非晶硅氢合金液晶光阀的研究与发展

本文综述了近四、五年间发展起来的非晶硅(a-Si:H)液晶光阀(LCLV)的研究及进展情况。讨论了以a-Si:H制成光导层或PIN结光二极管形式作光阀的电荷产生层及利用向列型或近晶型液晶作为光调制器(SLM)所组成的液晶光阀的工作原理。分析了a-Si:H本身的性能,光阀上所施加的电压和电压的频率以及采用不同的液晶,组成不同的结构形式等对光阀器件性能的影响。     

液晶光阀阻光层研究

本文研究了阻光层在液晶光阀中的作用，报导了我们首先提出的ｎｃ－Ｓｉ：Ｈ作为液晶光阀阻光层。ａ－Ｓｉ：Ｈ光导层和ｎｃ－Ｓｉ：Ｈ阻光层通过辉光放电等离子体化学气相沉积法连续制得。本文研究了不同沉积条件下ｎｃ－Ｓｉ：Ｈ薄膜结构和光电性质。ａ－Ｓｉ：Ｈ和随这沉积的ｎｃ－Ｓｉ：Ｈ形成了ａ－Ｓｉ：Ｈ／ｎｃ－Ｓｉ：Ｈ异质结。采用ａ－Ｓｉ：Ｈ／ｎｃ－Ｓｉ：Ｈ异质结构液昌光阀可改进器件的许多性能。     

硼轻掺杂对a-Si∶H光电导层性能影响的研究

用等离子体增强化学气相沉积法制备了厚为1μm左右的B轻掺杂a-Si∶H光电导层，得到了a-Si∶H的暗电导率与淀积工艺参数和B掺杂比关系的实验曲线，利用该曲线确定了最佳工艺参数和最佳掺杂比。测量了最佳参数下淀积的a-Si∶H薄膜的电学和光学性能及其受掺杂比的影响。结果表明，当B掺杂比增大时，a-Si∶H的暗电导率先减小后增大，并可发生几个数量级的变化。光电导率减小，折射率略有降低，线性吸收系数显著增大，光学带隙减小。测量的数据表明，我们制备的B轻掺杂a-Si∶H光电导层满足投影机用液晶光阀的要求。     

a—Si／CIS叠层太阳能电池的光诱导性能衰退和稳定性分析

基于pin结构a-Si:H太阳能电池中的空间电荷效应，讨论a-Si/CIS叠层太阳能电池的稳定性。结果表明，光生空穴俘获造成的a-Si:H中正空间电荷密度增加改变了电池内部的电场分布，普遍抬高a-Si:H薄膜中电场强度。在光照射下，空间电荷效应不会给a-Si/CIS叠层结构中的a-Si:H薄膜带来准中性区（低场“死层”），因而没有发生a-Si/CIS叠层太阳能电池顶电池（p-i-n a-Si:H)的光诱导性能衰退，a-Si/CIS叠层结构太阳能电池具有较高的光稳定性。     

光寻址液晶光阀的吸收层

光寻址液晶光阀是一种高分辨率空间光调制器，是高亮度，高分辨率大屏幕光寻址液晶光阀投影机的核心部件，为了避免读出光对图像对比度和分辨率的影响，光阀结构中需要一层高光吸收能力的吸收层。本讨论了光寻址液晶光阀对光吸收层的吸收性能要求，吸收层需求在全光谱范围内都有比较强的吸收，碲化镉薄膜对蓝，绿光有较强的吸收，钒氧配套红光具有较强的吸收，它们具有近似互补的吸收光谱。碲化镉和钒氧酞菁复合多层吸收薄膜综合了两种材料的光吸收特性，在全光谱范围内都有良好的吸收，是一种制作光寻址液晶光阀的吸收层的理想方法。     

硼轻掺杂对a—Si：H光电导层性能影响的研究

用等离子体增强化学气相沉积法制备了厚为1um左右的B轻掺杂a-Si:H光电导层，得到了a-Si:H的暗电导率先减小后增大，并可发生几个数量级的变化，光电导率减小，折射率略有降低，线性吸收系数显增大，光学带隙减小，测量的数据表明，我们制备的B轻掺杂a-Si:H光电导层满足投影机用液晶光阀的要求。     

