纳米硅薄膜的Raman光谱

通过等离子增强化学气相沉积法,制备了本征和掺磷的氢化纳米硅薄膜(nc-Si:H),研究了晶粒尺寸和掺杂浓度对纳米硅薄膜喇曼谱的影响.结果表明晶粒变小和掺杂浓度增加都使纳米晶粒的TO模峰位逐渐偏离声子限制模型的计算值.X射线衍射和高分辨电镜像的结果表明晶粒变小导致硅晶粒应力增加,而掺杂使晶粒内部杂质和缺陷增多,这些因素破坏了晶粒内晶格的平移对称性,进一步减小声子的平均自由程,导致实验值偏离理论计算值.晶格平移对称性的破缺还体现在,随晶粒尺寸减小或掺杂浓度增加,喇曼谱中TA、LA振动模的相对散射强度增加.     

晶粒尺寸分布对纳米晶硅薄膜喇曼散射谱的影响

用热丝助化学汽相反应法沉积了nc－Si：H薄膜，测量了它的喇曼散射谱，由透射电子显微镜直接测量了晶粒的大小和分布．应用声子强限制模型和球形粒子假设，并考虑到纳米晶粒的分布对样品的喇曼散射谱进行了拟合．结果表明，在考虑到纳米粒子的尺寸分布后，采用指数权重函数比采用高斯型权重函数更接近于实验测量的喇曼谱．     

应变对PbSe材料晶格振动的影响

在晶格失配的BaF2衬底上用分子束外延技术生长了不同厚度的PbSe单晶薄膜,PbSe外延薄膜的喇曼光谱测量到位于136～143cm-1之间的布里渊区中心纵光学声子(LO)振动,位于83～88cm-1之间的纵光学声子与横光学声子的耦合模(LO-TO)振动,以及位于268～280cm-1之间的2LO声子振动.而且PbSe薄膜的LO声子频率随薄膜厚度的不同明显移动,随着薄膜的厚度减小声子频率线性增大,这是由外延膜与衬底之间的失配应力不同引起的.为了理解PbSe声子振动模喇曼活性的物理原因,还比较分析了PbSe体单晶的喇曼光谱,同样,PbSe体单晶样品也呈现出喇曼活性的散射峰.     

应变对PbSe材料晶格振动的影响

在晶格失配的BaF2衬底上用分子束外延技术生长了不同厚度的PbSe单晶薄膜,PbSe外延薄膜的喇曼光谱测量到:位于136～143cm-1之间的布里渊区中心纵光学声子(LO)振动,位于83～88cm-1之间的纵光学声子与横光学声子的耦合模(LO-TO)振动,以及位于268～280cm-1之间的2LO声子振动.而且PbSe薄膜的LO声子频率随薄膜厚度的不同明显移动,随着薄膜的厚度减小声子频率线性增大,这是由外延膜与衬底之间的失配应力不同引起的.为了理解PbSe声子振动模喇曼活性的物理原因,还比较分析了PbSe体单晶的喇曼光谱,同样,PbSe体单晶样品也呈现出喇曼活性的散射峰.     

激光能量对沉积纳米Si薄膜晶粒尺寸的影响

为了制备纳米硅薄膜,采用脉冲激光沉积系统,保持靶材和衬底间距不变,在不同激光能量条件下,得到一系列纳米Si薄膜。利用喇曼散射光谱和X射线衍射谱对晶粒尺寸进行了计算和分析,取得了几组数据。结果表明,改变脉冲激光能量时,纳米Si晶粒平均尺寸均随能量的增强先增大后减小;在单脉冲能量为300mJ时制备的纳米Si晶粒平均尺寸最大,为8.58nm。这一结果对纳米硅薄膜制备的研究有积极意义。     

CdTe/ZnTe超晶格的多声子共振喇曼谱研究

用共振喇曼散射研究了CdTe/ZnTe应变层超晶格的多声子谱.实验结果表明,我们首次观察到了多达10级的ZnTeLO的多声子喇曼散射,和反映超晶格结构的子带跃迁介入多声子共振喇曼散射过程的实验现象.     

