FTIR研究快中子辐照直拉硅中的VO2

快中子辐照直拉硅(CZ-Si)经400-450℃热处理后，空位-双氧复合体(VO2)是其主要的缺陷．在300-500℃热处理快中子辐照的CZ-Si后，IR光谱中有919．6cm^-1和1006cm^-1两个吸收峰伴随VO2(889cm^-1)出现，这两个IR吸收峰是VO2的一种亚稳态缺陷(O-V-O)引起的，此缺陷态是由一个VO(A中心)与次临近的一个间隙氧原子(Oi)相互作用所形成的．在300℃延长退火时间或升高退火温度，都会使(O-V-O)转变为稳态VO2．辐照剂量在10^19数量级，经400-450℃热处理所形成的缺陷主要为多空位型，而VO2被抑制．     

直拉硅单晶原生漩涡缺陷的研究

本文用化学腐蚀方法,从含有漩涡缺陷的原生CZ硅单晶中分离出尺寸在1000—6000?间的氧沉淀,制成萃取复型样品,用TEM对氧沉淀作微区电子衍射分析。同时,观察硅薄膜中漩涡缺陷的TEM象,确定了二者的对应关系。结果表明,构成漩涡缺陷的氧沉淀主要是呈方形片的热液石英(keatite,silicak)及少量呈六角片的α方英石(α-cristobalite),沉淀片周边沿<110>方向,惯习面前者的为{100},后者的为{111}。样品的红外吸收光谱表明,方片状热液石英沉淀可能与1224cm^-1吸收峰相对应。 关键词：     

直拉硅单晶原生漩涡缺陷的研究

本文用化学腐蚀方法, 从含有漩涡缺陷的原生CZ硅单晶中分离出尺寸在1000--6000埃间的氧沉淀, 制成萃取复型样品,用T E M 对氧沉淀作微区电子衍射分析. 同时, 观察硅薄膜中漩涡缺陷的TEM 象, 确定了二者的对应关系. 结果表明, 构成漩涡缺陷的氧沉淀主要是呈方形片的热液石英(keatite, siliea k) 及少量呈六角片的。方英石(a-cristobalite ), 沉淀片周边沿<1 1 0> 方向, 惯习面前者的为{ 100} , 后者的为{ 1 1 1}. 样品的红外吸收光谱表明, 方片状热液石英沉淀可能与1 2 2 4 (1/cm ), 吸收峰相对应. 关键词：     

直拉硅中氮在高温退火过程中对氧沉淀的影响

研究了掺氮直拉硅单晶（NCZ）中氮在高温退火过程中对氧沉淀的影响.通过不同温度高温退 火后，测量氧沉淀的生成量和观察硅片体内微缺陷（BMD）密度与高温形核时间的变化关系 ，同时用透射电子显微镜(TEM)观察氧沉淀及相关缺陷的微观结构.实验结果表明高温退火后 氮对硅中氧沉淀形核有明显的促进作用，在相同退火条件下NCZ硅中BMD密度要远远高于相应 的普通直拉硅.这是由于氮在高温下与氧反应形成氮氧复合体（N-V-O）促进了氧沉淀的形核 ，而且TEM的结果表明氧沉淀的形态都是平板状，周围存在应力场. 关键词： 直拉硅 掺氮 氧沉淀     

硅中热施主的电子结构

利用20—300K的Hall系数测量和6-300K的红外光吸收,研究了含氧P型CZ硅单晶经450℃不同时间热处理后所产生的热施主问题。Hall系数测量表明:经100hr热处理的样品存在两个施主能级:E₁=58meV,E₂=110meV。对不同热处理时间的样品,从低温红外光吸收则可看见由于热施主所引起的复杂吸收光谱。这些吸收峰的数目随着热处理时间的加长而增加和加强。利用类氢模型和有效质量理论拟会和计算,可以证明与氧有关的热施主很可能是双重电荷施主。这些双重施主有多种组态,它与450℃热处理的时间有关。 关键词：     

快中子辐照直拉硅中受主和施主的研究

通过傅里叶红外光谱、正电子湮没寿命谱和Hall技术研究了高剂量快中子辐照直拉硅的辐照 缺陷、电阻率、载流子迁移率、载流子浓度随退火温度的变化.经快中子辐照，直拉硅样品 的导电类型由n型转变为p型.在450和600℃热处理出现两种受主中心，分别由V2_{2O22，V22O，VO22，V-O-V及V44型缺 陷引起，这些缺陷态的出现使得样品中空穴浓度迅速增加；大于650℃热处理这些受主态 缺陷迅速消失， 关键词： 快中子辐照 空位型缺陷 受主 施主}     

氮对金刚石缺陷发光的影响

利用低温显微荧光光谱研究了IIa型、Ib型、Ia型金刚石的缺陷发光性质. 研究发现, 随着氮含量增加, 间隙原子及空位逐渐被氮原子所束缚, 从而使得GR1中心、533.5 nm及580 nm中心等本征缺陷发光减弱, 而氮-空位复合缺陷(NV中心)及523.7 nm中心等氮相关缺陷发光增强. 高温退火后, 间隙原子与空位可以自由移动, IIa型金刚石中出现了NV⁰中心, Ib型金刚石中只剩下了NV中心, Ia型金刚石中氮原子之间发生团聚, 出现了H3中心及N3中心. 另外, 氮作为施主原子, 有利于负电荷缺陷的形成, 如3H 中心、NV^- 中心.     

