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。     

工艺条件对硼掺杂纳米硅薄膜微结构及力学性能的影响

采用射频和直流偏压(RF+DC)双重激励源,在等离子体增强化学气相沉积(PECVD)系统中成功制备了掺硼纳米硅薄膜.改变衬底温度、射频功率和退火温度几个关键工艺参数,利用拉曼(Raman)谱仪、薄膜测厚仪和原子力显微镜(AFM)对掺硼纳米硅薄膜的微结构进行了分析;应用纳米压痕法研究了艺条件对薄膜弹性模量及硬度等力学性能的影响关系.结果表明:薄膜晶态比、平均晶粒大小随着衬底温度的升高均有增大趋势;射频功率对提高薄膜生长速率存在最优值条件;退火对本征和掺硼薄膜表面形貌特征有较大影响,退火后掺硼薄膜表面粗糙度增大明显.薄膜弹性模量及硬度很大程度上受射频功率和后序处理条件的影响,退火使薄膜的力学性能有所提高.针对实验现象,从薄膜结构方面进行了相关的理论阐释.     

射频功率对RF-PECVD法制备纳米硅薄膜结构特征和光学特性的影响

利用射频等离子体增强型化学气相沉积(RF-PECVD)工艺,以SiH4和H2作为反应气体源,在石英衬底上制备了氢化纳米硅(nc-Si∶H)薄膜。其中衬底温度为250℃,H2稀释比为99%,反应压强为133Pa和射频功率为20～60W。采用α-台阶仪、X射线衍射仪(XRD)、Raman光谱仪、傅立叶变换红外光谱仪(FT-IR)和紫外-可见光分光光度计等对薄膜的结构特征和光学特性进行了测试研究。结果表明,随着射频功率的增大,nc-Si∶H薄膜的沉积速率增加,晶化率提高,晶粒尺寸增大和氢含量减小,同时薄膜的吸收系数增强,光学带隙变窄,结构有序性增强和带尾态宽度减小。     

不同衬底制备稀土Nd+3掺杂SnO2薄膜的XRD、SEM分析

采用真空气相沉积法在玻璃和单晶硅衬底[111]上制备纳米SnO2及稀土金属钕掺杂薄膜，并对薄膜进行热处理。对薄膜进行XRD、SEM测试。实验显示，不同衬底制备SnO。薄膜在未掺钕时结构有明显区别，采用同样工艺条件在玻璃衬底上制备的SnO2薄膜没有显示择优生长；在硅衬底上制备未掺钕SnO2薄膜显示出沿[101]晶向择优生长趋势。掺钕（5at％）玻璃衬底制备的薄膜沿[110]衍射峰较强，但薄膜基本呈现自由生长；掺钕后硅衬底制备的薄膜则强烈沿[110]晶向择优生长，随掺钕含量增加择优生长趋势消失，当掺钕含量为（5at％）时薄膜呈自由生长结构较完善。SEM给出在玻璃基片生长的薄膜表面形貌呈均匀小颗粒状，平均晶粒尺寸在30nm左右。硅基片制备的薄膜表面则呈紧密均匀带孔颗粒状；颗粒尺寸约1000nm与计算值相差较大。两种衬底制备的SnO2薄膜经稀土钕掺杂可抑制晶粒生长。本实验中钕掺杂量为5at％（热处理T=500℃，t=45min）时薄膜结构特性最佳。     

硼掺杂对PECVD制备的纳米非晶硅薄膜电学行为的影响

本文采用PECVD法制备硼掺杂纳米非晶硅薄膜(na-Si:H),系统研究了掺杂气体比(B2H6/SiH4)、衬底温度Ts、RF电源功率对薄膜电学性能的影响.研究表明,与传统掺硼非品硅不同,随硼掺杂浓度的增加,掺硼na-Si:H薄膜的电导率先减小后增大并最终趋于饱和,其电导激活能E≈0.50eV、σph/σd＞102,具有应用于太阳能电池p型层的潜力.     

