纳米4-H碳化硅薄膜的掺杂现象

对纳米晶SiC薄膜进行了P和B的掺杂,B掺杂效率比P高,其暗电导预前因子与激活能遵守Meyer-Neldel规则,并有反转Meyer-Neldel规则出现.掺杂效率比非晶态碳化硅薄膜高是纳米碳化硅薄膜的特点之一.非晶态中的隧穿和边界透射对输运有一定贡献.     

Photoconductivity of two-phase hydrogenated silicon films

Electrical, photoelectric, and optical properties of hydrogenated amorphous silicon films with various ratios between the nanocrystalline and amorphous phases in the structure of the material have been studied. On passing from an amorphous to a nanocrystalline structure, the room-temperature conductivity of the films increases by more than five orders of magnitude. With increasing fraction of the nanocrystalline component in the film structure, the steady-state photoconductivity varies nonmonotonically and is determined by the variation in the carrier mobility and lifetime. Introduction of a small fraction of nanocrystals into the amorphous matrix leads to a decrease in the absorption in the defect-related part of the spectrum and, accordingly, to a lower concentration of dangling bonds, which are the main recombination centers in amorphous hydrogenated silicon. At the same time, the photoconductivity in these films becomes lower, which may be due to appearance of new centers that are related to nanocrystals and reduce the lifetime of nonequilibrium carriers.     

基于不同单光子能量拉曼谱的氢化硅薄膜微观特性研究

用等离子体增强化学汽相沉积法（PECVD）在玻璃和单晶硅（c-Si）衬底上分别制备了氢化纳米硅（nc-Si：H）和非晶硅（a-Si：H）薄膜,用紫外、可见和近红外3种不同波长的激光线对不同形态的Si薄膜进行拉曼散射实验研究。研究发现,这些Si薄膜在不同的单光子能量的激光线激发下的拉曼谱线形也不同。进而通过对Si薄膜材料...     

Lifetime of excitons localized in Si nanocrystals in amorphous silicon

The introduction of nanocrystals plays an important role in improving the stability of the amorphous silicon films and increasing the carrier mobility. Here we report results of the study on the photoluminescence and its dynamics in the films of amorphous hydrogenated silicon containing less than 10% of silicon nanocrystals. The comparing of the obtained experimental results with the calculated probability of the resonant tunneling of the excitons localized in silicon nanocrystals is presented. Thus, it has been estimated that the short lifetime of excitons localized in Si nanocrystal is controlled by the resonant tunneling to the nearest tail state of the amorphous matrix.     

Specific features of photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from monosilane–hydrogen mixture

Photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from a monosilane-hydrogen mixture have been studied at a fraction of hydrogen in the mixture that corresponds to the onset of formation of a nanocrystalline phase in the structure of the films obtained. A behavior untypical of amorphous hydrogenated silicon films is observed for the photoconductivity and the spectral dependence of the absorption coefficient. The temperature dependences of the photoconductivity in the films under study are found to vary with the energy of incident photons. At a photon energy of 1.3 eV, temperature quenching of photoconductivity is observed. Prolonged illumination of the films led to a certain decrease in the absorption coefficient at photon energies in the range 1.2–1.5 eV. The results obtained are attributed to the possible presence of silicon nanocrystals in the structure of the films and to the influence of these nanocrystals on their photoelectric and optical properties.     

Crystallization induced by thermal annealing with millisecond pulses in silicon-on-insulator films implanted with high doses of hydrogen ions

The crystallization of silicon-on-insulator films, implanted with high doses of hydrogen ions, upon annealing with millisecond pulses is studied. Immediately after hydrogen-ion implantation, the formation of a three-phase structure composed of silicon nanocrystals, amorphous silicon, and hydrogen bubbles is detected. It is shown that the nanocrystalline structure of the films is retained upon pulsed annealing at temperatures of up to ～1000°C. As the temperature of the millisecond annealing is increased, the nanocrystal dimensions increase from 2 to 5 nm and the fraction of the nanocrystalline phase increases to ～70%. From an analysis of the activation energy of crystal phase growth, it is inferred that the process of the crystallization of silicon films with a high (～50 at %) hydrogen content is limited by atomic-hydrogen diffusion.     

