热处理升温快慢对非晶硅中形成的纳米硅粒尺寸的影响

含氢非晶硅薄膜经过快速热退火处理后,我们用拉曼散射和X-射线衍射技术对样品进行分析.我们的实验结果表明:在非晶硅薄膜中形成的纳米硅晶粒的大小随着热退火过程中升温快慢而变化.在升温过程中,当单位时间内温度变化量较大时（～100℃/s）,则所形成纳米硅粒较小（～1.6～15nm）;若单位时间内温度变化量较低（～1℃/s）,则纳米硅粒较大（～23～46nm）。根据分形生长理论和计算机模拟,我们讨论了升温快慢与所形成的纳米硅颗粒大小的关系.     

低温高速率沉积非晶硅薄膜及太阳电池

采用射频等离子体增强化学气相沉积(RF-PECVD)技术,保持沉积温度在125℃制备非晶硅薄膜材料及太阳电池。在85 Pa的低压下以及400～667 Pa的高压下,改变Si H4浓度和辉光功率等沉积参数,对本征a-Si材料的性能进行优化。结果表明,在高压下,合适的Si H4浓度和压力功率比可以使a-Si材料的光电特性得到优化,并且薄膜的沉积速率得到一定程度的提高。采用低压低速和高压高速的沉积条件,在125℃的低温条件下制备出效率为6.7%的单结a-Si电池,高压下本征层a-Si材料的沉积速率由0.06～0.08 nm/s提高到0.17～0.19 nm/s。     

柔性衬底硅基太阳电池ZAO透明导电膜的研究

采用孪生对靶直流磁控溅射的方法,在室温下制备了ZnO:Al(ZAO)薄膜材料,将其应用于柔性衬底非晶硅薄膜太阳电池的窗口电极。通过调整Ar气流量(1.67×10-7 m3/s～8.33×10-7 m3/s),优化了ZAO薄膜的结构、成份及光电性能。得到如下结论:理想的Ar气流量为3.33×10-7 m3/s,此时ZAO薄膜具有较高的晶化率和C轴择优取向,薄膜的霍尔电阻率达为4.26×10-4Ω.cm,载流子浓度达到1.8×1021cm-3,可见光波长范围内的光学透过率达到85%以上。将优化后的ZAO薄膜用于柔性衬底非晶硅薄膜太阳电池的窗口电极,转化效率达到了4.26%。     

The effects of hydrogen on aluminum-induced crystallization of sputtered hydrogenated amorphous silicon

The effects of hydrogen on aluminum-induced crystallization (AIC) of sputtered hydrogenated amorphous silicon (a-Si:H) were investigated by controlling the hydrogen content of a-SiH films. Nonhydrogenated (a-Si) and hydrogenated (a-Si:H) samples were deposited by sputtering and plasma-enhanced chemical vapor deposition (PECVD). All aluminum films were deposited by sputtering. Hydrogen was introduced into the sputter-deposited a-Si films during the deposition. After deposition, the samples were annealed at temperatures from 200°C to 400°C for different periods of time. X-ray diffraction (XRD) patterns were used to confirm the presence and degree of crystallization in the a-Si:H films. For nonhydrogenated films, crystallization initiates at a temperature of 350°C. The crystallization of sputter-deposited a-Si:H initiates at 225°C when 14% hydrogen is present in the film. As the hydrogen content is decreased, the crystallization temperature increases. On the other hand, the crystallization initiation temperature for PECVD a-Si:H containing 11at.%H is 200°C. Further study revealed that the crystallization initiation temperature is a function, not only of the total atomic percent hydrogen in the film, but also a function of the way in which the hydrogen is bonded in the film. Models are developed for crystallization initiation temperature dependence on hydrogen concentration in a-Si:H thin films.     

Study of thermal equilibration in selenium- and sulphur-doped a-Si:H

The present paper reports the thermal equilibration in selenium- and sulphur-doped hydrogenated amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition. The conductivity of Se- and S-doped a-Si:H is observed to be very sensitive to the rate at which the samples are cooled following the high temperature anneal. Arrhenius plots of conductivity for various doped films revealed thermal equilibration above the equilibration temperature, T _E, thus accounting for larger activation energies. The barrier energy is lower for a-Si,Se:H than for a-Si,S:H, due to a higher defect density in S-doped films.     