点缺陷对硼掺杂直拉硅单晶p/p~+外延片中铜沉淀的影响

系统研究了点缺陷对晶体硅中氧沉淀生成的影响,及点缺陷和氧沉淀对重掺硼直拉硅单晶p/p⁺外延片中铜沉淀的影响.样品先在不同的气氛下进行1250℃/60 s快速热处理,随后在750℃/8 h+1050℃/16 h常规热处理过程中引入铜沾污.通过腐蚀结合光学显微镜研究发现,以O₂作为保护气氛时,p⁺衬底中的沉淀密度较小,以Ar和N₂作为保护气氛时,重掺硼p⁺衬底中生成了高密度的沉淀,且在上述所有样品的外延层中均无缺陷生成.研究认为,以O₂作为保护气时引入的自间隙硅原子（Si_I）可以抑制沉淀的形成,而以Ar和N₂作为保护气氛时引入的空位则会促进沉淀的生成,这是导致此差异的主要原因.另外,研究还发现,p/p⁺外延结构能很好地吸除硅片中的铜杂质,从而保持了外延层的洁净.     

低温光致发光研究硅单晶中杂质和缺陷

用低温光致发光技术,研究了硅单晶中浅能级杂质和热处理引进的缺陷,得到各种浓度掺棚和掺磷的硅的光致发光光渚,并作出了相应的定量分析.实验中已探测到的硼的浓度低达5×10~(11)cm~(-3).观察了光致发光强度与激发光强度的关系,还用光致发光技术分析了450℃附近热处理引进的热施主的行为.结果表明,低温光致发光可以作为测量高纯半导体单晶硅中微量杂质硼和磷的含量及分析热处理硅单晶中的缺陷的有效手段.     

在p型硅MOS结构Si/SiO2界面区中与金有关的界面态和深能级

用深能级瞬态谱(DLTS)技术详细研究了金在p型<111>晶向硅MOS结构Si/SiO₂界面区中的行为。结果表明,金与Si/SiO₂界面缺陷H_it(0.494)相互作用形成新的缺陷Au-H_it(0.445),和金在硅的禁带中产生一个能量分布很广的连续界面态,利用这些界面态可以合理地解释金使硅MOS结构平带电压向正方向移动的物理机制。结果还表明,在Si/SiO₂界面附近的半导体中,金施主中心的剖面分 关键词：     

退火直拉硅单晶中氧沉淀和诱生缺陷的电子显微镜研究

本文用超高压透射电子显微镜研究退火的高氧含量无位错直拉硅单晶中氧沉淀和诱生缺陷。在750—1050℃范围内氧沉淀是球状的α方英石。除了球状氧沉淀粒子之外还有一些具有{001}惯习面的方片状氧沉淀物。在950℃以上沿〈110〉方向从氧沉淀发射出冲压式棱柱位错环。这些位错环的柏氏矢量为α/2〈110〉、环面法线为〈110〉,它们是间隙型的位错环。这些位错环是从方片状氧沉淀物或从球伏氧沉淀粒子的聚集团发射出来的。当它们遇到障碍物时可能产生比较复杂的位错组态。实验中观察到由于层错攀移形成的台阶。热处理温度在850℃以下时,未观察到体内层错。 关键词：     

Dirac semimetal in three dimensions

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of β-cristobalite BiO(2) which exhibits three Dirac points at the Fermi level. We find that β-cristobalite BiO(2) is metastable, so it can be physically realized as a 3D analog to graphene.     

New oxygen donors in silicon

Oxygen donor traps and oxygen-related precipitates are investigated by deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). The so-called New Donors (ND's) occur after thermal treatments in the temperature range of 650 °–800 ° C. They have a continuous distribution of trap states with respect to energy in the band gap of Si. The concentration of the trap states increases towards the conduction band edge. The precipitates observed are mainly platelets and ribbon-like defects. The formation and annihilation kinetics of ND traps and oxygen-related precipitates are correlated. An SiO _x Interface Model is proposed to explain the origin and the donor-like behavior of the ND traps. The ND trap spectrum is composed of two different types of trap states: interface states at the surface of precipitates and bound states in the Coulombic wells of a fixed positive charge which is located in the SiO _x precipitates.     

The J.C. Phillips model for vitreous SiO2: A critical appraisal

J.C. Phillips has proposed that the structure of vitreous silica is granular, comprising an agglomeration of 66 Å β-cristobalite paracrystallites the surfaces of which are non-coalescing and saturated with Si=O double bonds. It is shown that this model and several of its variants are incompatible with recent neutron diffraction and Raman spectroscopic data.     

