, E c, and hardness, H c, of the film/substrate system were evaluated from the load–displacement curves using the Oliver–Pharr approach. The film-only parameters were obtained employing the extrapolation of the depth profiles of E c and H c. Scanning probe microscopy was employed to image the nanoindenter impressions and to estimate the effect of film roughness and material pile-up on the testing results. It was established that the elastic modulus of thin a-Si:H films is in the range 117–131 GPa, which is lower than for crystalline silicon. In contrast, the values of hardness are in the range 12.2–12.7 GPa, which is comparable to crystalline silicon and higher than for hydrogen-free amorphous silicon. It is suggested that the plastic deformation of a-Si:H proceeds through plastic flow and it is the presence of hydrogen in the amorphous matrix that leads to a higher hardness.  相似文献   

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The kinetics of etching hydrogenated amorphous silicon by a hydrogen plasma has been studied by in-situ spectroscopic ellipsometry measurements. The formation of a hydrogen-rich sublayer is clearly emphasized. Its thickness increases from 7 to 27?nm when the temperature during the hydrogen-plasma treatment is raised from 100 to 250°C. This effect is interpreted by solving the differential equation for trap-limited hydrogen diffusion through a mobile surface. By assigning the thickness of this sublayer to the mean diffusion distance of hydrogen we determined values of the effective diffusion coefficient of hydrogen higher than 10?14?cm2s?1 with an activation energy of 0.22?eV. The density of hydrogen traps is found to decrease from 7.3 × 1018 to 4.5 × 1017?cm?3 as the temperature of the hydrogen treatment increases from 100 to 250°C with an activation energy of 0.43?eV. This effect is interpreted by a thermal equilibrium involving hydrogen transitions between shallow states and hydrogen-trapping sites.  相似文献   

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吴晨阳  谷锦华  冯亚阳  薛源  卢景霄 《物理学报》2012,61(15):157803-157803
本文采用射频等离子体增强化学气相沉积(rf-PECVD)技术在单晶硅衬底上沉积了两个系列的硅薄膜. 通过对样品进行固定角度椭圆偏振测试, 结果表明第一个系列硅薄膜为非晶硅, 形成了突变的a-Si:H/c-Si异质结构, 此结构在HIT电池中有利于形成好的界面特性, 对于非晶硅薄膜采用通常的Tauc-Lorentz摇摆模型(Genosc)拟合结果很好; 第二个系列硅薄膜为外延硅, 对于外延硅薄膜, 随着膜厚增加晶化率降低, 当外延硅薄膜厚度为46 nm时开始非晶硅生长. 对于外延硅通常采用EMA模型(即将硅薄膜体层看成由非晶硅和c-Si构成的混合层)拟合结果较好, 当硅薄膜中出现非晶硅生长时, 将体层分成混合层和非晶硅两层, 采用三层模型拟合结果很好. 本文证实了椭偏光谱分析采用不同的模型可对单晶硅衬底上不同结构的硅薄膜进行有效表征.  相似文献   

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The thermal conductivity of amorphous silicon thin films is measured in one dimension steady state condition. The experimental method is based on heating the sample front surface and monitoring the temperatures at its two sides. The experiments were carried out in conditions ensuring one-direction heat flow from top to bottom throughout the sample thickness. Sputtered a-Si:H films prepared with different conditions are used in order to investigate the dependence of thermal conductivity on material properties (i.e. hydrogen content and microstructure). The results show that, firstly, amorphous silicon is a very bad thermal conductor material. Secondly, the disorder in the film network plays an important role in thermal conduction. The highly disordered film exhibits the lowest thermal conductivity.  相似文献   

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Hydrogenated amorphous silicon surfaces, atomically clean and subsequently oxidized to up to 20 Å oxide thickness, were studied using AES and UPS. The oxidation was made in O2 in the pressure range 10?9 Torr to 5 atm and at 23 and 300°C. The oxidation rate at 23°C was found to be the same as that of crystalline silicon while at 300°C it was appreciably faster. Changes in the d N(E)dE AES Si LVV line shape near 80 eV upon oxidation could be correlated to changes in the silicon-oxygen bonding level observed in UPS. The detailed line shape of the AES Si LVV transition indicates that at 300°C a more homogeneous oxide is produced than at 23°C.  相似文献   

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A direct evidence of substitutional doping in ion beam deposited amorphous hydrogenated silicon by nitrogen is presented. From the analysis of infrared (IR) absorption spectra and Si-2p core level shape, measured with X-ray photoelectron spectroscopy (XPS), the preferential tendency of nitrogen to go in for three-fold coordination at higher concentration and tetrahedral bonding at lower concentration (⩽4 at %) is established. XPS technique has been used for the first time to deduce the upper limit for substitutional solid solubility of the impurity.  相似文献   