On the essence of the high photosensitivity of a-Si:H layered films

It is established that layered a-Si:H films grown by cyclic deposition with by-layer annealing in hydrogen plasma are characterized by high photosensitivity, which, at room temperature, exceeds by more than an order of magnitude the photosensitivity of regular nondoped a-Si:H films grown by deposition in the plasma of an HF glowing discharge. The high photosensitivity is determined by small dark conductance and the high photoconductance of layered films in the range of room temperature. It is demonstrated that this can be stipulated by the existence of sensitizing levels, related with higher oxygen concentrations at layer’s interface and the low concentration of broken silicon bonds in the depth of layers with a more ordered structure.     

Microstructure evolution of amorphous silicon thin films upon annealing studied by positron annihilation

Amorphous silicon (a-Si) thin films were prepared on glass substrates by plasma enhanced chemical vapor deposition (PECVD). Influence of annealing temperature on the microstructure, surface morphology, and defects evolution of the films were studied by X-ray diffraction (XRD), atomic force microscope (AFM) and positron annihilation Doppler broadening spectroscopy (DBS) based on a slow positron beam, respectively. The S parameter of the as-deposited a-Si thin film is high, indicative of amorphous state of Si film with many defects. The a-Si gradually grows into polycrystalline silicon with increasing temperature to 650 °C. For the films annealed below ~450 °C, positron diffusion lengths are rather small because most positrons are trapped in the defects of the a-Si films and annihilated there. With further rising the temperature to 600 °C, the diffusion length of positrons increases significantly due to the removal of vacancy-type defects upon annealing at a high temperature. The results indicate that the coalescence of small vacancy-type defects in a-Si thin film and the crystallization of a-Si occur around 450 °C and 650 °C, respectively.     

Study of photoconductivity and persistent photoconductivity in sulphur-doped amorphous hydrogenated silicon

We report on the spectral response and intensity dependence of photoconductivity (PC) and persistent photoconductivity (PPC) in plasma-enhanced chemical vapour deposition grown sulphur-doped n-type a-Si:H films. From the intensity dependence of PC it is found that the addition of sulphur changes the recombination mechanism from monomolecular for intrinsic and low-doped films to bimolecular at a high sulphur doping level. The photo-induced metastable increase of dark conductivity in these films is found to be quite similar to that for compensated and doping-modulated a-Si:H films. The PPC effect is detectable up to an illumination temperature of at least 380 K the highest temperature used in this study. At 300 K the conduction persists at a level of one order higher than the equilibrium dark conductivity for over 10³ s after removing the excitation. The PPC in a-Si, S:H is explained in terms of the valence alternation pair model.     

Deposition and crystallization of a-Si thin films by rapid thermal processing

The deposition and crystallization of a-Si thin films grown by rapid thermal processing have been studied, using transmission electron microscopy. The a-Si films were deposited in a rapid thermal processor at reduced pressures in the temperature range of 530–580°C, at different deposition pressures and silane flow rates and subsequently were annealed in-situ by high temperature rapid thermal annealing (RTA) or by a two-step annealing process involving low temperature furnace annealing (FA) followed by high temperature RTA. The activation energy of a-Si deposition was found to be approximately 1.7 eV, in reasonable agreement with the conventional LPCVD technique. It has been found that the deposition temperature and deposition rate have a strong effect on the grain size, which is attributed to the nucleation processes in the bulk of the films. The combination of low deposition temperature, high deposition rate and a two-step annealing process permits the low temperature growth of poly-Si films of 100 nm thickness, with large grains of 520 nm size, containing a low density of microtwins and characterized by very low surface roughness of 2.2 nm.     

非晶硅Pin二极管的1MeV电子幅照效应

本文报道a-Si∶H本征膜及Pin二极管的1MeV1.4×10¹⁵,4.2×10¹⁵,8.4×10¹⁵/cm²电子幅照实验结果和退火行为.测量了电子辐照对a-Si∶H光暗电导率和光致发光谱的影响,以及a-Si∶H Pin二极管光伏特性和光谱响应随电子辐照剂量的变化.发现电子辐照在a-Si∶H本征膜和二极管中引起严重的损伤,和二极管光谱响应的峰值"红移".但未见饱和现象,还观测到明显的室温恢复现象;但高温退火处理后未能完全恢复.本文对以上实验结果给出了合理的解释.     

