微波ECR CVD法制备a-Si:H膜的氢含量研究

应用微波电子回旋共振化学气相沉积(MWECR CVD)方法,在较高速率下沉积了a-SiH薄膜,用FTIR红外谱仪研究a-SiH薄膜的结构特性与衬底温度、氢稀释比、光学带隙的对应关系,并对2000cm-1附近的特征吸收峰用高斯函数进行了拟合分析,获得了沉积高质量a-SiH薄膜的最佳工艺条件.     

Effect of substrate on hydrogen in and out diffusion from a-Si:H thin films

We present a detailed study on the effect of the substrate on the structure and hydrogen evolution from p-type hydrogenated amorphous silicon thin films co-deposited on the grounded and RF electrodes of an asymmetric radio frequency glow discharge reactor, as well as the similar films exposed to an hydrogen plasma. We used spectroscopic ellipsometry and hydrogen evolution measurements to analyze the effects of the substrate, ion energy and hydrogen plasma on the films microstructure, thickness, hydrogen content, hydrogen binding and hydrogen evolution. The hydrogen evolution spectra show a strong substrate dependence. In particular on crystalline silicon substrate, we observe the formation of bubbles. For the various substrates, ion energy and hydrogen plasma treatment do not affect the hydrogen evolution spectra. These results indicate that the action of hydrogen in a-Si:H is modified by the nature of the substrate.     

Microcrystalline silicon growth on a-Si:H: effects of hydrogen

Spectroscopic ellipsometry and secondary ion mass spectrometry have been performed on structures consisting of a microcrystalline silicon film deposited on different a-Si:H substrates. The substitution of hydrogen by deuterium in the microcrystalline growth allowed us to quantify the long-range effects of hydrogen and to distinguish between the different layers. The thicknesses deduced from ellipsometry measurements were in excellent agreement with the secondary ion mass spectrometry profiles. Moreover, we clearly show that the a-Si:H film on which the microcrystalline silicon is deposited can be modified because of the diffusion of hydrogen necessary to the formation of the microcrystalline silicon. However, this modification strongly depends on the deposition conditions and abrupt interfaces can be achieved in some cases.     

Crystallization by excimer laser annealing for a-Si:H films with low hydrogen content prepared by Cat-CVD

Crystallization by excimer-laser annealing (ELA) for hydrogenated amorphous silicon (a-Si:H) films with low hydrogen content (C_H) prepared by catalytic chemical vapor deposition (Cat-CVD) was systematically studied. From optical microscopy images, no hydrogen bubbling was observed during ELA, even without a dehydrogenation process. As the laser energy density was increased to 300 mJ cm⁻², the full width at half-maximum of the Raman signal from the crystalline phase decreased to approximately 4 cm⁻¹. This value is almost equal to or even smaller than that reported for polycrystalline Si (poly-Si) films prepared from plasma-enhanced CVD (PECVD) a-Si:H films by ELA so far. The average grain size, estimated from scanning electron microscopy, was approximately 500 nm for C_H of 1.3 at.%. On the other hand, the grain size of poly-Si films prepared from PECVD a-Si:H films with a dehydrogenation process was only 200 nm. The technique using Cat-CVD films is expected to be used for fabrication of low-temperature high-mobility thin-film transistors.     

a-Si:H film on side-polished fiber as optical polarizer and narrow-band filter

An optical waveguide structure consisting of side-polished single-mode fiber covered with thin a-Si:H planar waveguide is studied as a channel-dropping narrow-band filter and fiber-optic polarizer. Spectral and polarization characteristics of the structure are measured in the wavelength region of 600–1600 nm, for the different values of the a-Si:H film thickness and the superstrate refractive index. The FWHM of the filter is about 8 nm for the asymmetric waveguide and 10 nm for the symmetric one. The discrimination of the resonance minima for two polarizations varies from several tens for the symmetric PWG up to several hundreds of nanometers for the asymmetric PWG. The optical losses in the off-resonance region are less than 0.3 dB. The measured value of the extinction coefficient of the fiber-optical polarizer is 32.5 dB.     

Micropore density in a-Si:H and a-Si:H:Cl films

a-Si:H films deposited from various silane-containing gas mixtures have been studied regarding their porosity. Micropore densities of 2.O × 10²cm^-2, 5.0 × 10⁴cm^-2 and 5.0 × 10⁴cm^-2 were determined for a-Si:H:C1, a-Si:H(H₂) and a-Si:H(Ar) films, respectively. It is suggested that these values correlate with the structural properties of the films, so that a-Si:H:Cl films seem to be the most uniform on the microstructural scale.     