RF溅射稀土（La，Nd）掺杂ZnO薄膜的结构

通过射频磁控溅射技术在Si(111)衬底上制备了未掺杂和镧、钕掺杂ZnO薄膜.XRD分析表明,ZnO薄膜具有c轴择优生长,镧、钕掺杂ZnO薄膜为自由生长的纳米多晶薄膜.用AFM观测薄膜的表面形貌,镧、钕掺杂ZnO薄膜表面形貌粗糙.     

纳米硅薄膜的镜反射红外光谱研究

研究探讨了镜反射红外光谱在纳米材料方面的应用。通过等离子化学气相沉积法(PECVD),制备本征和掺磷的纳米硅薄膜(nc-Si：H),利用镜反射红外光谱研究了本征和掺磷的纳米硅薄膜的光谱特征。通过实验,发现这两种薄膜中都存在多氢键合方式,PECVD工艺参数如衬底温度、直流电压和掺杂浓度对薄膜结构具有一定的影响。     

掺硼纳米非晶硅的太阳能电池窗口层应用研究

本文通过等离子体增强化学气相沉积(PECVD)法沉积p型纳米非晶硅薄膜(na-si:H),系统地研究了掺杂气体比(B2H6/SIH4)、沉积温度、射频电源功率对薄膜结构、光学、电学性能的影响.研究表明,轻掺硼有利于非晶硅薄膜晶化,但随着掺硼量的增加,硼的"毒化"作用又使薄膜变为非晶态;与p型a_si:H相比,掺硼纳米硅薄膜的光学带隙Eopt较高,电导率较高,电导激活能较低,是一种很有潜力的太阳能电池窗口层材料.     

硅纳米晶/SiO2多层薄膜的制备

采用射频磁控溅射结合后续热处理方法制备了镶嵌在SiO2基质中的Si纳米晶（nanocrystalline silicon,nc-Si）薄膜,实验结果表明,在单层nc-Si薄膜中,随着硅含量的增加,Si纳米晶的尺寸、分布密度也增加;在多层nc-Si/SiO2薄膜中,SiO2层会起到限制nc-Si层中Si纳米晶生长的作用,使多层结构中Si纳米晶的尺寸分布更加集中。     

特种化学气相沉积法制备大面积纳米硅薄膜的微结构和电学性能研究

采用可与Si平面工艺兼容的特殊设计的化学气相沉积系统在玻璃衬底上制备了大面积的纳米Si薄膜.高分辨率电子显微镜和选区电子衍射分析表明,成膜温度对薄膜微结构有关键影响,衬底温度的升高促进了薄膜晶态率的提高和Si晶粒的长大.660℃成膜时非晶Si薄膜基体中镶嵌了尺寸为8～12nm,晶态率为50%的纳米Si晶粒,具有明显的纳米Si薄膜微结构特征.用变温薄膜暗电导率测试系统研究表明,随成膜温度的升高,薄膜的晶态率提高、室温暗电导率提高而相应的电导激活能降低,用热激活隧道击穿机制解释了纳米Si薄膜微结构与特殊电学性能的关系.研究了原位后续热处理对薄膜微结构和电学性能的影响,发现延长热处理时间以及采用低温成膜、高温后续退火的热处理方法能有效提高纳米Si薄膜的晶态率,进而提高其室温暗电导率.     

Capacitance analyses of hydrogenated nanocrystalline silicon based thin film transistor