直流磁控溅射制备a-Si:H膜工艺及其在激光器腔面膜上的应用

利用直流(DC)磁控溅射方法制备氢化非晶硅(a-Si∶H)薄膜。研究了氢气流量、溅射源功率对膜的沉积速率、氢含量(CH)以及光学性能的影响。通过傅里叶变换红外(FTIR)吸收光谱计算氢含量,其最大原子数分数为11%。用椭偏仪测量了膜的折射率n和消光系数k,发现a-Si∶H薄膜的k值和n值都随CH的增加而减小。将优化的实验结果用于半导体激光器腔面高反镜的镀制,a-Si∶H薄膜在808 nm波长处的n和k分别为3.2和8×10-3,获得了良好的激光输出特性。     

Size Control of Nanoscale Silicon Particles Formed in Thermally Annealed A-Si∶H Films and Its Photoluminescence

A method to control the si ze of nanoscale silicon grown in thermally annealed hydrogenated amorphous silico n (a-Si∶H) films is reported. Using the characterizing techniques of micro-Ra man scattering, X-ray diffraction and computer simulation, it is found that the sizes of the formed silicon particles change with the temperature rising rate i n thermally annealing the a-Si∶H films. When the a-Si∶H films have been anne aled with high rising rate( ~100 ℃/s), the sizes of nanoscale silicon particle s are in the range of 1.6~15 nm. On the other hand, if the a-Si∶H films have been annealed with low temperature rising rate(~1 ℃/s), the sizes of nanoscale silicon particles are in the range of 23~46 nm. Based on the theory of crystal nucleation and growth, the effect of temperature rising rate on the sizes of th e formed silicon particles is discussed. Under high power laser irradiation, in situ nanocrystallization and subsequent nc-Si clusters are small enough for vis ible light emission, authors have not detected any visible photoluminescence(PL) from these nc-Si clusters before surface passivation. After electrochemical ox idization in hydrofluoric acid, however, intense red PL has been detected. Cycli c hydrofluoric oxidization and air exposure can cause subsequent blue shift in t he red emission. The importance of surface passivation and quantum confinement i n the visible emissions has been discussed.     

Size Control of Nanoscale Silicon Particles Formed in Thermally Annealed A- Si: H Films and Its Photoluminescence

A method to control the size of nanoscale silicon grown in thermally annealed hydrogenated amorphous silicon (a-Si : H) films is reported. Using the characterizing techniques of micro-Raman scattering,X-ray diffraction and computer simulation, it is found that the sizes of the formed silicon particles change with the temperature rising rate in thermally annealing the a-Si : H films. When the a-Si: H films have been annealed with high rising rate( ～ 100 C/s), the sizes of nanoscale silicon particles are in the range of 1.6～ 15nm. On the other hand, if the a-Si: H films have been annealed with low temperature rising rate(～1 C/s),the sizes of nanoscale silicon particles are in the range of 23～46 nm. Based on the theory of crystal nucleation and growth, the effect of temperature rising rate on the sizes of the formed silicon particles is discussed. Under high power laser irradiation, in situ nanocrystallization and subsequent nc-Si clusters are small enough for visible light emission, authors have not detected any visible photoluminescence(PL) from these nc-Si clusters before surface passivation. After electrochemical oxidization in hydrofluoric acid, however, intense red PL has been detected. Cyclic hydrofluoric oxidization and air exposure can cause subsequent blue shift in the red emission. The importance of surface passivation and quantum confinement in the visible emissions has been discussed.     