Al-4%Ag合金中Ag原子偏析的低温正电子湮没参数研究

分别研究了823 K淬火处理和20%形变量的Al-4%Ag低温下Ag析出物对正电子的捕获行为的变化。采用正电子湮没寿命谱(PALS)技术和符合多普勒展宽能谱(CDBS)在温度范围10~293 K内对其进行表征。多普勒展宽能谱结果表明2种样品中均存在Ag析出物。正电子寿命谱的解谱结果中的各组分给出了Ag析出物随测量温度的变化规律。在170 ~273 K之间,正电子湮没行为具有较强的温度依赖性。但对于两个具有不同类型缺陷的样品,在低于170 K时观察到样品中Ag析出物捕获正电子能力出现了差异。随着测量温度的降低,淬火样品中的Ag析出物的正电子寿命和强度基本不变。在低于170 K的测量中,形变样品中的Ag析出物对正电子的捕获能力仍旧存在着较强的温度依赖性,但是变化幅度在逐渐减弱。当测量温度提升到室温(273~293 K),越来越多的正电子从Ag析出物中逃逸,逐渐回到自由状态或被其他深陷阱所捕获,失去了对温度的依赖性。     

Atomic-scale computer simulation study of the interaction of Cu-rich precipitates with irradiation-produced defects in α-Fe

Copper-rich precipitates can nucleate and grow in ferritic steels containing small amounts of copper in solution and this affects mechanical properties. Growth kinetics, composition and structure of precipitates under irradiation are different from those under thermal ageing, and also vary with type of radiation. This implies that the interaction between radiation defects, i.e. vacancies, self-interstitial atoms (SIAs) and their clusters, and precipitates is influential. It is studied here by atomic-scale computer simulation. The results are compared with those of elasticity theory based on the size misfit of precipitates and defects, and the modulus difference between bcc iron and bcc copper. It is found that SIA defects are repelled by precipitates at large distance but, like vacancies, attracted at small distance. Copper precipitates in iron can, therefore, be sinks for both vacancy and interstitial defects and hence can act as recombination centres under irradiation conditions. A tentative explanation for the mixed Cu–Fe structure of precipitates observed in experiment and the absence of precipitate growth under neutron irradiation is given. More generally, agreement between the simulations and elasticity theory suggests that the results are not artefacts of the atomic model: both vacancy and interstitial defects in metals may bind to precipitates with weaker cohesion than the matrix.     

Electronic energy structure of SiO2: An application of the recursion method

The electronic structures of α-quartz, β-cristobalite and stishovite have been calculated using semiempirical tight-binding Hamiltonian and the recursion method. The model describes fairly well the valence states and lower conduction bands as well as trends in band gaps and effective charges. For comparison, the electronic structure of α-quartz has been calculated in Harrison's universal first-neighbour parametrization.     

Study of the electrical and optical properties of silicon containing oxygen precipitates

The properties of n-type silicon with oxygen precipitates introduced by three-stage annealing were studied by the electron beam induced current (EBIC) method, deep-level transient spectroscopy (DLTS), and photoluminescence (PL). The presence of extended defects with concentration of ≤10⁹ cm^?3 is revealed by the EBIC method. The concentration of electrically active defects formed in silicon due to oxygen precipitation is estimated from the EBIC contrast and is compared to that obtained from the DLTS data. Comparing the spectra of samples with oxygen precipitates with those of plastically deformed crystals, we can assume that the DLTS and PL spectra of silicon with oxygen precipitates are mainly determined by dislocations.     

X-ray diffraction investigation into the specific features of the growth kinetics of oxygen-containing precipitates in Czochralski-grown silicon crystals

The formation and growth of defects (precipitates and dislocation loops) during isothermal decomposition of a supersaturated oxygen-containing solid solution in Czochralski-grown silicon crystals are investigated using triple-crystal x-ray diffractometry. It is established that oxygen-containing precipitates grow through diffusion and that the formation of dislocation loops is associated with both the coagulation of embedded silicon atoms and the generation of dislocation loops by stresses induced in the vicinity of the oxygen-containing precipitates.     

Size distribution and volume fraction of T1 phase precipitates from TEM images: Direct measurements and related correction

Transmission Electron Microscopy (TEM) can be used to measure the size distribution and volume fraction of fine scale precipitates in metallic systems. However, such measurements suffer from a number of artefacts that need to be accounted for, related to the finite thickness of the TEM foil and to the projected observation in two dimensions of the microstructure. We present a correction procedure to describe the 3D distribution of disc-like particles and apply this method to the plate-like T₁ precipitates in an Al–Li–Cu alloy in two ageing conditions showing different particle morphologies. The precipitates were imaged in a High-Angular Annular Dark Field Microscope (HAADF-STEM). The corrected size distribution is further used to determine the precipitate volume fraction. Atom probe tomography (APT) is finally utilised as an alternative way to measure the precipitate volume fraction and test the validity of the electron microscopy results.