硼掺杂对非晶硅薄膜微结构和光电性能的影响

以硅烷 (SiH4 )和硼烷 (B2 H6)为气相反应先驱体 ,采用等离子体增强化学气相沉积法 (PECVD)制备出轻掺硼非晶氢硅薄膜。X射线衍射、原子力显微镜和光、暗电导测试表明 ,一定程度的硼掺杂提高了非晶氢硅薄膜的电导率 ,降低了非晶氢硅薄膜的光、暗电导比 ,并促进了非晶氢硅薄膜中硅微晶粒的生长。红外吸收谱研究预示了大量的硼原子与硅、氢原子之间能形成某些形式的复合体 ,仅有少量硼元素对P型掺杂有贡献。     

硼掺杂对非晶硅薄膜微结构和光电性能的影响

以硅烷（SiH4)和硼烷（B2H6）为气相应反应先驱体，采用等离子体增强化学气相沉积法（PECVD）制备出轻掺硼非昌氢硅薄膜，X射线衍射，原子力显微镜和光，暗电导测试表明，一定程度的硼掺杂提高了非晶氢硅薄膜的电导率，降低了非晶氢硅薄膜的光，暗电导比，并促进了非晶氢硅薄膜中硅微晶粒的生长，红外吸为研究预示了大量的硼原子与硅，氢原子之间能形成某些形式的复合体，仅有少量硼元素对P型掺杂有贡献。     

硼掺杂对PECVD制备的纳米非晶硅薄膜电学行为的影响

本文采用PECVD法制备硼掺杂纳米非晶硅薄膜(na-Si:H),系统研究了掺杂气体比(B2H6/SiH4)、衬底温度Ts、RF电源功率对薄膜电学性能的影响.研究表明,与传统掺硼非品硅不同,随硼掺杂浓度的增加,掺硼na-Si:H薄膜的电导率先减小后增大并最终趋于饱和,其电导激活能E≈0.50eV、σph/σd＞102,具有应用于太阳能电池p型层的潜力.     

掺磷硅薄膜的微结构及光电特性研究

采用拉曼（Raman）散射谱、扫描电子显微镜（SEM）和X射线衍射（XRD）对掺磷硅薄膜的微结构进行了分析,并对掺杂前后薄膜的暗电导进行了测试,结果表明：掺P后导致薄膜的非晶化.与本征μc-Si：H薄膜相比,掺杂后薄膜暗电导率略有降低,同时在紫外-可见光区的透光率降低,但降低的程度与具体的沉积条件有关,同时研究发现掺杂薄膜容易进行快速光热退火晶化.     

高电导率高晶化率p型微晶硅薄膜的制备

利用射频等离子体增强化学气相沉积(RF-PECVD)技术,以B2H6为掺杂剂,在玻璃衬底上制备了厚度为40nm左右的p型微晶硅薄膜.为获得高电导率高晶化率的薄膜,采用正交实验法对衬底温度、氢稀释比及硼烷掺杂比等主要沉积参数进行初步优化.Raman光谱和电导率测试结果表明:(1)在实验选取的参数范围内,衬底温度是影响薄膜暗电导率和晶化率的最主要因素,其次是氢稀释比,硼烷掺杂比的影响相对较小;(2)通过正交优化,获得了暗电导率为2.05S·cm-1、晶化率为86%的p型微晶硅薄膜.     

掺硼纳米非晶硅的太阳能电池窗口层应用研究

本文通过等离子体增强化学气相沉积(PECVD)法沉积p型纳米非晶硅薄膜(na-si:H),系统地研究了掺杂气体比(B2H6/SIH4)、沉积温度、射频电源功率对薄膜结构、光学、电学性能的影响.研究表明,轻掺硼有利于非晶硅薄膜晶化,但随着掺硼量的增加,硼的"毒化"作用又使薄膜变为非晶态;与p型a_si:H相比,掺硼纳米硅薄膜的光学带隙Eopt较高,电导率较高,电导激活能较低,是一种很有潜力的太阳能电池窗口层材料.     

