本征微晶硅薄膜孵化层的深入研究

采用VHF-PECVD技术沉积微晶硅薄膜,获得较高的生长速度,但是薄膜质量较差,这与初始生长过程中生成厚的非晶孵化层关系密切。本研究表明,孵化层的厚度与硅烷浓度、功率密切相关:低的硅烷浓度,能保证成膜过程中氢原子打破弱键的几率,逐层生长现象明显;大的馈入功率,能保证更多氢原子参与成膜反应,减少悬键缺陷。这两方面的优化,最终把孵化层降低到26.55 nm。     

本征微晶硅材料及其在电池中的应用

采用VHF-PECVD技术制备了系列不同硅烷浓度和功率的微晶硅薄膜.材料的电学特性和结构特性测试结果表明:制备出了符合太阳电池用的本征微晶硅薄膜.材料应用于电池中,制备出了效率达6.6%的微晶硅电池,没有ZnO背反射电极,而且电池的厚度仅为1.0 μm.     

脉冲磁控溅射沉积微晶硅薄膜工艺研究

采用脉冲磁控溅射法制备氢化微晶硅薄膜,利用X射线衍射、拉曼光谱、扫描电子显微镜和四探针测试仪对薄膜结构和电学性能进行表征和测试,研究了衬底温度、氢气稀释浓度和溅射功率对硅薄膜结构和性能的影响。结果表明:在一定范围内,通过控制合适的衬底温度、增大氢气稀释浓度及提高溅射功率,可以制备高质量的微晶硅薄膜。在衬底温度为400℃、氢气稀释浓度为90%及溅射功率为180W的条件下制备的微晶硅薄膜,其晶化率为72.2%,沉积速率为0.48nm/s。     

射频PECVD高速沉积微晶硅薄膜

本文采用射频等离子体增强化学气相沉积(RF-PECVD)技术高速沉积微晶硅薄膜。系统研究了射频功率、气体总流量、沉积气压、硅烷浓度等沉积参数对薄膜沉积速率和晶化率的影响。通过沉积参数的优化,使微晶硅薄膜沉积速率达到了3/s左右。     

微晶硅p-i-n薄膜太阳电池研究进展

相对于单晶硅和非晶硅来说,微晶硅薄膜太阳电池具有更多的优势。高速沉积高效微晶硅太阳电池已经成为当前研究的热点。综合介绍了微晶硅p-i-n太阳电池的结构以及基本原理、研究现状和存在的问题,并对其发展前景进行了展望。     

不同沉积速率下微晶硅薄膜的生长行为研究

鉴于微晶硅薄膜在沉积过程中先经历一个非晶过渡层才开始晶化的生长特点,试图通过降低薄膜的沉积速率来延长沉积原子在薄膜生长表面的扩散时间,以达到促进晶粒生长的目的。研究结果表明,反应气体气流量的减小可以有效降低薄膜的沉积速率;随着沉积速率的降低,薄膜的表面粗糙度明显减小,且其平均晶粒尺寸有所增大,通过HRTEM甚至能观察到尺寸在10nm以上的晶粒,说明沉积速率的降低对沉积粒子在薄膜生长表面的扩散过程有较大影响;另外,薄膜的少子寿命随着沉积速率的降低逐渐增大,这与薄膜结晶程度和平均晶粒尺寸的变化趋势一致,可见微观结构对电学性能起着决定作用。     

高速微晶硅薄膜沉积功率利用效率的测量与优化

为了实现低成本微晶硅薄膜的高速沉积,需要尽可能的优化工艺参数,特别是提高功率利用效率对于降低生产成本,以及提高工艺稳定性都具有重要的意义.文中对射频等离子体增强化学气相沉积系统的各部分功率消耗进行了测量与分析,发现实际用于辉光放电的功率利用率仅为10％以下;腔室的寄生电阻自身消耗功率占30％左右,且寄生电抗分布情况对匹配器的功率消耗影响较大.通过对系统硬件的改造,降低了寄生电抗的影响,显著地提高了功率耦合效率,在高反应气压条件下的功率利用率达到60％以上.     

不同沉积速率微晶硅薄膜生长模式的蒙特卡洛模拟研究

采用标度理论比较了不同速率下微晶硅薄膜的生长模式。结果是:低速时薄膜的生长指数为0.19,高速时薄膜的生长指数为0.61,两者生长机理明显不同。通过蒙特卡洛模拟薄膜生长过程,结果表明:生长基元的粘附系数和扩散能力对不同生长速率下薄膜的生长有较大的影响。     

PECVD法制备微晶硅薄膜的研究

对等离子体增强化学气相沉积技术(PECVD)制备的微晶硅(μc-Si)薄膜的电导率、光学带隙和晶化率随温度和功率的变化规律进行了研究.从拉曼谱中可以明显看出,随着功率的增大,N型材料的非晶肩逐渐减小,材料的晶化率增大.随着温度的升高,P型材料的暗电导率和激活能都是先升高后降低.     