掺硼非晶硅薄膜的微结构和电学性能研究

以硅烷(SiH4)和硼烷(B2H6)为气相反应先驱体，采用等离子体增强化学气相沉积法，(PECVD)制备出能应用于液晶光阀光导层的硼掺杂非晶氢硅薄膜。X射线衍射、原子力显微镜和光、暗电导测试表明，一定程度的硼掺杂提高了非晶氢硅薄膜的电导率、降低了非晶氢硅薄膜的光、暗电导比；硼掺杂促进薄膜晶态率的增加和硅晶粒尺寸的增大，薄膜的结晶状态将逐渐从非晶硅过渡到纳米硅，最后发展为多晶硅。红外吸收谱研究表明了大量的硼原子与硅、氢原子之间能形成某些形式的复合体，仅有少量硼元素对受主掺杂有贡献。     

紫外透射型液晶光阈用ZnSxSe1—x薄膜的研究

描述了透射型ZnSxSe1-x光盲紫外液晶光阀的结构和工作原理，并从器件的电学模型出发，着重讨论了整体器件对ZnSxSe1-x光敏层的特殊要求，采用分子束外延技术在ITO石英导电玻璃上制备了不同组分的三元ZnSxSe1-x多晶薄膜，通过控制反应时的生长参数，制备出了符合器件设计要求的光敏层薄膜，室温下，薄膜的紫外／可见光响应对比度大于10^3，响应波长截止边河可通过控制薄膜中的Se组分，在360－410nm范围内连续可调，薄膜的紫外／可见光吸收系数比大于10^3，在液晶光阀工作的低频段（＜200Hz)，其暗阻抗在10^5-10^6Ωcm^2之间；暗／亮阻抗比满足器件要求。     

液晶光阀中的α-Si:H光导膜研究

本文对在光学信息处理中应用的液晶光阀的关键性膜层——光电导膜采用新近开发的非晶硅材料作了一些探索。研究表明,响应快速的α-Si:H薄膜用于液晶光阀是很有前途的。     

酞菁氧钛／氯丹蓝偶氮单层复合半导体的制备与光导性能

本论文报道了酞菁氧钛／氯丹蓝偶氮单层复合光导体的制备方法，探讨了溶剂、光生材料与传输材料的配比等条件对光导性能的影响。光导性能测试结果表明，复合单层光导体比单一材料的单层光导体光导性能有明显提高，在可见光区和近红外区都表现出很高的光敏性，具有光导性能互补效应。     

nc-Si:H薄膜的内应力特性研究

测试了采用PECVD生长的氢化纳米硅(nc-Si：H)薄膜的内应力。利用XRD、Raman、AFM、HRTEM研究了nc-Si：H薄膜的微结构，用全场薄膜应力测试仪测量了nc-Si：H薄膜的内应力。结果表明：nc-Si：H薄膜的内应力与薄膜的微结构密切相关，强烈依赖于制备工艺。压应力随掺杂浓度的提高而增加；在一定功率密度范围内掺磷nc-Si：H薄膜的压应力随功率密度增加而减少，并过渡为张应力；在373-523K之间，掺硼nc-si：H薄膜的压应力随衬底温度升高而增加；nc-Si：H薄膜的压应力随氢气对硅烷稀释比的变化而变化。     

Structural changes in tungsten wire and their effect on the properties of hydrogenated nanocrystalline cubic silicon carbide thin films

We investigated the structural changes in tungsten wire heated to 1800 °C in SiH₄/CH₄/H₂/N₂ atmosphere and the effect of the aging tungsten wire on the properties of N-doped hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) thin films. The aged tungsten wire had two parts: hot parts of the middle of the wire and relatively cold parts connected to clamps. Tungsten carbide (W₂C) layer formed in the wire of the hot parts, while crystalline silicon and cubic silicon carbide (c-Si/3C-SiC) layer deposited on the wire of the cold parts. N-doped nc-3C-SiC:H thin films were deposited for 5 min (thickness: ~ 30 nm) after the tungsten wire was heated under the same condition as during the film deposition for given times (exposure time). No changes in the structural, electrical and optical properties of the nc-3C-SiC:H thin films were observed for the exposure time up to 450 min.     