非晶硅光敏材料的高电阻率化研究

本文研究了用于制造非晶硅感光鼓的高阻非晶硅光敏材料，通过微量掺Ｂ、Ｏ，控制ａ－Ｓｉ：Ｈ薄膜中的ＳｉＨ２和ＳｉＨ基团的组成比，有效地实现了非晶硅材料的高电阻率化，其暗电阻率ρｄ≥１０＾１３Ω·ｃｍ，在可见了光至近红外光范围内，具有很高的单色光电导增益，σｐｈ／σｄ≥１０＾３。分析了ａ－Ｓｉ：Ｈ［Ｂ、Ｏ］材料ＩＲ谱的特征，说明了氧原子和硅－氢基团对微结构的影响及其在支配非晶硅光电性能方面的重要作用。     

热处理温度及掺硼对富硅氧化硅发光的影响

利用等离子体增强化学气相沉积制备了未掺杂与掺硼富硅氧化硅薄膜。在高纯N2气氛中经过600℃、800℃和1100℃热处理,发现随着热处理温度的升高,富硅氧化硅薄膜的光致发光发生了明显红移。这表明薄膜的光致发光来源逐渐由薄膜中的发光中心演变为硅纳米晶。在经过1100℃热处理的未掺杂与掺硼样品中,掺硼样品光致发光强度有明显减弱,这是由俄歇复合效应引起的。此外,在ESR测试谱中,掺硼样品的g因子为2.0020,这表明掺硼可以在薄膜基体和硅纳米晶之间的界面引入发光中心。     

纳米硅薄膜的低压化学气相沉积和电学性能研究

利用普通低压化学气相沉积技术在玻璃衬底上制备了大面积的纳米硅薄膜。不同温度下薄膜暗电导率的测试研究表明，薄膜的室温暗电导率随成膜温度的升高而增加，相应的电导激活能降低。热激活隧道击空机制可以较好地解释纳米硅薄膜特殊的电学性能。原位后续热处理研究表明，延长热处理时间以及采用低温成膜、高温后续退火的热处理方法均能有效提高其室温暗电导率。     

硼硫共掺杂金刚石薄膜的研究

利用微波等离子体化学气相沉积(MPCVD)技术,以丙酮为碳源．用二甲基二硫和三氧化二硼作掺杂源．在硅衬底上制备了硼与硫共掺杂的金刚石薄膜。用俄歇谱分析金刚石薄膜中硫的含量．用傅里叶红外光谱(FTIR)分析了薄膜表面键结构．用扫描电子显微镜(SEM)观测薄膜的表面形貌．X射线衍射(XRD)和喇曼(Raman)光谱表征膜层的结构。结果表明：微量硼的加入促进硫在金刚石中的固溶度,使硫在金刚石中的掺杂率提高了近50％;随着薄膜中硫含量的增加．薄膜的导电性增加,当薄膜中硫含量达到0．15％(原子分数)时其导电激活能为0.39eV。     

硼轻掺杂对a-Si∶H光电导层性能影响的研究

用等离子体增强化学气相沉积法制备了厚为1μm左右的B轻掺杂a-Si∶H光电导层，得到了a-Si∶H的暗电导率与淀积工艺参数和B掺杂比关系的实验曲线，利用该曲线确定了最佳工艺参数和最佳掺杂比。测量了最佳参数下淀积的a-Si∶H薄膜的电学和光学性能及其受掺杂比的影响。结果表明，当B掺杂比增大时，a-Si∶H的暗电导率先减小后增大，并可发生几个数量级的变化。光电导率减小，折射率略有降低，线性吸收系数显著增大，光学带隙减小。测量的数据表明，我们制备的B轻掺杂a-Si∶H光电导层满足投影机用液晶光阀的要求。     

Structural, electrical and optical characterization of N- and P-type SiC:H films deposited using ECR-CVD

