Tunable morphological evolution of in situ gold catalysts mediated silicon nanoneedles

Achieving tunable growth of high quality Silicon (Si) nanoneedles (NNs) is challenging. We report the optimized morphology of in situ gold (Au) catalysts assisted SiNNs grown via very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The vapor-liquid-solid (VLS) mechanism mediated morphological evolution is tuned using hydrogen (H₂) and silane (SiH₄) gas flow. Au-coated Si(100) substrates are treated using H₂ plasma to create in situ Au nanoparticles (NPs) with high catalytic activity. FESEM images manifested the existence of mono-dispersed Au NPs and high yield of SiNNs having diameter ranging from 80 to 140 nm and lengths up to 2.31±0.3 µm. Furthermore, these NNs gradually became thinner to form sharp tips of diameter as small as 4 nm. XRD pattern confirmed the diamond (cubic) crystalline phases of SiNNs. HRTEM images revealed the occurrence of Au NPs at the crystalline SiNNs tips. Raman spectrum of as-grown SiNNs exhibited the TO phonon mode accompanied by a red-shift (~23.59 cm⁻¹). Synthesized SiNNs displayed extremely low reflectance (~8%) at short wavelengths (λ<700 nm), indicating excellent antireflection properties. Our controllable and optimized growth method may constitute a basis to achieve high quality SiNN arrays, which are beneficial for various applications.     

VHF-PFLWD法制备μc-SiGe薄膜的研究

分别以Si2 H6和GeH4及SiH4和GeH4两种组合气体为源气体,用甚高频等离子增强化学气相沉积(VHF-PECVD)制备μc-SiGe薄膜.用Raman散射光谱和原子力显微镜(AFM)对薄膜的结构进行研究.结果表明:与SiH4和GeH4制备的薄膜系列相比,Si2H6和GeH4制备的薄膜中Ge的融入速率相对较慢;用...     

VHF-PECVD制备微晶硅材料及电池初步研究

研究了用甚高频等离子体增强化学气相沉积(VHF-PECVD)方法制备的不同沉积气压下的微晶硅薄膜样品。随着沉积气压的逐渐增大,样品的沉积速率也逐渐增大;样品的光敏性和激活能测试结果表明：随气压的变化两者发生了规律性一致的变化;傅立叶变换红外(FTIR)测试表明制备的样品中含有一定量的氧,使得样品呈现弱n型;室温微区喇曼光谱测试分析得到样品的微晶化特征与IR的分析是一致的,用高斯函数对喇曼谱解谱分析定量得出了晶化程度;分析了H处理p／I界面对电池性能的影响;首次在国内用VHF-PECVD制备出效率达4．24％的微晶硅电池。     

硅烷浓度对本征微晶硅材料的影响

利用甚高频等离子体增强化学气相沉积技术沉积微晶硅材料.随硅烷浓度的降低,材料晶化率增加,材料的光学带隙在1.5～1.65eV之间,材料的电导率先增加后减小.采用光发射谱测量技术对辉光进行在线测量,研究沉积条件对VHF等离子体和微晶硅材料特性的影响.实验表明,等离子中的SiH*和H*α对微晶硅材料特性有重要的影响,硅烷浓度为2%～4%时,等离子体中H*α/SiH*的比值处于0.6～0.9,可以得到晶化率在40%～55%的微晶硅材料.     

掺杂室沉积本征微晶硅材料及其在太阳能电池中的应用

在掺杂P室采用甚高频等离子体增强化学气相沉积（VHF—PECVD）技术,制备了不同硅烷浓度条件下的本征微晶硅薄膜．对薄膜电学特性和结构特性的测试结果分析表明：随硅烷浓度的增加,材料的光敏性先略微降低后提高,而晶化率的变化趋势与之相反;X射线衍射（xRD）测试表明材料具有（220）择优晶向．在P腔室中用VHF—PECVD方法制备单结微晶硅太阳能电池的i层和p层,其光电转换效率为4．7％,非晶硅／微晶硅叠层电池（底电池的p层和i层在P室沉积）的效率达8．5％．     

高压高功率VHF-PECVD的微晶硅薄膜高速沉积

采用高压高功率(hphP)甚高频等离子体强强化学气相沉积(VHF-PECVD)法对微晶硅(μc-Si:H)进行高速沉积,在最优沉积条件参数下对hphP和低压低功率(lplP)两组样品沉积速率、光电导、暗电导及光敏性等性能参数进行测试,得到了1.58 nm/s的较高沉积速率、光电性能优秀和更适合薄膜太阳能电池的μc-Si...     