隔热结构中非晶硅的释H_2机理与工艺研究

对采用等离子增强化学气相淀积法(PECVD)制备的氢化非晶硅(a-Si:H)薄膜进行了退火释H2实验,并对三文治结构膜层生长工艺作了改进。红外透射光谱表明:提高退火温度及增加退火时间会造成Si-H键断裂释放H2影响器件结构完整;不断改进设计,最终采用精简有效热敏面积及将退火工艺提前以扩张释H2渠道的方案,获得600℃退火后仍保持完整三文治结构的优化设计流程。     

快速光热退火法制备多晶硅薄膜的研究

为了制备应用于太阳电池的优质多晶硅薄膜,研究了非晶硅薄膜的快速光热退火技术。先利用 PECVD 设备沉积非晶硅薄膜,然后放入快速光热退火炉中进行退火。退火前后的薄膜利用 X 射线衍射仪(XRD)和扫描电子显微镜(SEM)测试其晶体结构及表面形貌,用电导率设备测试其暗电导率。研究表明退火温度、退火时间对非晶硅薄膜的晶化都有很大的影响,光热退火前先用常规高温炉预热有助于增大多晶硅薄膜的晶粒尺寸和暗电导率。     

非晶硅光电导层交流电阻率的研究

利用等效电路,估算出高性能液晶光阀对非晶硅光电导层交流电阻率的要求。用化学气相沉积法在最佳工艺条件下制备了非晶硅薄膜,测量了样品的交流电阻率。结果表明,非晶硅薄膜的交流电阻率随照射光的波长增大而先减小后增大,随功率密度、衬底温度和射频功率的增大而减小。样品的交流电阻率满足高性能液晶光阀光电导层的要求。     

Ion beam synthesis of low resistivity contacts in amorphous silicon-based materials

Low resistivity layers have been formed at low process temperatures, by high dose Co⁺ ion implantation in to hydrogenated amorphous silicon (a-Si:H) and amorphous silicon carbide (a-SiC:H). The lowest resistivities, of the order of 10 ohms/Sq, have been observed for the carbon-free films (a-Si:H) and can be obtained at annealing temperatures of <250°C. Schottky barrier contacts to the a-Si:H films exhibit near ideal behavior with low leakage currents, of the order 10⁻⁹ A·cm⁻². The electrical properties of the amorphous films are assessed as a function of ion dose, dose rate and annealing conditions, with a view to optimizing these parameters.     

衬底温度对超声喷雾法制备大面积绒面SnO_2:F薄膜特性影响的研究

详细研究了衬底温度对超声喷雾热分解工艺制备的大面积绒面SnO2:F薄膜的影响和薄膜微结构与薄膜电学、光学性能之间的关系。试验曲线和SEM图的研究结果表明,将衬底温度从370℃提高到470℃以上薄膜结晶程度大大提高,晶粒尺寸明显增大;温度在470℃左右绒度达到13%。文章同时对超声喷雾热分解工艺制备大面积绒面SnO2:F薄膜做了工艺探索,并将实验制得的薄膜用于制备非晶硅薄膜电池,其效率达到了6.46%。     

a-SiH 热处理过程中纳米硅粒尺寸的控制(英文)

报道了控制热处理过程中含氢非晶硅中纳米硅颗粒大小的一种新方法。用喇曼散射、X射线衍射和计算机模拟,发现在非晶硅中所形成的纳米硅颗粒的大小,随着热退火过程中升温速率的变化而变化。在退火过程中,若非晶硅薄膜升温速率较高(～100℃/s),则所形成纳米硅粒的大小在1.6～15nm;若非晶硅薄膜升温速率较低(～1℃/s),则纳米硅粒大小在23～46nm。根据晶体生长理论,讨论了升温速率的高低与所形成的纳米硅颗粒大小的关系。     

The process window of a-Si/Ti bilayer metallization for anoxidation-resistant and self-aligned TiSi2 process

The dependences of both oxidation-resistant and self-aligned silicidation properties on the thicknesses of top amorphous-Si (a-Si) and Ti metal in an a-Si/Ti bilayer process are presented. It is shown that a thin silicide layer formed during the reaction between a-Si and Ti films becomes a stable oxidation and nitridation barrier for oxygen- and nitrogen-related impurities. Moreover, the formation sequence of the silicide phase depends not only on the annealing temperature but also on the thickness of the Ti film. In addition, the preferential orientation of the silicide phase after annealing at high temperature also shows a strong dependence on the thickness of Ti film, which is attributed to the difference of the grain size in the polycrystalline silicide film. The allowed process window for the a-Si thickness can be determined experimentally and a reproducible and homogeneous self-aligned TiSi₂ film can be easily obtained by using the a-Si/Ti bilayer process in salicide applications despite high-level contaminations of oxygen impurities in both the as-deposited Ti film and the annealing ambient