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) method from a mixture of methane, silane and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the diborane and phosphine levels on the optical bandgap and conductivity were investigated. In the case of boron-doped films, there is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were largely amorphous and the bandgap decreases as the diborane levels are highly conductive and contains the whereas films deposited at a high microwave power of 800 W at low diborane levels are highly conductive and contains the silicon microcrystalline phase. These films become amorphous as the diborane level is increased, while the optical bandgap remains relatively unaffected throughout the entire range of diborane levels investigated. In the case of phosphorus-doped films, Raman scattering analysis showed that the deposition conditions strongly influence the structural, optical and electrical properties of the SiC:H films. Unlike boron doping, doping with phosphorus can have the effect of increasing the silicon microcrystalline phase in the SiC:H films which were prepared at low (150 W) and high (600 W) microwave powers. Films prepared at high microwave power showed only small variations in the optical bandgap, suggesting that good phosphorus doping efficiency can be achieved in films which contain the silicon microcrystalline phase (mc-SiC:H).     

A Raman and photoconductivity analysis of boron-doped SiC : H films deposited using the electron cyclotron resonance method

Hydrogenated amorphous silicon carbide films (a-SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition technique from a mixture of methane, silane and hydrogen, with diborane as the doping gas. The effect of the microwave power on the deposition rate were studied, and variations in the photo and dark conductivities were investigated in conjunction with film analysis using the Raman scattering technique. The conductivity increases rapidly to a maximum, followed by rapid reduction at high microwave powers. The ratio of the photo to dark conductivity, σph/σd, peaks at microwave powers of ∼600 W. Under conditions of high hydrogen dilution and increasing microwave power, Raman scattering analysis showed evidence of the formation and increase of microcrystalline silicon and diamond-like components in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity. This revised version was published online in November 2006 with corrections to the Cover Date.     

A Comparative Study of Boron and Phosphorus Doping Effects in SiC: H Films Prepared by ECR-CVD

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique from a mixture of methane, silane and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the microwave power on the deposition rate and optical bandgap were investigated, and variations in the photoand dark-conductivities and activation energy were studied in conjunction with film analysis using the Raman scattering technique. In the case of boron-doped samples, the conductivity increased rapidly to a maximum, followed by rapid reduction at high microwave power. The ratio of the photo- to dark-conductivity (σph/σd) peaked at microwave power of ~600 W. Under conditions of high microwave power, Raman scattering analysis showed evidence of the formation and increase in the silicon microcrystalline and diamond-like phases in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity.In the case of phosphorusdoped SiC:H samples, it was found that increase in the microwave power has the effect of enhancing the formation of the silicon microcrystalline phase in the films which occurred in correspondence to a rapid increase in the conductivity and reduction in the activation energy The conductivity increase stabilised in samples deposited at microwave power exceeding 500 W probably as a result of dopant saturation. Results from Raman scattering measurements also showed that phosphorus doping had the effect of enhancing the formation of the silicon microcrystals in the film whereas the presence of boron had the effect of preserving the amorphous structure.     

Effects of doping concentration on the microstructural and optoelectrical properties of boron doped amorphous and nanocrystalline silicon films

Boron doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique at various flow rate of diborane (F_B). As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The effect of boron concentration on the microstructural, optical and electrical properties of the films was investigated. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the dark conductivity of doped amorphous samples increases monotonously with the increase of doping content. While the dark conductivity of doped nc-Si films is not only determined by the concentration of dopant but also the crystallinity of the films. As increasing the flow rate of diborane, the crystallinity of doped nc-Si films decreases, which causes the decrease of dark conductivity. Finally, the high dark conductivity of 178.68 S cm⁻¹ of the B-doped nc-Si thin films can be obtained.     