The Preparation of Nanocrystalline Silicon by Plasma-Enhanced Hydrogenation for the Fabrication of Light-Emitting Diodes

The fabrication of nanocrystalline silicon light-emitting diodes is reported using a novel plasma-enhanced hydrogenation method. The fabrication process consisted of the deposition of amorphous silicon on a silicon substrate, a hydrogen plasma treatment, and subsequent annealing, and the deposition of TiO₂, indium-tin oxide, and metal contact layers. The entire process was performed at temperatures below 400 degC and is compatible with standard silicon fabrication technologies. The current-voltage (I-V) characteristics of the device showed a rectifying diode behavior where electrons tunneled through the thin TiO₂ layer and recombined with the holes injected from the P-type silicon substrate leading to photon generation. The structure of the nanocrystalline silicon films was investigated by scanning electron and transmission electron microscopies, and the spectral distribution of the emitted light was measured by a cathodoluminescence     

Effect of the femtosecond laser treatment of hydrogenated amorphous silicon films on their structural, optical, and photoelectric properties

The effect of the femtosecond laser treatment of hydrogenated amorphous silicon (a-Si:H) films on their structural, optical, and photoelectric properties is studied. Under the experimental conditions applied in the study, laser treatment of the film with different radiation intensities induces structural changes that are nonuniform over the film surface. An increase in the radiation intensity yields an increase in the contribution of the nanocrystalline phase to the structure, averaged over the sample surface, as well as an increase in the conductance and photoconductance of the samples. At the same time, for all of the samples, the absorption spectrum obtained by the constant-photocurrent method has a shape typical for those of amorphous silicon. Obtained results indicate the possibility of a-Si:H films photoconductance increase by femtosecond pulse laser treatment.     

纳米硅镶嵌氮化硅薄膜的制备与光致发光特性

为研究氮化硅薄膜发光材料的制备工艺及其光致发光机制,实验采用射频磁控反应溅射技术与热退火处理制备了纳米硅镶嵌氮化硅薄膜材料.利用红外光谱(IR)、X射线衍射谱(XRD)、能谱(EDS)和光致发光谱(PL),对不同工艺条件下薄膜样品的成分、结构和发光特性进行研究,发现在制备的富硅氮化硅薄膜材料中形成了纳米硅颗粒,并计算出其平均尺寸.在510 nm光激发下,观察到纳米硅发光峰,对样品发光机制进行了讨论,认为其较强的发光起因于缺陷态和纳米硅发光.     

Conductivity of thin nanocrystalline silicon films

It is shown in this paper that thin (200–250 Å) hydrogenated nanocrystalline silicon films have low longitudinal conductivity, comparable to that of undoped amorphous silicon, and high transverse conductivity. These films can be used as doping layers in barrier structures with low surface current leakage. It was found that film conductivity decreases by 8–10 orders of magnitude along the layer as the layer thickness is reduced from 1500 to 200 Å. The observed dependence of the conductivity on thickness can be explained (in terms of percolation theory) by destruction of a percolation cluster made up of nanocrystallites as the layer thickness is decreased.     

