氢化非晶硅薄膜中氢含量及键合模式的红外分析

Fourier红外透射(FTIR)谱技术是研究氢化非晶硅（a-Si∶H）薄膜中氢的含量（CH）及硅—氢键合模式（Si-Hn）最有效的手段.对用等离子体化学气相沉积（PCVD）方法在不同的衬底温度（Ts）下制备出的氢化非晶硅薄膜，通过红外透射光谱的基线拟合、高斯拟合分析，得到了薄膜中的氢含量，硅氢键合模式及其组分，并分析了这些参量随衬底温度变化的规律.     

氢化纳米硅薄膜中氢的键合特征及其能带结构分析

对氢化纳米硅薄膜中氢的键合特征和薄膜能带结构之间的关系进行了研究.所用样品采用螺 旋波等离子体化学气相沉积技术制备，利用Raman散射、红外吸收和光学吸收技术对薄膜的 微观结构、氢的键合特征以及能带结构特性进行了分析.Raman结果显示不同衬底温度下所生 长薄膜的微观结构存在显著差异，从非晶硅到纳米晶硅转化的衬底温度阈值为200℃.薄膜中 氢的键合特征与薄膜的能带结构密切相关.氢化非晶硅薄膜具有较高的氢含量，因键合氢引 起的价带化学位移和低衬底温度决定的结构无序性，使薄膜呈现较大的光学带隙和带尾宽度 .升 关键词： 氢化纳米硅 螺旋波等离子体 能带结构     

高氢稀释制备微晶硅薄膜微结构的研究

采用高氢稀硅烷热丝化学气相沉积方法制备氢化微晶硅薄膜.其结构特征用Raman谱，红外透射谱，小角X射线散射等来表征.结果表明微晶硅的大小及在薄膜中的晶态比χ_c随氢稀释度的提高而增加.而从红外谱计算得到氢含量则随氢稀释度的增加而减少.小角X射线散射结果表明薄膜致密度随氢稀释度的增加而增加.结合红外谱和小角X射线散射的结果讨论与比较了不同相结构下硅网络中H的键合状态.认为随着晶化的发生和晶化程度的提高H逐渐移向晶粒表面，在硅薄膜中H的存在形式从以SiH为主向SiH₂ 关键词：     

氢稀释对纳米晶硅薄膜晶化特性的影响及薄膜生长机理

以SiH4与H2作为前驱气体,采用射频等离子增强化学气相沉积技术制备了纳米晶硅薄膜.利用Raman散射和红外吸收光谱等技术,对不同氢稀释比条件下薄膜的微观结构和键合特性进行了研究.结果表明,随着氢稀释比增加,薄膜的晶化率明显提高,而氢稀释比过高时,薄膜晶化率呈现减少趋势.红外吸收光谱分析表明,纳米晶硅薄膜中氢的键合模式与薄膜的晶化特性密切相关.随着氢稀释比增加,薄膜中整体氢含量和SiH2键合密度明显减少,而在高氢稀释比条件下,氢稀释比增加导致薄膜中SiH2键合密度和整体氢含量增加.     

红外光谱法研究射频功率对微晶硅薄膜微结构的影响

采用射频等离子体增强化学气相沉积(RF-PECVD)技术,在硅衬底上以不同的射频功率生长微晶硅(μc-Si:H)薄膜,利用傅里叶变换红外透射光谱技术对薄膜进行测试.通过对红外透射光谱的高斯拟合分析,结果表明薄膜中的氢含量和硅氢键合模式跟射频功率密切相关;当射频率从30W增加到110W时,薄膜中的氢含量先减少后慢慢增加,而结构因子逐渐增加后再减小,并且硅氢键合模式由以SiH为主转变为以SiH2为主.并讨论了这些参量随射频功率变化的机理.     