Electronic properties of bottom gate silicon nitride/hydrogenated amorphous silicon structures

The electronic properties of silicon nitride/hydrogenated amorphous silicon (SiN/a-Si:H) interfaces are studied with complementary techniques: quasistatic capacitance measurements achieved on c-Si/SiN/a-Si:H/Al MIS structures, and dark conductivity, steady-state photoconductivity and modulated photocurrent (MPC) experiments performed on glass/a-Si:H and glass/SiN/a-Si:H samples fitted with two coplanar Al electrodes, using the same SiN and aSi:H layers as in the MIS structures. Results of bias annealing experiments on the MIS structures are explained in the framework of the defect-pool model taking account of a fixed positive charge in the insulator, which should yield a slight electron accumulation in the a-Si:H close to the SiN/a-Si:H interface under zero bias equilibrium conditions. This electron accumulation is clearly put into evidence from the experiments carried out on the coplanar samples, where we observe that the conductivities in the dark and under illumination are much higher in presence of the bottom SiN layer. The SiN layer also induces a significant decrease of the density of states above the Fermi level determined from MPC, which also confirms the changes in the defect density stated by the capacitance measurements and in agreement with the defect-pool model predictions.     

Fine particle removal by a negatively-charged fine particle collector in silane plasma

To suppress inclusion of fine particles in amorphous silicon films, a negatively-charged fine particle (NFP) collector has been successfully installed in a silane plasma. Two modes of operation of the NFP collector biasing were examined: (i) turning on after the appearance of fine particles; and (ii) turning on from the very beginning of the plasma operation. While the former proved the effectiveness of the NFP collector in the removal of fine particles, apparently very small particles (<100 nm) removal in the latter reduced the degradation of the photo conductivity in deposited a-Si:H films by light soaking. This effect is accompanied by the increased density of SiH bonding, which can be related to the possible modification in the silicon networks in the amorphous film.     

Effect of Si/Fe ratio on the boron and phosphorus doping efficiency of β-FeSi2 by magnetron sputtering

Boron-doped or phosphorus-doped β-FeSi₂ thin films have been prepared on silicon substrate by magnetron sputtering. Effects of Si/Fe ratio on the boron and phosphorus doping efficiencies have been studied from the resistivities of doped β-FeSi₂ thin films and current-voltage characteristics of doped β-FeSi₂/Si heterojunctions. The experimental results reveal that the carrier concentration and doping efficiency of boron or phosphorus dopants at the Fe-rich side are higher than that at the Si-rich side. The effect of Si/Fe ratio can be deduced from the comparison of the formation energies under two extreme conditions. At the Fe-rich limit condition, the formation energy of boron or phosphorous doping is lower than that at the Si-rich condition. Therefore, the activation of impurities is more effective at the Fe-rich side. These results demonstrate that the boron-doped and phosphorous-doped β-FeSi₂ thin films should be kept at the Fe-rich side to avoid the unexpected doping sites and low doping efficiency.     

Microwave power dependence of the optical and structural properties of boron and phosphorus-doped SiC:H films prepared using ECR-CVD

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique from a mixture of methane, silane and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the microwave power on the deposition rate and optical bandgap were investigated, and variations in the photo- and dark-conductivities were studied in conjunction with film analysis using the Raman scattering technique. In the case of boron-doped samples, the conductivity increased rapidly to a maximum, followed by rapid reduction at high microwave powers. The ratio of the photo- to dark-conductivity (σ_ph/σ_d) peaked at microwave power of 600 W. Under conditions of high microwave power, Raman scattering analysis showed evidence of the formation and increase in the silicon microcrystalline and diamond-like phases in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity. In the case of phosphorus-doped SiC:H samples, it was found that increase in the microwave power has the effect of enhancing the formation of the silicon microcrystalline phase in the films which occurred in correspondence to a rapid increase in the conductivity. The conductivity increase stabilised in samples deposited at microwave powers exceeding 500 W probably as a result of dopant saturation. Results from Raman scattering measurements also showed that phosphorus doping has the effect of enhancing the formation of the silicon microcrystals in the film whereas the presence of boron has the effect of preserving the amorphous structure.