The capacitance-voltage (C-V) measurements within 10⁶-10^− 2 Hz frequency range were performed on the hydrogenated nanocrystalline silicon (nc-Si:H) bottom-gate thin film transistor (TFT) and metal-insulator-amorphous silicon (MIAS) structure, mechanically isolated from the same TFT. It was found that the conducting thin layer in nc-Si:H film expands the effective capacitor area beyond the electrode in the TFT structure, which complicates its C-V curves. Considering the TFT capacitance-frequency (C-F) curves, the equivalent circuit of the TFT structure was proposed and mechanism for this area expansion was discussed. On the other hand, the MIAS C-F curves were fitted by the equivalent circuit models to deduce its electrical properties. nc-Si:H neutral bulk effect was revealed by the dependence of the MIAS capacitance on frequency within 10⁶-10³ Hz at both accumulation and depletion regimes. The inversion in MIAS was detected at 10²-10^− 2 Hz for relatively low negative gate bias without any external activation source. The presence of the ac hopping conductivity in the nc-Si:H film was inferred from the fitting. In addition, the density of the interface traps and its energy distribution were determined.     

Amorphous and nanocrystalline silicon growth on carbon nanotube substrates

In this study, smooth and conformal hydrogenated silicon thin films are examined and analyzed on various multi-walled carbon nanotube (MWCNT) substrates. The films are deposited using radio-frequency plasma-enhanced chemical vapor deposition with He dilution and parameters that are heavily in the γ regime. It is proposed that high-energy plasmas with limited penetration depth can induce crystallization to occur on MWCNT substrates of varying active surface areas. The samples presented exhibit properties that are promising for energy applications, including photovoltaics and lithium-ion batteries and have been studied using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, UV-Vis spectrophotometry, four-point probe measurements, and Fourier transform infrared spectroscopy.     

Preferred growth of nanocrystalline silicon in boron-doped nc-Si:H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2θ≈47° and the exponent of crystalline plane of nc-Si in the film was (2 2 0). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B₂H₆) doping ratio in silane (SiH₄), silane dilution ratio in hydrogen (H₂), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters.     

Structural characterization of boron doped hydrogenated nanocrystalline silicon films

Structural properties of boron doped hydrogenated nanocrystalline silicon films deposited by plasma enhanced chemical vapor deposition method were mainly characterized with Raman and X-ray diffraction methods. The experimental Raman data were fitted better by Fano effect profiles than those by phonon confinement effect line shapes chiefly due to high efficiency doping in grown films. The measured Raman spectra were deconvoluted into three-Gaussian profile components: around the peak positions 520 and 480 cm⁻¹ which contribute from crystalline and amorphous tissues separately, as well as a curve centered at about 500 cm⁻¹, which is attributed to the presence of grain boundaries. The average crystalline grain size and crystalline volume fraction were valued with Raman and X-ray diffraction techniques, respectively, while the error derived from different methods was elucidated. Accordingly, the structural changes including crystallites, grain boundaries and amorphous matrices in doped films with boron doping level were analyzed.     

Preparation and photoluminescence of nanocrystalline Si-rich silicon oxide films by PECVD

Nanocrystalline Si-rich silicon oxide films were deposited using plasma enhanced chemical vapor deposition technique with the mixture of silane (SiH₄), nitrous oxide (N₂O) and hydrogen (H₂) as gas source on quartz glass substrate at the substrate temperature of 300 °C. The effect of the ratio N₂O/SiH₄ on the oxidation, microstructures and photoluminescence (PL) of the as-deposited Si-rich silicon oxide films was investigated with FTIR, XRD and HRTEM. The results reveal that with the increasing ratio of N₂O/SiH₄, more amounts of oxygen are incorporated in the as-deposited films and more nanosized silicon particles are embedded in the films, forming nanocrystalline Si-rich silicon oxide films. The quantum confinement effect or the cooperation of quantum confinement and luminescence center results in the nanocrystalline Si-rich silicon oxide films of higher PL intensity.     

Comparative study of electro-physical properties of heterostructures containing PECVD nanocrystalline and anodic porous silicon layers

We performed a comparative study of the electro-physical properties of heterostructures containing PECVD nanocrystalline silicon (nc-Si) and electro-chemically etched porous silicon (PS) layers over a wide range of thicknesses, in terms of their energy parameters. Based on the proposed analytical expressions and the experimental current-voltage and capacitance-voltage characteristics, we studied the characteristics of the surface states at the nc-Si(or PS) interfaces in Pd-nc-Si(or PS)-p-Si heterostructures. The results revealed that the surface states play an essential role in the carrier transport in both types of heterostructures that were investigated.     