衬底温度和硼掺杂对p型氢化微晶硅薄膜结构和电学特性的影响

以B₂H₆为掺杂剂,采用射频等离子体增强化学气相沉积技术在玻璃衬底上制备p型氢化微晶硅薄膜.研究了衬底温度和硼烷掺杂比对薄膜的微结构和暗电导率的影响.结果表明：在较高的衬底温度下很低的硼烷掺杂比即可导致薄膜非晶化;在实验范围内,随着衬底温度升高薄膜的晶化率单调下降,暗电导率先缓慢增加然后迅速下降,变化趋势与硼烷掺杂比的影响极为相似.最后着重讨论了p型氢化微晶硅薄膜的生长机理. 关键词： p型氢化微晶硅薄膜 衬底温度 晶化率 电导率     

氢稀释对纳米晶硅薄膜晶化特性的影响及薄膜生长机理

以SiH₄与H₂作为前驱气体,采用射频等离子增强化学气相沉积技术制备了纳米晶硅薄膜.利用Raman散射和红外吸收光谱等技术,对不同氢稀释比条件下薄膜的微观结构和键合特性进行了研究.结果表明,随着氢稀释比增加,薄膜的晶化率明显提高,而氢稀释比过高时,薄膜晶化率呈现减少趋势.红外吸收光谱分析表明,纳米晶硅薄膜中氢的键合模式与薄膜的晶化特性密切相关.随着氢稀释比增加,薄膜中整体氢含量和SiH₂键合密度明显减少,而在高氢稀释比条件下,氢稀释比增加导致薄膜中SiH₂键合密度和整体氢含量增加.     

激发频率对高氢稀释下纳米晶硅薄膜生长特性的影响

利用等离子体增强化学气相沉积技术,在高氢稀释条件下,研究不同激发频率对纳米晶硅薄膜生长特性的影响.剖面透射电子显微镜(TEM)分析结果显示,不同激发频率下制备的纳米晶硅薄膜晶化区均呈锥状结构生长,但13.56 MHz激发频率下制备的纳米晶硅薄膜最初生长阶段存在非晶态孵化层,即纳米晶硅薄膜的形成经历了由非晶态孵化层到晶态结构层的转变.而高激发频率(40.68 MHz)下硅纳米晶则能直接在非晶态衬底上生长形成.Raman谱和红外吸收谱测量结果表明高激发频率(40.68 MHz)下制备的纳米晶硅薄膜不但具有较高     

沉积温度对微晶硅薄膜结构特性的影响

采用PECVD技术，在玻璃衬底上沉积μc-Si:H薄膜. 用拉曼光谱、SEM和UV分光光度计对不同沉积温度下沉积的薄膜的结构特性进行分析. 研究发现：沉积温度较低时，随着沉积温度的升高，薄膜的晶化率增加；当沉积温度超过某一温度值时，随着温度的进一步升高，薄膜的晶化率降低. 这时，表面反应由表面扩散限制转变为流量控制. 该温度值随着硅烷含量的降低而降低. 关键词： 氢化微晶硅薄膜 拉曼散射谱 晶化率 UV分光光度计     

氮化硅薄膜中纳米非晶硅颗粒的键合结构及光致发光

采用螺旋波等离子体化学气相沉积技术以N₂/SiH₄/H₂为反应气体制备了镶嵌有纳米非晶硅颗粒的氢化氮化硅薄膜,通过改变N₂流量实现了薄膜从红到蓝绿的可调谐光致发光.傅里叶红外透射和紫外-可见光吸收特性分析表明,所生长薄膜具有较高的氢含量,N₂流量增加使氢的键合结构发生变化,非晶硅颗粒尺寸减小,所对应的薄膜的光学带隙逐渐增加和微观结构有序度减小.可调光致发光(PL)主要来源于纳米硅颗粒的量子限制效应发光,随N₂流量增加,PL的谱线展宽并逐渐增强. 关键词： 傅里叶红外透射谱 光吸收谱 纳米硅粒子镶嵌薄膜 光致发光     