Effect of film thickness and curing temperature on the sensitivity of ZnO:Sb thick-film hydrogen sensor

This paper reports the effect of film thickness and curing temperature on the sensitivity of the screen-printed thick-film ZnO (incorporated with 7 wt%Sb) H₂, CO and CH₄ sensors. The sensitivity of the sensors increases up to 60 μm and decreases for higher film thickness. Increase in the curing temperature of the films, decreases the sensitivity of the sensors because of the increase in the average grain size, as observed by scanning electron microscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quantitative hydrogen measurements in PECVD and HWCVD a-Si:H using FTIR spectroscopy

A series of hydrogenated amorphous silicon films have been deposited using plasma enhanced chemical vapour deposition (PECVD) and hot-wire chemical vapour deposition (HWCVD) techniques. The total concentration of bonded hydrogen in the films was varied between 3% and 18% as determined by hydrogen effusion measurements. Fourier transform infra-red (FTIR) spectra of the PECVD and HWCVD samples exhibit strong absorption peaks that correspond to Si–H bend and stretch modes, and Si–H₂ stretch modes. A quantitative fit of the FTIR peak areas to the hydrogen effusion concentrations reveals that there is reasonable agreement between the required proportionality constants in PECVD and HWCVD material for the Si–H bend and stretch modes. The uncertainty error for the FTIR proportionality constants is consistently greater for the HWCVD data set, however, which may indicate that the effective dynamical charge of the Si–H dipoles is perturbed in the HWCVD material by bonded impurities that are sourced from the tungsten wire.     

a-Si∶H及其多层膜光致发光某些性质的研究

本文研究了 a-Si∶H 及 a-Si∶H/a-SiN_x∶H 多层膜光致发光的某些性质。实验研究表明,a-Si∶H 及其多层膜的光致发光峰值能量强烈地依赖于沉积偏压、a-Si∶H 层厚度和内应力,并对这些结果进行了讨论。     

Characteristics of a linear array of a-Si:H thin film position sensitive detector

The increasing demand in automation processes in finishing techniques also calls for automatic measurement and inspection methods. These methods ought to be installed as close as possible to the production process and they ought to measure the values needed in a safe and fast way, without disturbing the process itself. Simultaneously they should be free of wear and insensitive against mechanical perturbations. This approach can be reached by proper combination of the laser triangulation technique with an array of linear position sensitive detectors, able to supply information about the surface finishing of an object. This is the aim of this paper that envisages to present experimental results of the performances exhibited by such an array constituting 128 elements. The analogue information supplied by this array is processed by an analogue/digital converter, directly coupled to the array and whose information is computer processed, concerning the recognition of patterns and the processing of information collected over the object to be inspected.     

PCVD法沉积a-Si:H薄膜初始阶段的计算机模拟

利用Monte Carlo模型研究了用PCVD法沉积α-Si:H薄膜初始阶段团簇的大小和数目与衬底温度的关系。该模型考虑了两个成长阶段,即成核阶段和晶核成长阶段;3种动力学过程,即粒子入射,吸附粒子扩散和吸附粒子脱附过程。模拟结果表明,随着衬底温度的升高,团簇的数目和大小都有所增长,且存在一个最佳温度550K,使团簇的数目达到饱和,晶粒为最大,与实验结果基本相符。     

Effect of thickness on H2 gas sensitivity of SnO2 nanoparticle-based thick film resistors

The effect of thickness on the p.p.m. level H₂ gas sensitivity of SnO₂ nanoparticle-based thick film resistors is reported. The nanoparticles are synthesized by a sol-gel method and the films are prepared using standard screen printing technology. The thickness of the films is varied from a few micrometers to a few hundred micrometers. The results indicate that the sample having thickness 76 m gives the maximum sensitivity. The mechanism of the change in sensitivity with thickness is discussed.     

a-Si:H p–i–n structures with extreme i-layer thickness

We present measurements and numerical simulation of a-Si:H p–i–n detectors with a wide range of intrinsic layer thickness between 2 and 10 µm. Such a large active layer thickness is required in applications like elementary particle detectors or X-ray detectors. For large thickness and depending on the applied bias, we observe a sharp peak in the spectral response in the red region near 700 nm. Simulation results obtained with the program ASCA are in agreement with the measurement and permit the explanation of the experimental data. In thick samples holes recombine or are trapped before reaching the contacts, and the conduction mechanism is fully electron dominated. As a consequence, the peak position in the spectral response is located near the optical band gap of the a-Si:H i-layer.     

