Light induced microstructure transformation in a-Si：H films

A series of a-Si:H films are deposited by hot wire assisted microwave electron cyclotron resonant chemical vapour deposition (HW-MWECR-CVD), subsequently exposed under simulated illumination for three hours. This paper studies the microstructure change during illumination by Fourier Transformation Infrared (FTIR) spectra. There are two typical transformation tendencies of microstructure after illumination. It proposes a model of light induced structural change based on the experimental results. It is found that all samples follow the same mechanism during illumination, and intrinsic structure of samples affect the total H content.     

Improvement of total-dose irradiation hardness of silicon-on-insulator materials by modifying the buried oxide layer with ion implantation

The hardening of the buried oxide (BOX) layer of separation by implanted oxygen (SIMOX) silicon-on-insulator (SOI) wafers against total-dose irradiation was investigated by implanting ions into the BOX layers. The tolerance to total-dose irradiation of the BOX layers was characterized by the comparison of the transfer characteristics of SOI NMOS transistors before and after irradiation to a total dose of 2.7 Mrad(SiO₂. The experimental results show that the implantation of silicon ions into the BOX layer can improve the tolerance of the BOX layers to total-dose irradiation. The investigation of the mechanism of the improvement suggests that the deep electron traps introduced by silicon implantation play an important role in the remarkable improvement in radiation hardness of SIMOX SOI wafers.     

An analysis of the incompressible viscous flows problem by meshless method

Generally the incompressible viscous flow problem is described by the Navier--Stokes equation. Based on the weighted residual method the discrete formulation of element-free Galerkin is inferred in this paper. By the step-by-step computation in the field of time, and adopting the least-square estimation of the-same-order shift, this paper has calculated both velocity and pressure from the decoupling independent equations. Each time fraction Newton--Raphson iterative method is applied for the velocity and pressure. Finally, this paper puts the method into practice of the shear-drive cavity flow, verifying the validity, high accuracy and stability.     

The damage of the optical components induced by the stimulated Brillouin scattering

A theory of excitation of ultrasonic waves in the stimulated Brillouin scattering (SBS) process is presented in this paper. By using several reasonable approximations, a numerical calculation of the transient longitudinal SBS shows that large amplitude of acoustic waves can be built up by the nanosecond pulse of high-power laser, which may result in the damage of optical glasses. The maximal density change and the maximal acoustic wave intensity in optical glasses of 5\,cm in thickness are calculated by using different parameters of the high-energy laser, such as the intensity, the pulse width, and the wave length. The damage threshold of the optical glasses is about 80 GW/cm^{2} when using a 1064 nm laser. The dynamic mechanism of SBS is the electrostriction effect of the components coupling with the high-power laser.     

Study on stability of hydrogenated amorphous silicon films

Hydrogenated amorphous silicon （a-Si：H） films with high and same order of magnitude photosensitivity （-10^5） but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content （CH） as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si：H films. We used hydrogen elimination model to explain our experimental results.     

氢化非晶硅薄膜中氢含量及键合模式的红外分析

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.     

Specificities of light-induced relaxation of metastable defects in amorphous hydrogenated silicon

The thermal relaxation kinetics of light-induced metastable defects in a-Si:H was studied prior to and after partial relaxation in the dark and in a dim light. The film lighting was found to change the relaxation rate of the defects and their distribution in relaxation time. This was demonstrated to be due to the concurrent light-induced relaxation and formation of the defects.     

掺溴非晶碳梯度薄膜的制备与分析

采用低压等离子增强化学气相沉积法用溴乙烷、氢气制备了掺溴的非晶碳梯度薄膜。通过样品的XPS能谱分析研究了薄膜沉积速率与氢气流量、溴元素原子分数与溴乙烷流量以及溴元素原子分数与刻蚀时间之间的关系,得出了溴乙烷流量、刻蚀时间对薄膜的主要键态含量、C元素sp2/sp3键态杂化比和薄膜硬度的影响。结果表明：薄膜沉积速率随氢气流量的增加而线性减小,溴元素含量随溴乙烷流量的增加先增加后降低,刻蚀时间越长,溴乙烷流量越小,薄膜越硬     

