纳米硅薄膜的低温电输运机制

在很宽的温度范围(500—20K)研究了本征和不同掺磷浓度的纳米硅薄膜的电输运现象.发现 原先的异质结量子点隧穿(HQD)模型能很好地解释薄膜在高温下(500—200K)的电导曲线,但 明显偏离低温下的实验值.低温电导(100—20K)具有单一的激活能W,并与k_BT值 大小相当(W～1—3k_BT),呈现出Hopping电导的特征.对HQD模型做了修正,认为 纳米硅同时存在两种输运机制：热激发辅助的电子隧穿和费米能级附近定域态之间的Hoppin g电导.高温时(T 关键词： 纳米硅薄膜 低温电导 电输运     

纳米硅薄膜退火特性

对使用等离子体增强化学汽相沉积(PECVD)法在不同淀积条件下制备的非晶硅(a-Si:H)、微晶硅(μc-Si:H)和纳米硅(nc-Si:H)薄膜在200—600℃温度范围进行常规退火研究。用共振核反应技术测量了样品中氢含量C_H值及退火对氢含量及其分布的影响。通过室温下对暗电导率的测量得到退火对nc-si:H薄膜电导率的影响,并与a-Si:H,μc-Si:H薄膜的退火行为作了比较。使用紫外/可见/近红外分光光度计对样品透射率进行了测量,分析计算得到了退火温度T_a与ac-Si:H薄膜光学带隙E_g~(o 关键词：     

氢化非晶硅的低温输运

从低温跳跃电导模型出发,计算低温下的跳跃频率,热发射率及输运能级随温度变化,分析讨论了非晶硅热激电导的低温峰。认为输运机制的变化是氢化非晶硅热激电导低温峰T_M独立于起始温度T₀的主要原因,T_M相应于输运机制变化的温度。 关键词：     

利用快速退火法从非晶硅薄膜中生长纳米硅晶粒

报道了一种从非晶硅薄膜中生长纳米硅晶粒的方法。含氢非晶硅薄膜经过快速热退火处理后，用拉曼散射和X射线衍射技术对样品进行分析。实验结果表明：纳米硅晶粒不但能在非晶硅薄膜中形成，而且所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，若单位时间内温度变化量较大（－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）。根据晶体生长理论和计算机模拟，讨论了升温快慢与所形成的纳米硅颗粒大小的关系。     

退火α—Ge／Cu叠层膜中输运性质的反常

本研究了退火α－Ｇｅ／Ｃｕ（α－Ｇｅ是非晶体态Ｇｅ）叠层中输运性质，获得以下新的结果：（１）α－Ｇｅ／Ｃｕ室温电阻Ｒ３００Ｋ与退火温度Ｔα之间关系出现反常；（２）α－Ｇｅ／Ｃｕ在退火过程中既出现互扩散，又存在固相反应和多相晶化；（３）实验首次发现在α－Ｇｅ／Ｃｕ膜中的分形现象，相应于分形结构，电阻率出现极小。     

TiO薄膜的制备及电输运性质

利用磁控溅射技术,通过改变氧分压在MgO (001)单晶基片上外延生长了一系列TiO薄膜,并对薄膜的结构、价态和电输运性质进行了系统研究. X射线衍射结果表明,所制备的薄膜具有岩盐结构,沿[001]晶向外延生长. X射线光电子能谱结果表明,薄膜中Ti元素主要以二价形式存在.所有样品均具有负的电阻温度系数,高氧分压下制备的薄膜表现出绝缘体的导电性质,低温下电阻与温度的关系遵从变程跳跃导电规律.低氧分压下制备的薄膜具有金属导电性质,并具有超导电性,超导转变温度最高可达3.05 K.所有样品均具有较高的载流子浓度,随着氧分压的降低,薄膜的载流子类型由电子主导转变为空穴主导.氧含量的降低可能加强了TiO中Ti—Ti键的作用,从而使低氧分压下制备的样品显现出与金属Ti相似的电输运性质,薄膜超导转变温度的提升可能与晶体结构或电子结构突变相关联.     

Rb3C60超导薄膜的电输运性质

在成功制备Ｃ６０外延薄膜的基础上，我们又尝试了碱金属Ｒｂ对该膜的掺杂。结果表明，从室温至８０Ｋ左右，Ｒｂ３Ｃ６０薄膜的电阻温度系数大于０，并近似符合公式：ρ（Ｔ）＝ａ＋ｂＴ＾２，与单晶样品一致。但是，当温度低于８０Ｋ以后，出现了弱的对数局域。在５Ｋ、零场下，样品的Ｊｃ值一般为１０＾３－１０＾４Ａ／ｃｍ＾２，且有如下规律：Ｊｃ（Ｔ）＝Ｊｃ（０）（１－Ｔ／Ｔｃ）＾ａ，α＝１．３－２．０。此外，我们还测     