Influence of deposition pressure on structural, optical and electrical properties of nc-Si:H films deposited by HW-CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were deposited using HW-CVD technique at various deposition pressures. Characterisation of these films from Raman spectroscopy revealed that nc-Si:H thin films consist of a mixture of two phases, crystalline phase and amorphous phase containing small Si crystals embedded therein. We observed increase in crystallinity in the films with increase in deposition pressure whereas the size of Si nanocrystals was found ∼2 nm over the entire range of deposition pressure studied. The FTIR spectroscopic analysis showed that with increasing deposition pressure the predominant hydrogen bonding in the films shifts from, Si-H to Si-H₂ and (Si-H₂)_n complexes and the hydrogen content in the films was found in the range 6.2-9.3 at% over the entire range of deposition pressure studied. The photo and dark conductivities results also indicate that the films deposited with increasing deposition pressure get structurally modified. It has been found that the optical energy gap range was between 1.72 and 2.1 eV with static refractive index between 2.85 and 3.24. From the present study it has been concluded that the deposition pressure is a key process parameter to induce the crystallinity in the Si:H thin films using HW-CVD.     

Growth characteristics of amorphous-layer-free nanocrystalline silicon films fabricated by very high frequency PECVD at 250 ℃

Amorphous-layer-free nanocrystalline silicon films were prepared by a very high frequency plasma enhanced chemical vapor deposition(PECVD) technique using hydrogen-diluted SiH4 at 250 C.The dependence of the crystallinity of the film on the hydrogen dilution ratio and the film thickness was investigated.Raman spectra show that the thickness of the initial amorphous incubation layer on silicon oxide gradually decreases with increasing hydrogen dilution ratio.High-resolution transmission electron microscopy reveals that the initial amorphous incubation layer can be completely eliminated at a hydrogen dilution ratio of 98%,which is lower than that needed for the growth of amorphous-layer-free nanocrystalline silicon using an excitation frequency of 13.56 MHz.More studies on the microstructure evolution of the initial amorphous incubation layer with hydrogen dilution ratios were performed using Fourier-transform infrared spectroscopy.It is suggested that the high hydrogen dilution,as well as the higher plasma excitation frequency,plays an important role in the formation of amorphous-layer-free nanocrystalline silicon films.     

Effects of high hydrogen dilution ratio on optical properties of hydrogenated nanocrystalline silicon thin films

Hydrogenated nanocrystalline silicon thin films were prepared by plasma enhanced vapor deposition technique. In our experiment, hydrogen dilution ratio R_H was changed mainly, while the other parameters, such as the radio frequency power, the direct current bias value, the chamber pressure, the total gas flow and the substrate temperature were kept constant. The film's surface topography was gained by AFM. The chemical bond was confirmed by Fourier transform infrared spectra. The optical properties were characterized by transmission spectra. To consider absorption peak of stretching vibration mode of SiH₃ at 2140 cm⁻¹ and to reduce the calculation error, a hydrogen content calculation method was proposed. Effects of hydrogen dilution ratio on the deposition rate v and hydrogen content C_H were investigated. The bonding mode and the force constants k of chemical bond, the structural factor f in films were changed by high hydrogen dilution ratio, which gave rise to the shift of absorption peak of infrared stretching mode and the decrease of optical band gap E_g.     

Influences of hydrogen dilution on microstructure and optical absorption characteristics of nc-SiO_x:H film

By using the plasma enhanced chemical vapor deposition(PECVD) technique, amorphous silicon oxide films containing nanocrystalline silicon grain(nc-Si O x:H) are deposited, and the bonding configurations and optical absorption properties of the films are investigated. The grain size can be well controlled by varying the hydrogen and oxygen content,and the largest size is obtained when the hydrogen dilution ratio R is 33. The results show that the crystallinity and the grain size of the film first increased and then decreased as R increased. The highest degree of crystallinity is obtained at R = 30.The analyses of bonding characteristics and light absorption characteristics show that the incorporation of hydrogen leads to an increase of overall bonding oxygen content in the film, and the film porosity first increases and then decreases. When R = 30, the film can be more compact, the optical absorption edge of the film is blue shifted, and the film has a lower activation energy.     