Fabrication of a-SiGeC:H solar cells using monomethyl germane by suppressing carbon incorporation for narrowing optical bandgap

Hydrogenated amorphous silicon-germanium-carbide (a-SiGeC:H) thin films have been fabricated by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) using monomethyl germane (MMG, GeH₃CH₃) as the germanium source. It was found that C incorporation into the films was considerably suppressed under high hydrogen dilution (R_H) and substrate temperature (T_S). Under high R_H and T_S, we were able to narrow the optical band gap (E_opt) of a-SiGeC:H thin films to 1.39 eV, whereas under low R_H and T_S, E_opt increased up to 1.9 eV with increasing MMG. The best electrical properties were obtained for a sample of a-Si_0.68Ge_0.29C_0.03:H, whose E_opt and photosensitivity were 1.58 eV and 10⁵, respectively. When this film was used as an absorber layer in a p-i-n structured solar cell, significant enhancements were observed in its quantum efficiency for long wavelengths.     

Effects of silyl concentration, hydrogen concentration, ion flux, and silyl surface diffusion length on microcrystalline silicon film growth

Two sets of μc-Si: H films as a function of pressure were fabricated by very-high-frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Deposition rate, Raman crystallinity, and photo/dark conductivity were investigated under both low and high power conditions. A plasma fluid model and a surface hydride-dependent precursor diffusion model were constructed to understand the evolution of microcrystalline silicon under low and high power conditions. Silyl, hydrogen, ion flux, silyl surface diffusion length are believed to have much influence on film growth rate, crystallinity and photo electronic properties. But the interesting point is that under a certain condition one or more of these parameters dominate μc-Si: H growth, while other parameters have weak influence. Short-life radicals are found to be the possible major factor on the deterioration of photo sensitivity of μc-Si: H films.     

SUBSTRATE EFFECT ON HYDROGENATED MICROCRYSTALLINE SILICON FILMS DEPOSITED WITH VHF-PECVD TECHNIQUE

Raman spectra and scanning electron microscope （SEM） techniques were used to determine the structural properties of microcrb＇stalline silicon （μc-Si：H） films deposited on different substrates with the very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD） technique. Using the Raman spectra, the values of crystalline volume fraction Xc and average grain size d are 86%, 12.3nm; 65%, 5.45nm; and 38%, 4.05nm, for single crystalline silicon wafer, coming 7059 glass, and general optical glass substrates, respectively. The SEM images further demonstrate the substrate effect on the film surface roughness. For the single crystalline silicon wafer and Coming 7059 glass, the surfaces of the μc-Si：H films are fairly smooth because of the homogenous growth or h＇ttle lattice mismatch. But for general optical glass, the surface of the μ-Si： H film is very rough, thus the growing surface roughness affects the crystallization process and determines the average grain size of the deposited material. Moreover, with the measurements of thickness, photo and dark conductivity, photosensitivity and activation energy, the substrate effect on the deposition rate, optical and electrical properties of the μc-Si：H thin films have also been investigated. On the basis of the above results, it can be concluded that the substrates affect the initial growing layers acting as a seed for the formation of a crystalline-like material and then the deposition rates, optical and electrical properties are also strongly influenced, hence, deposition parameter optimization is the key method that can be used to obtain a good initial growing layer, to realize the deposition of μc-Si：H films with device-grade quality on cheap substrates such as general glass.     

VHF-PECVD法氢化微晶硅薄膜的低温制备

采用VHF-PECVD方法,以高氢稀释的硅烷为反应气体,低温条件下成功地制备了系列μc-Si∶H薄膜.对薄膜的厚度测量表明:增大激发频率和反应气压能有效提高沉积速率;随着等离子体功率密度的增大,沉积速率呈现出先增后减的变化.薄膜的Raman光谱、XRD及TEM等测试结果表明:提高衬底温度或减小硅烷浓度,可增大薄膜的结晶度和平均晶粒尺寸;等离子体激发频率的增大只影响薄膜的结晶度,并使结晶度出现极大值;薄膜中存在 (111)、(220)和(311)三个择优结晶取向,且各结晶取向的平均晶粒尺寸不同.