In-situ electrical measurement in ion implanted amorphous silicon films

Doping in amorphous silicon has been studied by P, B and Si implantation in evaporated silicon films made by electron beam evaporations. After double implantation of P and B, a compensation effect has been observed in implanted amorphous silicon layer.     

Optical characteristics of implanted silicon films

The first data are presented on the change (following implantation) in the refractive index and the band structure of silicon on sapphire films. The implantation was effected with phosphor ions of 40 keV and doses from 10¹² to 10¹⁶ cm^–2. An increase following implantation of the refractive index and the energy of the first direct allowed transitions E₁ is noted, indicating changes in the second coordination sphere. The profile E₁(x) is studied pointing to heterogenization effects. The films were annealed with ruby laser pulses of 0.2 J/cm². The same laser was used to study the lux dependence of the injection level _n and surface photo-emf V. Hysteresis in the V(_n) dependence (after the use of maximum intensity of the laser beam) is noted indicating irreversible straightening of the bands at the film surface.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 40–43, May, 1984.     

In-depth modifications of implanted amorphous carbon films

Amorphous carbon films (a-C:H) and nitrogen incorporated carbon films [a-C:H(N)] deposited by a self-bias glow discharge have been implanted with 70 keV nitrogen ions at fluences of 0.6, 1 and 2×10¹⁷ N/cm². The in-depth modifications caused by ion implantation were determined by means of nuclear techniques, such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA), as well as by Auger Electron Spectroscopy (AES) and Raman scattering. ERDA profiles show that nitrogen implantation causes hydrogen depletion, the amount of which depends on the film composition and on the ion fluence. In a-C:H(N) films nitrogen loss was also measured. The induced structural modifications in both a-C:H and a-C:H(N) films were followed by both AES, using factor analysis, and microprobe Raman spectroscopy. They turn out to be related to the energy deposited by the incident ions. Our results indicate that the ion-beam bombardment causes in both a-C:H and a-C:H(N) films an increase of either the degree of disorder or the ratio between sp²/sp³ bonds across the hydrogen-depleted layer, which depends on the ion fluence.     

Doping of evaporated amorphous silicon films

It is shown that evaporated amorphous silicon films can be doped interstitially by ion implantation and in-diffusion of lithium. The doping effect is smaller than for glow discharge silicon films, and the doped state is less stable at elevated temperature. This is explained by precipitation as well as out-diffusion effects in connection with the high defect concentration in evaporated films.     

Low energy electron attenuation length studies in thin amorphous carbon films

The results of experiments on low energy electrons passing through thin amorphous carbon films are reported. For electron energies between 50 and 3000 eV, electron attenuation lengths were determined by electron transmission measurements through carbon films of thicknesses between 81 and 210 Å. The density of these amorphous carbon films was also obtained by a sink—float method and found to be 1.90 ± 0.05 g cm^?3. The electron attenuation length for inelastic scattering was found to increase monotonically from approximately 10 to 55 Å over the 50 to 3000 eV range. Over the 500–3000 eV energy region, the results are in good agreement with mean free paths calculated using optically measured dielectric functions.     

Surface smoothening mechanism of amorphous silicon thin films

An important concern in the deposition of thin hydrogenated amorphous silicon () films is to obtain smooth surfaces. Herein, we combine molecular-dynamics simulations with first-principles density functional theory calculations to elucidate the smoothening mechanism of plasma deposited thin films. We show that the deposition precursor may diffuse rapidly on the film surface via overcoordinated surface Si atoms and incorporate into the film preferentially in surface valleys, with activation barriers for incorporation dependent on the local surface morphology. Experimental data on smoothening and precursor diffusion are accounted for.     

Photo-chemical vapor deposition of hydrogenated amorphous silicon films

A photo-chemical vapor deposition, using ultraviolet light excitation and a mercury photo-sensitization, was investigated for depositing hydrogenated amorphous silicon films from SiH₄. The photoelectric and structural properties were examined to characterize the deposited films. Those properties were depended strongly on substrate temperature, and the films which were deposited at a substrate temperature more than 200°C contained dominant SiH configurations. A relatively large single crystalline grain size of about 0.5 m was observed in a 1.0 m thick film, which was obtained at a substrate temperature as low as 200°C. Phosphorus impurity doping into the films and Pt-Schottky diode fabrication were also attempted.     

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.     

Effect of hydrogenation on the electrical conductivity of amorphous silicon carbide

The d.c. conductivity of RF sputtered hydrogenated amorphous SiC films have been studied in the temperature range of 350–130 K. High temperature data yield activation energy gap which increases significantly with hydrogen content, while the low temperature conductivity is explained by hopping between localized states.     