微量掺杂半导体材料晶格振动的光谱研究

在全频率范围内对照微量掺杂材料的红外吸收谱和喇曼散射谱,运用递推方法计算晶格振动的局部声子态密度,给出了金刚石结构半导体材料中晶格振动的普遍特征,在理论上定性定量地阐明了带内低频准局域模和带外高频定域模的物理涵义。     

掺Be分子束外延GaAs的喇曼光谱

利用喇曼光谱研究了掺Be分子束外延P型GaAs中晶格振动的纵光学声子LO与空穴等离子体激元的耦合.观测了耦合模L_+与L_-的喇曼光谱及其谱峰强度和位置随不同空穴浓度的变化,并对谱图进行了分析和讨论.     

n型和p型4H-SiC的二级喇曼谱

给出了n型和p型4H-SiC的二级喇曼谱的实验结果.指认了所观察到的一些光谱结构对应的特定声子支及其在布里渊区中相应的对称点.发现在4H-SiC的二级喇曼谱中存在能量差约为10cm-1的双谱线结构,这一结构与六方相GaN,ZnO和AlN的双谱线结构具有相同的能量差.二级喇曼谱的截止频率对于不同掺杂情况的4H-SiC具有相同的值.它并不等于n型掺杂4H-SiC的A1(LO)声子的倍频,而是等于未掺杂样品的A1(LO)声子的倍频.掺杂类型和杂质浓度对4H-SiC的二级喇曼谱几乎没有影响.     

n型和p型4H-SiC的二级喇曼谱

给出了n型和p型4H-SiC的二级喇曼谱的实验结果.指认了所观察到的一些光谱结构对应的特定声子支及其在布里渊区中相应的对称点.发现在4H-SiC的二级喇曼谱中存在能量差约为10cm-1 的双谱线结构,这一结构与六方相GaN,ZnO和AlN的双谱线结构具有相同的能量差.二级喇曼谱的截止频率对于不同掺杂情况的4H-SiC具有相同的值.它并不等于n型掺杂4H-SiC的A1(LO)声子的倍频,而是等于未掺杂样品的A1(LO)声子的倍频.掺杂类型和杂质浓度对4H-SiC的二级喇曼谱几乎没有影响.     

A quantitative model of the effect of grain size on the resistivity of polycrystalline silicon resistors

The effect of grain size on the resistivity of polycrystalline silicon films has been investigated theoretically and experimentally. It is shown that existing models do not accurately predict the resistivity dependence on doping concentration as grain size increases. A new modified trapping theory demonstrates from a good agreement with experimental results that a significant increase in grain size drastically reduces the sensitivity of polysilicon resistivity to doping concentration.     

集成电路中多晶硅薄膜载流子迁移率的实验研究和理论模型

本文系统地研究了多晶硅薄膜载流子迁移率与掺杂浓度的关系,发现不仅如前人所指出的那样,多晶硅载流子迁移率在中等掺杂区有一极小值,而且同时在高掺杂区存在一个极大值.本文将前人提出的杂质分凝模型、晶粒间界陷阱模型和杂质散射机构结合起来,从理论上计算了极大值及其相应的掺杂浓度与晶粒大小、晶粒间界界面态密度的关系,并与实验结果进行了比较.理论模型较好地说明了实验结果.     

Modeling and optimization of monolithic polycrystalline silicon resistors

The processing parameters of monolithic polycrystalline silicon resistors are examined, and the effect of grain size on the sensitivity of polysilicon resistivity versus doping concentration is studied theoretically and experimentally. Because existing models for polysilicon do not accurately predict resistivity dependence on doping concentration as grain size increases above 600 Å, a modified trapping model for polysilicon with different grain sizes and under various applied biases is introduced. Good agreement between theory and experiments demonstrates that an increase in grain size from 230 to 1220 Å drastically reduces the sensitivity of polysilicon resistivity to doping levels by two orders of magnitude. Such an increase is achieved by modifications of the integrated-circuit processes. Design criteria for the optimization of monolithic polysilicon resistors have also been established based on resistivity control, thermal properties, and device geometry.     

Characterization of stress in doped and undoped polycrystalline silicon before and after annealing or oxidation with laser raman spectroscopy

Stress in polycrystalline silicon (poly-Si) was characterized with laser Raman spectroscopy. Effects of diffusion of phosphorus, annealing and oxidation on stress were especially studied. Relaxation of undirectional stress by annealing and oxidation was observed. Undirectional stress was relaxed by heavy doping of phosphorus which made a grain size larger. Compressive stress increased, however, by oxidation in poly-Si with a smaller grain size.     