Black phosphorus induced photo-doping for high-performance organic-silicon heterojunction photovoltaics

In conventional crystalline silicon (Si) homojunction solar cells,a strategy of doping by transporting phosphorus or boron impurities into Si is commonly used to build Ohmic contacts at rear electrodes.However,this technique involves an energy intensive,high temperature (～ 800 ℃) process and toxic doping materials.Black phosphorus (BP) is a two-dimensional,narrow bandgap semiconductor with high carrier mobility that exhibits broad light harvesting properties.Here,we place BP:zinc oxide (ZnO) composite films between Si and aluminum (Al) to improve their contact.Once the BP harvests photons with energies below 1.1 eV from the crystalline Si,the ZnO carrier concentration increases dramatically due to charge injection.This photo-induced doping results in a high carrier concentration in the ZnO film,mimicking the modulated doping technique used in semiconductor heterojunctions.We show that photo-induced carriers dramatically increase the conductivities of the BP-modified ZnO films,thus reducing the contact resistance between Si and Al.A photovoltaic power conversion efficiency of 15.2％ is achieved in organic-Si heterojunction solar cells that use a ZnO:BP layer.These findings demonstrate an effective way of improving Si/metal contact via a simple,low temperature process.     

Defects in amorphous and solid phase epitaxial silicon

The microstructural morphology of amorphous Si (a-Si) layers deposited in ultrahigh vacuum, as well as crystalline Si grown by solid phase epitaxy (SPE), was studied as a function of Al doping and vapour beam incidence angle. The microstructure of the films was investigated using cross-section transmission electron microscopy. All a-Si layers have a columnar structure, with an average column width of 5 nm. The direction of the columns abruptly changes with the change of deposition direction and shows local column tilts and void formation at substrate surface irregularities. These built-in defects in the a-Si films also influence the defect structure in epitaxial Si films grown by SPE. Voids are initially aligned along the column directions and extra voids form owing to irregularities of the columnar structure. Doping of amorphous Si with Al to 10¹⁸−10²⁰ cm⁻³ does not leave detectable effects in the amorphous structure itself, but will increase the void density of the re-grown SPE Si layers. Furthermore, segregation of Al resulting in metallic inclusions in the amorphous crystalline interface causes metal induced crystallization of Si at temperatures far below the normal SPE regrowth temperature, thus preventing the formation of single crystalline silicon in a single-step process.     

RF sputtered piezoelectric zinc oxide thin film for transducer applications

This paper demonstrates the substrate dependency of the c-axis zinc oxide growth in radio-frequency sputtering system. Different deposition conditions were designed to study the influences of Si, SiO₂/Si, Au/Ti/Si, and Au/Ti/SiO₂/Si substrates on the piezoelectric and crystalline qualities of the ZnO thin films. Experimental results showed that the multilayer of Au/Ti/SiO₂/Si-coated silicon substrate provided a surface that facilitated the growth of ZnO thin film with the most preferred crystalline orientation. The 1.5 μm-thick thermally grown amorphous silicon dioxide layer effectively masked the crystalline surface of the silicon substrate, thus allowing the depositions of high-quality 20 nm-thick titanium adhesion layer followed by 150 nm-thick of gold thin film. The gold-coated surface allowed deposition of highly columnar ZnO polycrystalline structures. It was also demonstrated that by lowering the deposition rate at the start of sputtering by lowering RF power to less than one-third of the targeted RF power, a fine ZnO seed layer could be created for subsequent higher-rate deposition. This two-step deposition method resulted in substantially enhanced ZnO film quality compared to single-step approach. The influence of stress relaxation by annealing was also investigated and was found to be effective in releasing most of the residual stress in this layered structure.     