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The persistent photoconductivity (PPC) has been observed in undoped, phosphorus-doped, and boron-doped hydrogenated amorphous silicon (a-Si: H) films. As the annealing temperature is raised for these films the decay of residual conductivity is accelerated and the PPC disappears almost completely after annealing at 500°C. These experimental results rule out the mechanism requiring the phosphorus-boron complexes or the deep defects. The PPC is found to be related with the sample inhomogeneity from the experimental observation that the decay of residual conductivity is closely correlated with the microstructure. A model is proposed to explain the PPC in a-Si: H films.  相似文献   

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The extra-mode at 214 cm-1 which is observed in the infrared spectrum of hydrogenated amorphous silicon is interpreted as being due to the presence of small (? 7 atoms) internal surfaces in the samples. Calculations of the phonon density of states at internal surfaces in bulk Si Bethe lattices show a pronounced peak at the edge of the TA band (≈ 210 cm-1. It is shown that when hydrogen is present the mode is infrared active through a dynamical charge transfer mechanism.  相似文献   

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We use the results of time-of-flight experiments in conjunction with recent conclusions about the behavior of the density of localized states below the conduction-band mobility edge to calculate the mobility of electrons moving in extended states in a-Si:H. We find that the extended-state mobility is considerably larger than previous estimates, which were based on the assumption that the exponential behavior responsible for dispersive transport extends all the way to the mobility edge. Using a recent estimate for the density of localized states, we find that the extended state mobility in a-Si:H is about 500 cm2/V-s, a value consistent with the results deduced from high-level injection experiments on p-i-n structures.  相似文献   

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Hydrogenated amorphous silicon exhibits efficient optical transitions across a gap larger than that of crystalline Si. Hydrogen passivates the dangling bonds and endows the material with a reduced number of non-radiative recombination centers. A gap widening has been observed in other hydrogenated semiconductors.Research reported herein was supported by the Department of Energy, Division of Solar Technology, under Contract No. EY-76-C-03-1286 and by RCA Laboratories, Princeton, NJ 08540.  相似文献   

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氢化非晶硅薄膜中氢含量及键合模式的红外分析   总被引:10,自引:0,他引:10       下载免费PDF全文
Fourier红外透射(FTIR)谱技术是研究氢化非晶硅(a-Si∶H)薄膜中氢的含量(CH)及硅—氢键合模式(Si-Hn)最有效的手段.对用等离子体化学气相沉积(PCVD)方法在不同的衬底温度(Ts)下制备出的氢化非晶硅薄膜,通过红外透射光谱的基线拟合、高斯拟合分析,得到了薄膜中的氢含量,硅氢键合模式及其组分,并分析了这些参量随衬底温度变化的规律.  相似文献   

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Ranber Singh  S. Prakash 《Pramana》2003,61(1):121-129
The problem of hydrogen diffusion in hydrogenated amorphous silicon (a-Si:H) is studied semiclassically. It is found that the local hydrogen concentration fluctuations-induced extra potential wells, if intense enough, lead to the localized electronic states in a-Si:H. These localized states are metastable. The trapping of electrons and holes in these states leads to the electrical degradation of the material. These states also act as recombination centers for photo-generated carriers (electrons and holes) which in turn may excite a hydrogen atom from a nearby Si-H bond and breaks the weak (strained) Si-Si bond thereby apparently enhancing the hydrogen diffusion and increasing the light-induced dangling bonds.  相似文献   

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Crystallization of hydrogenated amorphous silicon (a-SI:H) has been initiated using ultrashort laser-pulse train annealing. Optical microscopy, infrared absorption, Raman spectroscopy and photoluminescence measurements show that in our experiment the crystallized layer is localized on the surface and is non-epitaxial. The depth of the crystalline layer and its surface morphology are discussed. A sharp luminescence band at 0.970 eV with fine structure is found after laser annealing and is identified as a recombination center similar to irradiation induced defects in crystalline Si.  相似文献   

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A model of barrier-separated regions is proposed that leads to quantization and spatial correlation of carriers near the band gap of hydrogenated amorphous silicon. The size of these regions, which consist of pure Si bounded by potentials emanating from Si-H bonds, is estimated from a classical percolation picture. Near band gap localized states lie in these quantum well regions and are about 0.3 eV more widely separated than in unbounded Si, thereby accounting for a wide variety of hitherto uncorrelated experimental results. Dopants enhance conductivity by providing conduction paths through the barriers. Spatially coincident pairing of conduction with valence band localized states is speculated to be relevant to other amorphous semiconductors as well.  相似文献   

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Space-charge-limited currents in n+-i-n+ sandwich samples of hydrogenated amorphous silicon have been investigated under alternating current (AC) conditions. When the voltage sweeping rate exceeds the release rate of carriers from deep traps, the AC current-voltage characteristics differ markedly from the direct current (DC) characteristics. This is attributed to the remaining space charge in the samples which acts as a potential barrier and reduces the current. A simple model is proposed to describe the time-dependence of this injection-induced barrier.  相似文献   

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