Preparation of ITO thin films applied in nanocrystalline silicon solar cells

ITO thin films were prepared by changing the experimental parameters including gas flow ratio, sputtering pressure and sputtering time in DC magnetron sputtering equipment. The stable experimental parameters of Ar flow at 70 sccm, O₂ flow at 2.5 sccm ∼ 3.0 sccm, sputtering pressure around 0.5 Pa, and sputtering time of 80 s were obtained. Under these parameters, we had achieved the ITO thin films with low resistivity (<4 × 10⁻⁴ Ω ? cm) and high average transmissivity (95.48%, 350 nm ∼ 1100 nm). These ITO thin films were applied in nanocrystalline silicon solar cells as top transparent conductive layer. The solar cell test result showed that the open circuit voltage (Voc) was up to 534.9 mV and the short circuit current density (Jsc) was 21.56 mA/cm².     

氢稀释对纳米晶硅薄膜微结构的影响

采用电感耦合等离子体化学气相沉积技术制备了氮化纳米硅薄膜,利用Raman散射、x射线衍射、红外吸收等技术对不同氮稀释条件下薄膜的微观结构和键合特性变化进行了研究.结果表明,较高的氢稀释比导致薄膜从非晶硅到纳米晶硅的结构转化,随着氮稀释比的增加,所沉积薄膜的晶化度及纳米晶硅的晶粒尺寸单调增加,纳米硅颗粒呈现在(110)方...     

Nanostructure, electrical and optical properties of p-type hydrogenated nanocrystalline silicon films

In this paper, p-type hydrogenated nanocrystalline (nc-Si:H) films were prepared on corning 7059 glass by plasma-enhanced chemical vapor deposition (PECVD) system. The films were deposited with radio frequency (RF) (13.56 MHz) power and direct current (DC) biases stimulation conditions. Borane (B₂H₆) was a doping agent, and the flow ratio η of B₂H₆ component to silane (SiH₄) was varied in the experimental. Films’ surface morphology was investigated with atomic force microscopy (AFM); Raman spectroscopy, X-ray diffraction (XRD) was performed to study the crystalline volume fraction X_c and crystalline size d in films. The electrical and optical properties were gained by Keithly 617 programmable electrometer and ultraviolet-visible (UV-vis) transmission spectra, respectively. It was found that: there are on the film surface many faulty grains, which formed spike-like clusters; increasing the flow ratio η, crystalline volume fraction X_c decreased from 40.4% to 32.0% and crystalline size d decreased from 4.7 to 2.7 nm; the optical band gap E_g^opt increased from 2.16 to 2.4 eV. The electrical properties of p-type nc-Si:H films are affected by annealing treatment and the reaction pressure.     

Hot wire CVD deposition of nanocrystalline silicon solar cells on rough substrates

In silicon thin film solar cell technology, frequently rough or textured substrates are used to scatter the light and enhance its absorption. The important issue of the influence of substrate roughness on silicon nanocrystal growth has been investigated through a series of nc-Si:H single junction p-i-n solar cells containing i-layers deposited with Hot-wire CVD. It is shown that silicon grown on the surface of an unoptimized rough substrate contains structural defects, which deteriorate solar cell performance. By introducing parameter v, voids/substrate area ratio, we could define a criterion for the morphology of light trapping substrates for thin film silicon solar cells: a preferred substrate should have a v value of less than around 1 × 10^- 6, correlated to a substrate surface rms value of lower than around 50 nm. Our Ag/ZnO substrates with rms roughness less than this value typically do not contain microvalleys with opening angles smaller than ~ 110°, resulting in solar cells with improved output performance. We suggest a void-formation model based on selective etching of strained Si-Si atoms due to the collision of growing silicon film surface near the valleys of the substrate.