采用热丝辅助的新型微波电子回旋共振法制备高质量的氢化非晶硅薄膜

采用热丝辅助的新型微波电子回旋共振法制备了高质量的氢化非晶硅薄膜。在制备过程中，热丝对改进薄膜微结构，提高稳定性及光电特性方面起到了重要的作用。实验结果表明：在薄膜的微结构中，硅氢二键含量显著减少并出现了少量微晶相，其有利于改善薄膜的稳定性；在薄膜的光电特性方面，薄膜的沉积速率及光敏性分别达到了2.0nm/s和4.71*105以上。     

Influence of total gas flow rate on microcrystalline silicon films prepared by VHF-PECVD

Hydrogenated microcrystalline silicon (\mu c-Si:H) films are fabricated by very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) at a silane concentration of 7% and a varying total gas flow rate (Hk₂+SiHk₄). Relations between the total gas flow rate and the electrical and structural properties as well as deposition rate of the films are studied. The results indicate that with the total gas flow rate increasing the photosensitivity and deposition rate increase, but the crystalline volume fraction (Xk_c) and dark conductivity decrease. And the intensity of (220) peak first increases then decreases with the increase of the total gas flow rate. The cause for the changes in the structure and deposition rate of the films with the total gas flow rate is investigated using optical emission spectroscopy (OES).     

Influence of heterogeneities on the electronic properties of hydrogenated amorphous silicon

An attempt is made to highlight the importance of inhomogeneities in hydrogenated amorphous silicon (a-Si:H), in controlling its electronic properties. We note that hydrogen increases the gap in a-Si:H and that hydrogen is distributed inhomogeneously in it. This gives rise to long-range potential fluctuations, which are mostly uncorrelated and usually ignored. These and other such considerations have not only enabled us to gain new insights into the behaviour of a-Si:H in general, but have also allowed us to resolve several unsolved puzzles. Among these are questions like why undoped a-Si:H is n-type, why the creation of dangling bonds upon light soaking (LS) so inefficient, why a-Si:H degrades more upon LS when it is doped, why the reciprocity fails for light-induced degradation, why presence of nanocrystalline silicon improves stability and so on. We provide evidence to support some of our ideas and make suggestions for verifying the others.     

非晶硅锗电池性能的调控研究

采用射频等离子体增强化学气相沉积技术, 研究了非晶硅锗薄膜太阳电池. 针对非晶硅锗薄膜材料的本身特性, 通过调控硅锗合金中硅锗的比例, 实现了对硅锗薄膜太阳电池中开路电压和短路电流密度的分别控制. 借助于本征层硅锗材料帯隙梯度的设计, 获得了可有效用于多结叠层电池中的非晶硅锗电池. 关键词： 非晶硅锗薄膜太阳电池 短路电流密度 开路电压 带隙梯度     

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

Hydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of ignition condition on the growth of silicon thin films using plasma enhanced chemical vapour deposition

The influences of the plasma ignition condition in plasma enhanced chemical vapour deposition (PECVD) on the interfaces and the microstructures of hydrogenated microcrystalline Si (μc-Si:H) thin films are investigated.The plasma ignition condition is modified by varying the ratio of SiH 4 to H 2 (R H).For plasma ignited with a constant gas ratio,the time-resolved optical emission spectroscopy presents a low value of the emission intensity ratio of Hα to SiH (I Hα /I SiH) at the initial stage,which leads to a thick amorphous incubation layer.For the ignition condition with a profiling R H,the higher I Hα /I SiH values are realized.By optimizing the R H modulation,a uniform crystallinity along the growth direction and a denser μc-Si:H film can be obtained.However,an excessively high I Hα /I SiH may damage the interface properties,which is indicated by capacitance-voltage (C-V) measurements.Well controlling the ignition condition is critically important for the applications of Si thin films.     

Influence of the deposition parameters on the transition region of hydrogenated silicon films growth

Hydrogenated microcrystalline and amorphous silicon thin films were prepared by very high frequency plasmaenhanced chemical vapour deposition （VHF PECVD） by using a mixture of silane and hydrogen as source gas. The influence of deposition parameters on the transition region of hydrogenated silicon films growth was investigated by varying the silane concentration （SC）, plasma power （Pw）, working pressure （P）, and substrate temperature （Ts）. Results suggest that SC and Ts are the most critical factors that affect the film structure transition from microcrystalline to amorphous phase. A narrow region in the range of SC and Ts, in which the rapid phase transition takes place, was identified. It was found that at lower P or higher Pw, the transition region is shifted to larger SC. In addition, the dark conductivity and photoconductivity decrease with SC and show sharp changes in the transition region. It proposed that the transition process and the transition region are determined by the competition between the etching effect of atomic hydrogen and the growth of amorphous phase.     