Microstructures of microcrystalline silicon thin films prepared by hot wire chemical vapor deposition

Undoped hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared at low temperature by hot wire chemical vapor deposition (HWCVD). Microstructures of the μc-Si:H films with different H₂/SiH₄ ratios and deposition pressures have been characterized by infrared spectroscopy X-ray diffraction (XRD), Raman scattering, Fourier transform (FTIR), cross-sectional transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The crystallization of silicon thin film was enhanced by hydrogen dilution and deposition pressure. The TEM result shows the columnar growth of μc-Si:H thin films. An initial microcrystalline Si layer on the glass substrate, instead of the amorphous layer commonly observed in plasma enhanced chemical vapor deposition (PECVD), was observed from TEM and backside incident Raman spectra. The SAXS data indicate an enhancement of the mass density of μc-Si:H films by hydrogen dilution. Finally, combining the FTIR data with the SAXS experiment suggests that the Si---H bonds in μc-Si:H and in polycrystalline Si thin films are located at the grain boundaries.     

In-situ dilatometric study of Metal/Si multilayer film electrodes

Silicon film and Metal/Si multilayer films of three different metals, Ti, Al and Zn, were prepared via magnetron sputtering. The electrochemical performance of these films was investigated, with a focus on the Li⁺ intercalation behaviour, using Auger electron spectroscopy and in-situ electrochemical dilatometry. Comparative studies of silicon film electrodes and Metal/Si multilayer film electrodes were also made. The results of in-situ electrochemical dilatometry indicate that Metal/Si multilayer film electrodes expand significantly less than silicon film electrodes when a similar amount of lithium ions are intercalated. Among films with a similar, sandwich-like structure, Ti/Si films exhibit the least volume expansion; whereas those composed of Al/Si films expand the most. Moreover, the expansion rates of multilayer film electrodes are slower than silicon film electrodes.     

Al预沉积层对金属有机物化学气相沉积方法在Si衬底上生长AlN缓冲层和GaN外延层的影响

采用金属有机物化学气相沉积法(MOCVD)在硅(Si)衬底制备铝/氮化铝/氮化镓(Al/AlN/GaN)多层薄膜,使用光学显微镜(OM)、原子力显微镜(AFM)、X射线衍射(XRD)等手段表征AlN和GaN薄膜的微观结构和晶体质量,研究了TMAl流量对AlN薄膜和GaN薄膜的形核和生长机制的影响。结果表明,预沉积Al层能促进AlN的形核和生长,进而提高GaN外延层的薄膜质量。TMAl流量太低则预沉积Al层不充分,AlN缓冲层的质量取决于由形核长大的高结晶度AlN薄膜与在气氛中团聚长大并沉积的低结晶度AlN薄膜之间的竞争,AlN薄膜的质量随着TMAl流量的升高而提高,GaN薄膜的质量也随之提高。TMAl流量太高则预沉积Al层过厚,AlN缓冲层的质量取决于由形核长大的高结晶度AlN薄膜与Al-Si回融蚀刻之间的竞争,AlN薄膜的质量随着TMAl流量的升高而降低,GaN薄膜的质量也随之降低。     

Electron microscopic characterization of reactively sputtered ZnO films with different Al-doping levels

Highly conductive and transparent ZnO:Al films for solar cell applications were deposited by reactive co-sputtering of Zn and Al from separate targets onto silicon substrates. The structure of the films was characterized with FE-SEM and HREM. Films with Al-doping levels up to 5 at.% show a columnar structure. The columnar grains are mainly composed of ZnO in the hexagonal wurtzite structure. The single grains consist of mutually tilted parts. Stacking faults and twins were observed. Al influences the growth of nuclei of columnar grains. Near the interface nanocrystallites of different phases were discovered. At the ZnO/Si interface an amorphous silicon oxide layer was formed. The nanocrystalline region grows with increasing Al-doping level. Above an Al concentration of 5 at.% the films exhibit a nanocrystalline structure.