Physical Model for the Resistivity and Temperature Coefficient of Resistivity in Heavily Doped Polysilicon

One of the key benefits of using polysilicon as the material for resistors and piezoresistors is that the temperature coefficient of resistivity (TCR) can be tailored to be negative, zero, or positive by adjusting the doping concentration. This paper focuses on optimization of the boron doping of low-pressure chemical vapor deposited polysilicon resistors for obtaining near-zero TCR and development of a physical model that explains quantitatively all the results obtained in the optimization experiments encompassing the doping concentration ranges that show negative, near-zero, and positive TCR values in the polysilicon resistors. The proposed model considers single-crystal silicon grain in equilibrium with amorphous silicon grain boundary. The grain boundary carrier concentration is calculated considering exponential band tails in the density of states for amorphous silicon in the grain boundaries. Comparison of the results from the model shows excellent agreement with the measured values of resistivity as well as TCR for heavily doped polysilicon. It is shown that the trap density for holes in the grain boundary increases as the square root of the doping concentration, which is consistent with the defect compensation model of doping in the amorphous silicon grain boundaries.     

Laser forming of silicon films using nanoparticle precursor

Polycrystalline silicon films containing cubic silicon crystallites of size 3–4 μm have been formed on nickel substrates by fusing and sintering silicon nanoparticle precursors using a laser. A mechanism for the fusion and sintering of these nanoparticles, resulting in reduced heat input and continuous film formation by surface and grain boundary diffusion, is discussed. Films were characterized by optical microscopy, scanning electron microscopy, energydispersive spectroscopy, and Raman spectroscopy. Films were doped with n- as well as p-type dopants by using a laser doping technique and their current-voltage (I–V) characteristics were measured.     

Effect of doping concentration on the grain boundary trap density and threshold voltage of polycrystalline SOI MOSFETs

PolySOI MOSFETs have been fabricated on undoped and doped polycrystalline silicon films and characterized to study the effect of doping on grain boundary passivation. The grain boundary trap density (N_ST) and threshold voltages have been extracted experimentally to evaluate the extent of grain boundary passivation by the dopants. Charge sheet model based on the effective doping concentration has been employed to analytically estimate the threshold voltages using the experimentally determined grain boundary trap density and grain size (L_g) as model parameters. The variation of threshold voltages with increasing doping concentration for the range of N_A ? (N_ST/L_g) has been studied both by simulation and experiments and the results are presented. Analytically estimated threshold voltages and experimental results show that the threshold voltage falls with increase in the dopant concentration and that this effect is indeed due to the reduction in N_ST as a result of the grain boundary passivation by the dopants.     

Raman scattering in-depth evaluation of recrystallized silicon-on-oxide using different wavelength excitation

Recrystallized silicon-on-oxide were analyzed by laser Raman scattering spectroscopy. By changing the excitation laser wavelength, the in-depth stress profile was obtained. The in-depth stress change was strongly dependent on recrystallization power. Recrystallized silicon structures were confirmed by cross sectional TEM observations. Dependent on recrystallization power, silicon film structures changed from small grain or small and large two grain layers to continuous large grain films.     

Distributions of substitutional and interstitial impurities in silicon ingot with different grain morphologies

A multicrystalline silicon ingot with columnar and irregular grains was obtained from metallurgical-grade silicon (MG-Si) by directional solidification. The segregation behaviors of substitutional and interstitial impurities in different grain morphologies have been studied. The concentration distribution of substitutional impurities (B and Al) in the silicon ingot was accord with the Scheil's equation, which depended on the grain morphology. However, the concentration distribution of interstitial impurities (Fe, Ti, Cu, and Ni) was only accord with the Scheil's equation under the columnar grains growth condition. The difference lattice sites of the impurities will result in the disparate segregation behavior of impurities for columnar and irregular grains growth, which leads to the diverse concentration distribution of substitutional and interstitial impurities in the silicon ingot. Furthermore, the transport mechanism of interstitial and substitutional impurities in front of the solid-liquid interface boundary has been revealed.