用等离子体增强化学气相沉积制备微晶硅薄膜

以Ar+SiH_4作为反应气体,用电子回旋共振等离子体化学气相沉积(ECR PECVD)方法制备微晶硅薄膜,研究了微波功率对薄膜中H含量、薄膜的沉积速率、择优取向和结晶度的影响。结果表明,在300℃制备低温微晶硅薄膜,随着微波功率的增大,薄膜的沉积速率先增大后减小,微波功率为600 W时达到最大;而结晶度和薄膜中的H含量则分别呈现单调增大和单调减少的趋势;使用不同的微波功率,薄膜的择优取向均为(111)方向。     

Electronic transport properties of microcrystalline silicon thin films prepared by VHF-PECVD

Steady-state photocarrier grating (SSPG) and steady-state photoconductivity, _ph, experiments have been carried out to investigate the electronic transport properties of undoped hydrogenated microcrystalline silicon (c-Si : H) films prepared with very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Material with different crystalline volume fractions was obtained by variation of the silane concentration (SC) in the process gas mixture. Pure amorphous silicon material was investigated for comparison. The ambipolar diffusion length, L_amb, which is dominated by the minority carrier properties, is obtained both from the best fit to the experimental photocurrents ratio, , versus grating period (), and from the Balberg plot for the generation rates between 10¹⁹ and 10²¹ cm^–3 s^–1. L_amb increases from 86 nm with increasing SC and peaks around 200 nm for the SC=5.6% and decreases again for higher SCs. L_amb values obtained from the intercept of the Balberg plot result in a small difference of around 5% for most of the samples. Minority carrier mobility-lifetime ()-products are much lower than those of majority carriers, however, both majority and minority carrier -products in microcrystalline silicon are higher than those of undoped hydrogenated amorphous silicon. The grating quality factor (₀) changes from 0.70 to 1.0 indicating almost negligible surface roughness present in the samples.     

Conductance fluctuations in VHF-PECVD grown hydrogenated microcrystalline silicon thin films

Coplanar conductance fluctuations or excess noise of undoped hydrogenated microcrystalline silicon (μc-Si : H) thin films grown by VHF-PECVD from silane–hydrogen mixtures with silane concentrations from 2% to 6% have been studied between room temperature and 470 K. We report that undoped μc-Si : H thin films show similar noise-power spectra to those of undoped a-Si : H films in a coplanar sample geometry. At lower temperatures, the noise with the slope α=0.60±0.07 and at higher temperatures, the noise with the slope α close to unity dominate the spectrum. The noise magnitude decreases with decreasing silane concentration and becomes strongly temperature dependent with increased crystallinity.     

Hydrogenated microcrystalline silicon films prepared by VHF-PECVD and single junction solar cell

Intrinsic microcrystalline silicon films have been prepared with very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) from silane/hydrogen mixture at 180°C. The effect of silane concentration and discharge power on the growth of silicon films was investigated. Samples were investigated by Fourier transform infrared spectroscopy, Raman scattering and X-ray diffraction. The Raman spectrum shows that the morphological transition from microcrystalline to amorphous occurs under conditions of high silane concentration and low discharge power. X-ray diffraction spectra indicate a preferential growth direction of all microcrystalline silicon films in the (111) plane. In addition, a solar cell with an efficiency of 5.1% has been obtained with the intrinsic microcrystalline layer prepared at 10W.     

Poly-silicon thin films by aluminium induced crystallisation of microcrystalline silicon

Al-induced crystallisation of microcrystalline Si thin films prepared by electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) on glass and SiO₂ coated Si wafers has been studied. The starting structure was substrate/μc-Si/Al. Annealing this structure in the temperature range 370-520 °C, immediately following deposition of the Al layer, resulted in successful layer exchange and the formation of a substrate/Al+Si layer/poly-Si geometry. The top poly-Si layer exhibited grain sizes generally in the range ∼2-6 μm, although larger grains were also sparsely present. The films did not exhibit any appreciable degree of preferred orientation. The surface roughness was relatively high with a R_a value of ∼20 nm.     

Microstructure characterization of microcrystalline silicon thin films deposited by very high frequency plasma-enhanced chemical vapor deposition by spectroscopic ellipsometry

We applied ex situ spectroscopic ellipsometry (SE) on silicon thin films across the a-Si:H/μc-Si:H transition deposited using different hydrogen dilutions at a high pressure by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). The optical models were based on effective medium approximation (EMA) and effective to estimate the thickness of the amorphous incubation layer and the volume fractions of amorphous, microcrystalline phase and void in μc-Si:H thin films. We obtained an acceptable data fit and the SE results were consistent with that from Raman spectroscopy and atomic force microscopy (AFM). We found a thick incubation layer in μc-Si:H thin films deposited at a high rate of ~ 5 Å/s and this microstructure strongly affected their conductivity.     