Mixed phase silicon thin films grown at high rate using 60 MHz assisted VHF-PECVD technique

Mixed phase amorphous and nanocrystalline silicon (a-Si:H and nc-Si:H) thin films were deposited by VHF-PECVD (60 MHz) using Argon (Ar) as the diluent of silane. These amorphous and crystalline silicon thin films were deposited by varying the argon dilution (f_Ar) from 10–97.5% while keeping other process parameters constant. The effects of argon dilution on deposition rate, structural and optical properties of micro/nanocrystalline silicon thin films are studied. It has been observed that the films deposited from f_Ar 10–70% showed the deposition rate >20 Å/s with the highest deposition rate achieved of ~25 Å/s. Structural characterization has been performed by micro-Raman analysis and Atomic force microscopy. Raman shift towards higher wave number (515 cm⁻¹) with increase of f_Ar indicates variation in crystallinity of silicon films. HRTEM studies revealed the distribution of grain size and the degree of crystallinity. Optical absorption spectroscopy confirmed the increase in band gap of the materials from 1.5 to 2.1 eV.     

Low-temperature materials and thin-film transistors for electronics on flexible substrates

The deposition processes and electronic properties of thin-film semiconductors and insulators based on silicon in relation to the fabrication of electronic devices on flexible plastic substrates are considered. The films of amorphous hydrogenated silicon (a-Si:H), nanocrystalline silicon (nc-Si), and amorphous silicon nitride (a-SiN_x), and also thin-film transistors are fabricated at comparatively low temperatures (120°C, 75°C) using existing commercial plasma-chemical equipment. The parameters of thin-film transistors based on a-Si:H and fabricated at the aforementioned relatively low temperatures are compatible with those of high-temperature analogues.     

Nanocrystalline Si:H films made by inductively coupled plasma using internal low inductance antenna

P-type hydrogenated nanocrystalline silicon (nc-Si:H) thin films are prepared on glass substrate by an inductively coupled plasma chemical vapor deposition system using multiple internal low inductance antenna units. The deposition rate as well as the microstructural and electrical properties of the nc-Si:H films are investigated systematically as functions of hydrogen dilution, discharge power and working distance. The effects of various process parameters are identified and rationalized. The applicability of this type of high density plasma to manufacture nc-Si:H films is critically assessed.     

在硅衬底上用HFCVD法生长的纳米SiC薄膜及其室温光致发光

用热丝化学汽相淀积(HFCVD)法在硅衬底上生长具有纳米晶粒结构的碳化硅薄膜.用X射线光电子谱仪(XPS)、X射线衍射(XRD)、傅里叶红外吸收光谱(FTIR)、紫外光Raman散射谱和高分辨透射电子显微镜(HRTEM)对薄膜样品进行了结构和组分分析,并在室温条件下观察到了薄膜的高强度可见光发射.     

Crystallization and Transport Properties of Amorphous Cr-Si Thin Film Thermoelectrics

We studied the thermoelectric properties, crystallization, and stability of amorphous and nanocrystalline states in Cr-Si composite films. Amorphous films, prepared by magnetron sputtering, were transformed into the nanocrystalline state by annealing with in situ thermopower and electrical resistivity measurements. We have found that the amorphous state is stable in these film composites to about 550 K. Prior to crystallization, the amorphous films undergo a structural relaxation, detected by peculiarities in the temperature dependences of the transport properties, but not visible in x-ray or electron diffraction. The magnitude and temperature dependences of electrical conductivity and thermopower indicate that electron transport in the amorphous films is through extended states. The amorphous films are crystallized at annealing temperatures above 550 K into a nanocrystalline composite with an average grain size of 10–20 nm.     

Metal-induced grown Si nanostructures for large-area-device applications

Hydrogenated nanocrystalline silicon (nc-Si:H) films were formed by using a metal (Ni and Co) induced growth (MIG) method, in which nc-Si films epitaxially grow via the formation of a metal disilicide due to an extremely small lattice mismatch. This method avoids high-temperature processing and can be scaled up for large areas. We report on the present state of the fabrication and properties of MIG ne-Si. The effects of processing parameters and different metal prelayers on the Si nanostructures and electrical properties are discussed. The current-voltage-temperature measurement for an Al Schottky diode on MIG nc-Si reveals thermionic field emission to be the dominant carrier transport mechanism in the high-voltage forward current-voltage (I-V) region. The potential applications of these films include large-area solar cells or flat panel displays.     