退火对 a-Si∶H/a-SiN_x∶H 多层膜光致发光和红外吸收谱的影响

本文报道了经300℃到800℃退火后的氢化非晶硅(a-Si∶H)/氢化非晶氮化硅(a-SiN_x∶H)多层膜77K 的光致发光性能。77K 的光致发光峰值能量随 T_a 增加而减少,其减少速度对几种样品是不同的,由厚度为20(?)的 a-Si∶H 子层组成的多层膜(d_(?)=20(?))要来得慢。当退火温度达到800℃时,d_(?)=20(?)的多层膜仍保留有光致发光特性,而对于 d_(?)=300(?)多层膜和单层 a-Si∶H 膜,当退火到600℃后光致发光特性已消失。文中提出了不同 a-Si∶H 子层厚度的多层膜光致发光特性上的差别是与 a-Si∶H/a-SiN_x∶H 界面氢比体内氢热稳定性来得高有关。后者由多层膜的红外吸收谱与退火温度依赖关系得到证实。     

a-Si∶H/a-Ge∶H超晶格的界面特性研究

本文用红外(IR)和拉曼(Raman)谱研究了反应溅射 a-Si∶H/a-Ge∶H 超晶格的界面特性.定量分析发现,界面处没有因应力释放引起的 H 富集,不存在由超晶格结构引起的界面结构无序,界面处存在着～(5±2)(?)的 Si、Ge 组分混合层.我们对结果进行了初步分析.     

An a-Si:H/SiGe/Si punchthrough heterojunction phototransistors with an thin-Al film

An a-Si:H/SiGe/Si punchthrough heterojunction phototransistors (PTHPTs), responding to a wavelength of 850 nm, have been proposed and demonstrated in this work. The dramatic difference between PTHPTs and conventional heterojunction phototransistors is that the base is completely depleted in the PTHPTs, thus a larger optical gain is achieved due to the lack of a neutral base. Furthermore, the use of low-temperature a-Si:H instead of conventional crystalline silicon, a strained SiGe can be preserved at the interface of base and emitter, allowing ultrashallow junctions and abrupt doping profiles. Another advantage is that the a-Si:H can provide large valence-band discontinuity between base and emitter, avoiding photogenerated holes injected from base to emitter, and hence a larger collector current. In addition, we employed a thin Al-coating covered on the surface of emitter to enhance the collection of photogenerated holes. In comparison to the PTHPTS without the thin-Al coating, the optical gain of PTHPTs with thin-Al coating is increased from 922 to 3970 at 5-V bias voltage, responding to a light source of 850 nm with 0.028 mW.     

Influence of potential fluctuations on photoconductivity in a-Si : H

The effects of long-range potential fluctuations (LRPF) on the d.c. and a.c. photoconductivities of undoped hydrogenated amorphous silicon (a-Si : H) have been discussed in the temperature region 20–300 K. It is found that the a.c. photoconductivity in the entire temperature range is dominated by dielectric relaxation, and not by any electronic hopping motion. A reasonable fit of the experimental data to a model calculation based on LRPF is obtained, and the extent of the potential fluctuations is deduced to be ～0.06 eV in energy and ～10 nm on a length scale.     

a-Si:H薄膜的制备工艺对其光电特性的影响

采用MW-ECR CVD方法制备的a-SiH薄膜在模拟太阳光照射下进行光敏性(σp.σ d)和光致衰退测试.对比了有、无热丝辅助沉积的薄膜的光电特性,得出沉积温度是影响薄膜光敏性的主要因素,而适当温度的热丝辅助对于薄膜的光致衰退有一定延缓作用.     

Thermal annealing of protocrystalline a-Si:H

It proves difficult to obtain a set of protocrystalline silicon materials with different characteristics from the same deposition chamber to study the exact nature of these transition region materials. Hot-wire deposited protocrystalline silicon was thus isochronically annealed at different temperatures to investigate the bonded hydrogen configurations and structural disorder. Modeling of optical reflection and transmission spectra with Scout^® yielded the optical parameters and infrared spectroscopy confirms that bonded hydrogen remains in the material, with the exception of a longer anneal of six hours at 520 °C. Sub bandgap absorption as inferred from photothermal deflection spectroscopy was related to these characteristics.     

Role of the resistive layer on the performances of 2D a-Si:H thin film position sensitive detectors

The aim of this work is to present an analytical model which can to interpret the role of the collecting resistive layer on the static performances exhibited by 2D amorphous silicon hydrogenated p–i–n thin film position sensitive detectors. In addition, experimental results concerning the device linearity and spatial resolution are presented and checked against the predicted values of the analytical model proposed.