Photoconductivity spectroscopy in hydrogenated microcrystalline silicon thin films

Steady-state photoconductivity and sub-bandgap absorption measurements by the dual-beam photoconductivity (DBP) method were carried out on undoped hydrogenated microcrystalline silicon thin films prepared by VHF-PECVD and hot-wire chemical vapor deposition. The results are compared with those of the constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS). It is found that DBP, CPM, and PDS provide complementary data on the optoelectronic processes in microcrystalline silicon.     

Quantitative analysis of tungsten, oxygen and carbon concentrations in the microcrystalline silicon films deposited by hot-wire CVD

In order for hot-wire chemical vapor deposition to compete with the conventional plasma-enhanced chemical vapor deposition technique for the deposition of microcrystalline silicon, a number of key scientific problems should be cleared up. Among these points, the concentration of tungsten (nature of the filament), as well as the concentration of oxygen and carbon (elements issued when vacuum is broken between two runs), should not exceed threshold values, beyond which electronic properties of the films could be degraded, as in the case of monocrystalline silicon. Quantitative chemical analysis of these elements has been carried out using the secondary ion mass spectrometry technique through depth profiles. It has been shown that for a high effective filament surface area (S_f=27 cm²), the W content increases steadily from 5×10¹⁴ to 2×10¹⁸ atoms cm⁻³ when the filament temperature T_f increases from 1500 to 1800 °C. For a fixed T_f, the W content increases with the effective surface area S_f. Thus, considering our reactor geometry, the W content does not exceed the detection limit (5×10¹⁴ atoms cm⁻³) when T_f and S_f are limited to 1600 °C and 4 cm², respectively. For O and C elements, under deposition conditions of high dilution of silane in hydrogen (96%), O and C concentrations approaching 10²⁰ atoms cm⁻³ have been obtained. The introduction of an inner vessel inside the reactor, the addition of a load-lock chamber and a decrease in substrate temperature to 300 °C have led to a drastic decrease in these contents down to 3×10¹⁸ atoms cm⁻³, compatible with the realization of 6% efficiency HWCVD μc-Si:H solar cells.     

Effects of dilution ratio and seed layer on the crystallinity of microcrystalline silicon thin films deposited by hot-wire chemical vapor deposition

We deposited microcrystalline silicon (μc-Si) by hot-wire chemical vapor deposition (HWCVD) at different thickness and dilution ratio, with and without seed layer. As the dilution ratio increased, we observed an increase in the amount of microcrystalline phase in the film, a change in the structure of the grains and a loss of the (220) preferential orientation. The films deposited over a seed layer had a larger fraction of crystalline phase than films deposited with the same parameters but without a seed layer. For high dilution ratios (R=100), most of the film grows epitaxially at the interface with the Si substrate, but a microcrystalline film slowly replaces the single-crystal phase. For low dilution ratios (R=14), the film starts growing mostly amorphously, but the amount of crystalline phase increases with thickness.     

Low-temperature PECVD deposition of highly conductive microcrystalline silicon thin films

In this paper, we present the characterization results of doped n-type microcrystalline hydrogenated-silicon (c-Si : H) films deposited in a plasma-enhanced chemical vapor deposition in the temperature range between 70 and 250 °C. The interest in these films arises from the fact that they combine the high optical absorption of amorphous silicon with the electronic behavior of the crystalline silicon, making them interesting for the production of large electronic devices such as solar cells, image sensors, and flat panels. It is shown that n-type c-Si : H films with high electrical conductivity can be obtained even at low temperature deposition, around 120 °C (=2.9 S cm^–1). The structural properties of the films have been studied by Raman and infrared spectroscopy that allowed for the determination of the crystalline fraction. Electrical measurements were performed by a.c. impedance spectroscopy, Hall effect, and dark conductivity. Characteristics suitable for application in electronic devices were obtained with the developed deposition parameters set-up; the best dark conductivity values were around 1 S cm^–1 for deposition temperatures within the 120–140 °C range. Some conclusions regarding the correlation between electrical and structural properties are presented for the considered temperature range.     

Ta上生长的硅薄膜退火的微晶化研究

对射频溅射功率80W条件下Ta缓冲层上生长的硅薄膜进行退火并用Raman散射和X射线衍射技术对样品的微观结构进行检测,系统研究了退火温度和退火时间对硅薄膜结晶性的影响.分析结果表明,在560℃退火2h或680℃退火1h之后,硅薄膜开始晶化,并且随着退火温度的增加或退火时间延长,薄膜逐渐由非晶向微晶转变.获得了可用于太阳能电池的微晶硅薄膜的最佳晶化参数.