Effects of flow ratios on surface morphology and structure of hydrogenated amorphous carbon films prepared by microwave plasma chemical vapor deposition

A series of hydrogenated amorphous carbon (a-C:H) films were deposited on silicon substrates by microwave plasma chemical vapor deposition technique with a mixture of hydrogen and acetylene. The effects of flow ratio of hydrogen to acetylene on surface morphology and structure of a-C:H films were investigated using surface-enhanced Raman spectroscopy and scanning probe microscope (SPM) in the tapping AFM mode. Raman data imply a transition from graphite-like phase to diamond-like bonding configurations when the flow ratio increases. AFM measurements show that the increase in hydrogen content, to some extent, can smoothen the surface morphology and decrease the RMS roughness. Excessive hydrogen is found to cause the formation of polymeric hydrocarbon clusters in the films and reduce deposition rate.     

Effects of gas temperature on optical and transport properties of a-Si:H films deposited by PECVD

Effects of silane temperature (T _g) before glow-discharge on the optical and transport properties of hydrogenated amorphous silicon (a-Si:H) thin films were investigated. The optical measurements show that the refractive index increases with increasing T _g. The transport characterizations show that when T _g increases, the dark conductivity increases. However, the temperature coefficient of resistance decreases. In addition, after holding at 130°C for 20 h, the resistance variation, ΔR/R, of the films deposited at T _g = room temperature (10.8%) is much larger than those deposited at silane temperatures of 80°C (3%) and 160°C (2%). This can be attributed to different rates of defect creation in a-Si:H films caused by various T _g.     

激发频率对高氢稀释下纳米晶硅薄膜生长特性的影响

利用等离子体增强化学气相沉积技术,在高氢稀释条件下,研究不同激发频率对纳米晶硅薄膜生长特性的影响.剖面透射电子显微镜(TEM)分析结果显示,不同激发频率下制备的纳米晶硅薄膜晶化区均呈锥状结构生长,但13.56 MHz激发频率下制备的纳米晶硅薄膜最初生长阶段存在非晶态孵化层,即纳米晶硅薄膜的形成经历了由非晶态孵化层到晶态结构层的转变.而高激发频率(40.68 MHz)下硅纳米晶则能直接在非晶态衬底上生长形成.Raman谱和红外吸收谱测量结果表明高激发频率(40.68 MHz)下制备的纳米晶硅薄膜不但具有较高     

Spectral variations in the optical transition matrix element and their impact on the optical properties associated with hydrogenated amorphous silicon

Using an empirical model for the density of states functions associated with hydrogenated amorphous silicon, in conjunction with an elementary model for the optical transition matrix elements, we aim to explore how variations in the matrix elements impact upon the spectral dependence of the optical properties associated with this material. We also wish to ascertain as to whether or not the hydrogenated amorphous silicon mobility gap result suggested by Jackson et al. [W.B. Jackson, S.M. Kelso, C.C. Tsai, J.W. Allen, S.-J. Oh, Phys. Rev. B 31 (1985) 5187] is consistent with the results of the experiment. We find that the mobility gap value suggested by Jackson et al. is too large. An upper bound on the mobility gap associated with hydrogenated amorphous silicon of 1.68 eV is suggested instead. Electrical measurements performed on undoped hydrogenated amorphous silicon yield a mobility gap value that is consistent with this bound.     

DFT方法研究掺杂氮化硅对SONOS器件保持性能的作用

可通过对氮化硅层掺杂来改变俘获电荷的缺陷种类和数量的方法，改善SONOS非挥发性存储器件的保持性能.建立无定形氮化硅和氧、硫、磷、氟或氯掺杂氮化硅中缺陷的簇模型；根据第一性原理的密度泛函理论(DFT)，对缺陷的簇模型结构优化并计算能量，得到缺陷俘获电荷过程的能量变化.发现缺陷俘获电子的能力比俘获空穴的能力好，电子释放过程应对温度敏感，而空穴释放过程主要由隧穿机理控制.预测与氧氮化硅一样，硫或磷掺杂氮化硅代替氮化硅作为SONOS器件的电荷储存层，可改善器件的保持性能.