Low energy excitations in amorphous metals

The low temperature properties of amorphous metals pertinent to the existence of low energy excitations are reviewed. In an introductory section, the currently accepted model for low energy excitations, i.e. the model of two level systems (TLS), is discussed. The treatment of amorphous metals focuses on the specific heat C, thermal conductivity κ, ultrasonic properties and electrical resistivity ?. Measurements of C and κ are often performed on amorphous superconductors in order to exclude the effect of conduction electrons. The TLS density of states and the TLS-phonon coupling in these materials as determined from C and κ respectively are surprisingly close to values for insulating glasses. Ultrasonic experiments carried out mostly on normal amorphous metals reveal a strongly enhanced TLS relaxation rate with respect to insulators. This can be attributed to TLS-electron coupling. The effect of this coupling on ? is uncertain at present. In order to obtain more insight into the microscopic origin of TLS in metallic and insulating glasses some examples of TLS in crystalline disordered solids are discussed. Finally, some formal analogies are drawn between spin glasses and real glasses.     

离子束反应溅射沉积SiO2薄膜的光学特性

 主要研究采用离子束反应溅射（RIBS）制备SiO2薄膜的折射率、消光系数、化学计量比与氧气在氩氧混合工作气体中含量及其沉积速率的关系。研究结果表明：RIBS制备的SiO2薄膜在0.63 μm处折射率n= 1.48,消光系数小于10-5;随着沉积速率的增加,薄膜的折射率和消光系数随之变大,当沉积速率超过0.3 nm/s,即使是在纯氧环境溅射,折射率值也不低于1.5;通过对红外透射光谱的主吸收峰位置研究得到沉积的SiO2薄膜为缺氧型,化学计量比不超过1.8,且红外吸收峰位置和SiO2折射率存在对应关系,因此在不加热衬底情况下使用RIBS制备SiO2薄膜时,会限制沉积速率的提高。     

Photothermal detection of surface states in amorphous silicon films

A new method for the determination of surface states in amorphous silicon films is proposed. The method is based on the observation of enhancement of the interference fringe amplitude in photothermal deflection spectra, due to the presence of surface states.A theoretical approach is presented, together with the experimental results and an evaluation of the density of surface states. The method proves to be adequate, in most cases, to yield results in good agreement with those reported in literature.     

Nickel induced lateral crystallization behavior of amorphous silicon films

Nickel induced lateral crystallization of amorphous silicon with and without electric field has been studied. Dendritic silicon growth behavior is observed, with crystallites of a few hundred nanometers in width and up to a few microns in length. The behavior can be understood from the preferential epitaxial growth of silicon from the (1 1 1) facets of the NiSi₂ precipitate, which forms during the early stage of the annealing process. The dendritic growth fronts are different with and without electric field in the nickel induced lateral crystallization process. Electric field is found to be beneficial in increasing the lateral crystallization rate and improving the film crystallinity. Joule heating plays an important role as well to enhance the lateral crystallization.     

氢化非晶硅薄膜的热导率研究

采用铂电极为加热电阻,研究了厚度为300—370nm等离子体化学气相沉积(PECVD)工艺制备的氢化非晶硅(a-Si：H)薄膜的热导率随衬底温度的变化规律.用光谱式椭偏仪拟合测量薄膜的厚度,得到了沉积速率随衬底温度变化规律,傅里叶红外(FTIR)表征了在KBr晶片衬底上制备的a-Si：H薄膜的红外光谱特性,SiH原子团键合模的震动对热量的吸收降低了薄膜热导率.从动力学角度分析了薄膜热导率随平均温度升高而增大的原因,并比较了声子传播和自由电子移动在a-Si：H薄膜热导率变化上的作用差异. 关键词： 非晶硅 热导率 薄膜 热能     

Photoluminescence analyses of hydrogenated amorphous silicon nitride thin films

Silicon-rich hydrogenated amorphous silicon nitride (a-SiN_x:H) films were grown by plasma enhanced chemical vapor deposition (PECVD) with different r=NH₃/SiH₄ gas flow ratios. The optical absorption characteristics were analyzed by Fourier transform infrared (FTIR) and UV-visible transmittance spectroscopies. The recombination properties were investigated via photoluminescence (PL) measurements. As r was increased from 2 to 9, the PL emission color could be adjusted from red to blue with the emission intensity high enough to be perceived by naked eye at room temperature. The behaviors of the PL peak energy and the PL band broadness with respect to the optical constants were discussed in the frame of electron-phonon coupling and band tail recombination models. A semiquantitative analysis supported the band tail recombination model, where the recombination was found to be favored when the carriers thermalize to an energy level at which the band tail density of states (DOS) reduces to some fraction of the relevant band edge DOS. For the PL efficiency comparison of the samples with different nitrogen contents, the PL intensity was corrected for the absorbed intensity fraction of the incident PL excitation source. The resulted correlation between the PL efficiency and the subgap absorption tail width further supported the band tail recombination model.