SiOx∶H(0＜x＜2)薄膜光致发光的退火行为研究

采用退火后处理的方法，使SiO_x∶H(0＜x＜2)形成纳米硅与二氧化硅的镶嵌结构.利用红外透射谱、Raman谱和光致发光谱，系统地研究了不同退火温度对薄膜微结构及室温光致发光谱的影响.发现发光谱均由两个Gauss线组成，其中主峰随着退火温度的升高而红移，而位于835nm的伴峰不变.指出退火前在720—610nm的波长范围内强的主峰可能来源于膜中的非晶硅原子团，随退火温度的升高主峰的红移是由于非晶硅原子团的长大.而伴峰可能来自硅过剩或氧欠缺引入的某种发光缺陷.1170℃退火后在850n 关键词：     

a—Si：O：H薄膜微结构及其高温退火行为研究

以微区Raman散射、X射线光电子能谱和红外吸收对等离子体增强化学气相沉积（PECVD）法制备的氢化非晶硅氧（a-Si:O:H)薄膜微结构及其退火行为进行了细致研究。结果表明a-Si:O:H薄膜具有明显的相分离结构,富Si相镶嵌于富O相之中,其中富Si相为非氢化四面体结构形式的非晶硅（a-Si),富O相为Si,O,H三种原子随机键合形成的SiOx:H(x≈1.35)。经1150℃高温退火,薄膜中的H全部释出;SiOx:H(x≈1.35)介质在析出部分Si原子的同时发生结构相变,形成稳定的SiO2和SiOx(x≈0.64);在析出的Si原子参与下,薄膜中a-Si颗粒固相晶化的成核和生长过程得以进行,形成纳米晶硅（nc-Si),研究发现此时的薄膜具有典型的壳层结构,在nc-Si颗粒表面和外围SiO2介质之间存在着纳米厚度的SiOx(x≈0.64)中间相。     

硅纳米结点电子输运性质的计算

运用第一性原理密度泛函理论结合非平衡格林函数方法,对3个Si原子构成的直线链耦合在Au(100)面形成的三明治结构的纳米结点的电子输运进行计算.结果得到结点电导随距离的变化,当d_z=1.584 nm时,结合能最小,结构最稳定,此时Si-Si键长为0.216 nm,Si-Au键长为0.227 nm,电导为0.729 G₀(G₀=2e²/h),其电子传输通道主要由Si原子的p_x、p_y轨道电子构成;随着外电压的增大,结点的电导减小,而其I-V曲线表现出线性特征.     

Structural and optical properties of amorphous hydrogenated silicon carbonitride films produced by PECVD

Amorphous hydrogenated silicon carbonitride thin films (a-Si:C:N:H), deposited by plasma enhanced chemical vapour deposition (PECVD) using hexamethyldisilazane (HMDSN) as monomer and Ar as feed gas, have been investigated for their structural and optical properties as a function of the deposition RF plasma power, in the range of 100-300 W. The films have been analysed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis-NIR spectrophotometry and atomic force microscopy (AFM). From the analysis of the FT-IR spectra it results that the films become more amorphous and inorganic as RF plasma power increases. The incorporation of oxygen in the deposited layers, mainly due to the atmospheric attack, has been evaluated by XPS and FT-IR spectroscopy. Reflectance/transmittance spectra, acquired in the range of 200-2500 nm, allow to descrive the film absorption edge for interband transitions. A relationship between the optical energy band gap, deduced from the absorption coefficient curve, and the deposition RF plasma power has been investigated. The reduction of the optical energy gap from 3.85 to 3.69 eV and the broadening of the optical absorption tail with RF plasma power increasing from 100 to 300 W are ascribed to the growth of structural disorder, while the increase of the refractive index, evaluated at 630 nm, is attributed to a slight densification of the film. The AFM analysis confirms the amorphous character of the films and shows how the deposited layers become rougher when RF plasma power increases. The wettability of the film has been studied and related to the chemical composition and to the morphology of the deposited layers.     

利用光声光谱研究掺硫非晶硅薄膜的吸收特性

本文考虑到薄膜样品表面的多次反射,从理论上推导了光声信号的表达式.对α-Si:H薄膜和掺硫α-Si:H薄膜随入射光波长变化的吸收系数曲线进行了测定,并获得了光学带隙与掺硫浓度的关系.     

Study on stability of hydrogenated amorphous silicon films

Hydrogenated amorphous silicon （a-Si：H） films with high and same order of magnitude photosensitivity （-10^5） but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content （CH） as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si：H films. We used hydrogen elimination model to explain our experimental results.     

Influence of atomic hydrogen annealing on the optical properties of vacuum-deposited a-Si:H films

The influence of atomic hydrogen annealing on the optical parameters of a-Si:H films was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200-3000 nm. In this annealing, the deposition of a thin layer and treatment with atomic hydrogen were repeated alternately, where the thickness of the thin cyclic layer, d_cyc, and the treatment time of each cycle, t_ca, were kept fixed for each sample. A series of different samples with average thickness of 0.5 μm and different d_cyc and t_ca were prepared. It was found that the refractive index, n, and the optical energy gap, E_g, increase as the treatment time, t_ca, increases from 0 to 60 s, while at t_ca=120 s both n and E_g decrease. Also, both the refractive index and the optical energy gap decrease with increasing the relative diffusion length of hydrogen, √t_ca/d_cyc from 0.39 to 0.77. The widening of E_g is due to the structural relaxation resulting from impingement of atomic hydrogen on the growing surface. Thus, a good-quality a-Si:H with Urbach parameter 65 mev and optical energy gap of 1.78 eV was successfully prepared.     