Optical and electrochemical properties of polyether derivatives of perylenediimides adsorbed on nanocrystalline metal oxide films

We report optical and electrochemical properties of polyether derivatives of perylenediimides (PDIs) thin films formed in various materials (semiconductor, insulator, amorphous and self-assembly). Perylenediimides adsorbed on nanocrystalline TiO₂ (NT) nanocrystalline alumina (NA), amorphous silicon (PS) and neat self-assemblied (SA) films were prepared and characterized based on spectroscopic, electrochemical, spectro-electrochemical techniques. The absorption and fluorescence spectra of PDIs in chloroform exhibit vibronic features. The fluorescence quantum yields (Φ_f) of PDIs with end amino substituents in chloroform solutions are over 0.95, while the quantum yield of triethoxyphenyl substituted PDI Φ_f value is 0.024 in solution. Optical spectroscopy proves that PDIs in metal oxide thin films form aggregated type complexes. An electrochromism, a color change from red to blue/violet, is observed on metal oxide films, that indicates existence of mono and dianion forms of PDIs. Reversibility of electrochemical reductions in NT film depends on the scanning rate. However, electrochromism in NA films is stable and reversibility is independent from scanning rate. Stable mono and diaionic species are formed on NA films. SA films show broad absorption peaks during the voltammetric scan. On the other hand, the first reduction onset potentials of PDIs are almost equal to the onset potential of capacitive current of TiO₂ which lead to low efficiency in dye-sensitized solar cells.     

Evaluation of 1/f Noise Characteristics for Si‐Based Infrared Detection Materials

Silicon antimony films are studied as resistors for uncooled microbolometers. We present the fabrication of silicon films and their alloy films using sputtering and plasma‐enhanced chemical vapor deposition. The sputtered silicon antimony films show a low 1/f noise level compared to plasma‐enhanced chemical vapor deposition (PECVD)‐deposited amorphous silicon due to their very fine nanostructure. Material parameter K is controlled using the sputtering conditions to obtain a low 1/f noise. The calculation for specific detectivity assuming similar properties of silicon antimony and PECVD amorphous silicon shows that silicon antimony film demonstrates an outstanding value compared with PECVD Si film.     

非晶硅薄膜的YAG激光晶化工艺研究

应用YAG激光器在不同工艺条件(激光脉冲频率及脉宽)下对非晶硅薄膜进行了微晶化处理。采用XRD和AFM对所制薄膜的物相结构和表面形貌进行了分析,并探索了激光脉冲占空比对非晶硅薄膜晶化的影响。结果表明,非晶硅薄膜在不同激光脉冲占空比情况下的结晶变化趋势均为多晶硅衬底表层先非晶化,后与非晶硅薄膜一起结晶,而利于其结晶的最佳占空比为1/25。已晶化硅薄膜的晶粒尺寸随占空比的增加先变大后变小。     

甲烷流量对8.5代非晶硅光伏组件P层材料结构和光学性质的影响

本文研究了甲烷流量对作为工业非晶硅光伏组件的p层材料—非晶碳化硅结构和光学性质的影响.p层非晶碳化硅薄膜采用硅烷和甲烷混合气体在射频等离子体增强化学气相沉积(RF-PECVD)设备中沉积制得,该设备是应用材料公司制造的尺寸为2.2 m × 2.6 m的8.5代系统.采用红外光谱和透射/反射谱分析与沉积工艺相关的键结构和光学性质.相同工艺条件下,当甲烷含量从3000 sccm增加到8850 sccm, p层非晶碳化硅薄膜的光学带隙逐步增加. p层非晶碳化硅薄膜的沉积速率随甲烷流量的增加而逐渐减小,其原因是硅烷-甲烷等离子体中SiH3粒子的减少.文中还通过在不同位置取样和分析沉积速率研究了大面积薄膜的均匀性.