Features of the structure and defect states in hydrogenated polymorphous silicon films

The structural and electronic properties of thin hydrogenated polymorphous silicon films obtained by plasma-enhanced chemical vapor deposition from hydrogen (H₂) and monosilane (SiH₄) gas mixture have been studied by means of transmission electron microscopy, electron paramagnetic resonance (EPR) spectroscopy, and Raman spectroscopy. It has been established that the studied films consist of the amorphous phase containing silicon nanocrystalline inclusions with the average size on the order of 4–5 nm and the volume fraction of 10%. A signal was observed in the hydrogenated polymorphous silicon films during the EPR investigation that is attributed to the electrons trapped in the conduction band tail of microcrystalline silicon. It has been shown that the introduction of a small fraction of nanocrystals into the amorphous silicon films nonadditively changes the electronic properties of the material.     

Oriented Growth of Nanocrystalline Gamma Ferric Oxide in Electrophoretically Deposited Films

Films of nanocrystalline γ-Fe₂O₃ were deposited on silicon substrates by using the technique of electrophoretic deposition. The precursor powder was nanocrystalline γ-Fe₂O₃, which was synthesized, using DC arc plasma in the oxygen ambient by vapour–vapour interaction in gas phase condensation; at a stabilized arc current of 40 A. This powder was characterized by X-ray diffraction, Transmission Electron Microscopy, Vibrating Sample Magnetometer and Mössbauer Spectroscopy. An increase in directional coercivity was observed in case of films deposited on silicon substrates, which is dramatically significant. Preferred orientation of almost similar sized nanocrystalline magnetic domains in deposited films is evident from the results of X-ray diffraction and Transmission Electron Microscopy results. The preferred alignment of the nanocrystallites seems to be responsible for the significant changes observed in magnetic properties of films.     

Microstructure of hydrogenated silicon thin films prepared from silane diluted with hydrogen

We report results obtained from FTIR and TEM measurements carried out on silicon thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) from silane diluted with hydrogen. The hydrogen content, the microstructure factor, the mass density and the volume per Si-H vibrating dipoles were determined as a function of the hydrogen dilution. Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to microcrystalline hydrogenated silicon (μc-Si:H). With increasing dilution the transition from amorphous to microcrystalline phase appears faster and the average mass density of the films decreases. The μc-Si:H films are mixed-phase void-rich materials with changing triphasic volume fractions of crystalline and amorphous phases and voids. Different bonding configurations of vibrating Si-H dipoles were observed in the a-Si:H and μc-Si:H. The bonding of hydrogen to silicon in the void- and vacancy-dominated mechanisms of network formation is discussed.     

Low temperature plasma production of hydrogenated nanocrystalline silicon thin films

The hydrogenated nanocrystalline silicon (nc-Si:H) thin films were produced by capacitively-coupled plasma enhanced chemical vapor deposition (PECVD) technique at low substrate temperatures (T_s ≈ 40–200 °C). Firstly, for particular growth parameters, the lowest stable T_s was determined to avoid temperature fluctuations during the film deposition. The influence of the T_s on the structural and optical properties of the films was investigated by the Fourier transform infrared (FTIR), UV–visible transmittance/reflectance and X-ray diffraction (XRD) spectroscopies. Also, the films deposited at the center of the PECVD electrode and those around the edge of the PECVD electrode were compared within each deposition cycle. The XRD and UV–visible reflectance analyses reveal the nanocrystalline phase for the films grown at the edge at all T_s and for the center films only at 200 °C. The crystallinity fraction and lateral dark conductivity decrease with lowered T_s. FTIR analyses were used to track the hydrogen content, void fraction and amorphous matrix volume fraction within the films. The optical constants obtained from the UV–visible transmittance spectroscopy were correlated well with the FTIR results. Finally, the optimal T_s was concluded for the application of the produced nc-Si:H in silicon-based thin film devices on plastic substrates.