Structural evolution of a-Si:H/SiO2 multilayers upon step by step thermal annealing

a-Si:H/SiO_2 multilayers were prepared by alternatively changing plasma enhanced chemical vapour deposition of a-Si:H layers and in situ plasma oxidation process. Subsequently, as-grown samples were annealed at temperatures from 350℃ to 1100℃ in N_2 ambient with an increment of 100℃. The evolution of bonding configurations and structures with annealing treatments was systematically investigated by Fourier-transform infrared spectroscopy. The peak position of Si－O stretching vibration of SiO_2 layers shift to 1087cm^{-1} after annealing at 1100℃, which demonstrates that the SiO_2 films fabricated by plasma oxidation after high temperature annealing can have similar properties to the thermal grown ones. A Si－O vibration from interfacial SiO_x was identified: the value x was found to increase as increasing the annealing temperature, which is ascribed to the cooperation of hydrogen effusion and reordering of the oxygen bond in SiO_x networks. The H-related bonds were observed in the form of H－Si－O_3 and H－Si－Si_{3-n}O_n (n=1－2) configurations, which are supposed to be present in SiO_2 and interfacial SiO_x layers, respectively. The H atoms bonded in different bonding configurations effuse at different temperatures due to their different desorption energies.     

铝诱导非晶硅薄膜的场致低温快速晶化及其结构表征

铝诱导非晶硅薄膜晶化可以降低退火温度、缩短退火时间，是制备多晶硅薄膜的一种重要方法.在此基础上，通过在退火过程中加入电场加速了界面处硅、铝原子间的互扩散，实现了非晶硅薄膜的快速低温晶化.实验结果表明，外加电场，退火温度为400℃，退火时间为60min时，薄膜的晶化率大于60％；退火温度为450℃退火时间为30min时，薄膜已经呈现明显的晶化现象；退火温度为500℃退火时间为15min时，薄膜的x射线多晶峰强度与非晶峰强度之比为未加电场的3—4倍. 关键词： 非晶硅薄膜 多晶硅薄膜 外加电场     

Dynamical resolidification behavior of silicon thin films during frontside and backside excimer laser annealing

Excimer laser annealing (ELA) is frequently employed to fabricate low-temperature polycrystalline silicon films on glass substrate. The grain size and crystallinity of polycrystalline silicon films are significantly affected by the resolidification behavior during ELA. A real-time in situ time-resolved optical measurement system is developed to record the rapid phase transformation process during ELA. The average solidification velocity of liquid-Si is calculated from these optical spectra using MATLAB and Excel softwares. Field emission scanning electron microscopy images reveal maximum grain size of poly-Si films with a diameter of 1 μm, which is obtained in the complete melting regime of both frontside ELA and backside ELA. Recrystallization mechanisms of complete melting of Si thin films in frontside ELA and backside ELA are demonstrated. Resolidification scenarios of partial melting, near-complete melting and complete melting in frontside ELA and backside ELA are proposed.     

Effect of annealing on the optical and electrical properties of ZnO:Er films

The effect of dopant concentration and annealing in the oxidizing atmosphere on the structural, optical, and electrical properties of ZnO:Er films deposited on sapphire substrates by the electron-beam evaporation method is investigated. The optical and electrical properties of these films were studied by UV-VIS-IR absorption and reflection spectroscopy, photoluminescence, and resistivity measurements. Experimental results reveal that as-deposited ZnO:Er films have both high transmittance in the visible range and low electrical resistivity and can be used as efficient transparent conducting oxides (TCOs). These films annealed in the oxidizing atmosphere have a visible emission band which can be used to fabricate light-emitting diodes.     

用H-W-ECR CVD系统实现氢化非晶硅薄膜在氢气环境下同时进行化学热退火和光诱导退火的研究

为了研究氢化非晶硅薄膜的稳定性，我们设计了一个在原子氢气氛中热退火的同时进行光诱导退火的实验(TLAH)。实验装置是由传统的微波电子回旋共振化学气相沉积系统改造而成为热丝辅助微波电子回旋共振化学气相沉积系统。为了对这一退火方法进行比较，对样品还进行了热退火、热退火同时进行光诱导退火。同时，为了定量地分析光电导衰退，我们假设光电导衰退遵循扩展指数规律：1/σph=1/σs-(1/σs-1/σ0)exp[-(t/τ)β]，这里扩展指数参数β 和时间常数 τ 可从与 lnt 的线性关系中截距和斜率得到, 式中光电导饱和值σs可以通过在对数坐标系中表示的光电导和光照时间关系进行高斯拟合得到。实验结果显示：TLAH 方法可以提高氢化非晶硅薄膜的稳定性、改善其微结构和光电特性，同时还发现，光学带隙明显减小、荧光光谱显著地朝着低能方向移动。     

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (E_d) and the annealing temperature were varied from 123 to 242 mJ/cm² and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d ≥ 188 mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.