Relaxation processes induced in Si-SiO2 systems by ionizing radiation and pulsed magnetic field treating

Comparison of prolonged relaxation processes induced by ionizing radiation (IR) and pulsed magnetic field treating (PMFT) in p-channel MOSFET elements of integral circuits as well as in the concomitant test MOS-capacitors has been carried out for the first time. Time dependent changes of oxide charge density and interface states energy distribution after the end of X-ray (20 keV, 5 × 10⁴ rad (Si)) were investigated. The unusual result is the appearance of considerable changes of MOS system's characteristics only several days after PMFT with the amplitude 0.3 MA m⁻¹. It was discovered that PMFT caused the considerable unmonotonous changes of shallow donor concentration and generation lifetime in silicon. The PMFT induced the impurity and intrinsic defect reaction in silicon contrary to the defect generation in the oxide and Si---SiO₂ interface by the IR.     

High temperature reaction and defect chemistry at the Si/SiO2 interface

The generation of structural and electrical defects in Si/SiO₂ structures upon high temperature annealing by the oxide decomposition reaction Si+SiO₂→2SiO ↑ has been studied using scanning electron microscopy (SEM) and ramped current-voltage measurements. The SiO decomposition is nucleated at crystalline defects in the substrate and results in the formation of voids in the oxide. The voids grow laterally with annealing time, independent of the nature of the defect. Prior to the formation of physical voids in the oxide, defects become electrically active, leading to low field dielectric breakdown. The breakdown degradation is prevented when the O₂ pressure in the annealing ambient is sufficient to reverse the decomposition reaction by reoxidizing the SiO product at the interface.     

Stress-induced leakage current characteristics of PMOS fabricated by a new multi-deposition multi-annealing technique with full gate last process

In the process of high-k films fabrication, a novel multi deposition multi annealing(MDMA) technique is introduced to replace simple post deposition annealing. The leakage current decreases with the increase of the post deposition annealing(PDA) times. The equivalent oxide thickness(EOT) decreases when the annealing time(s) change from 1 to 2. Furthermore,the characteristics of SILC(stress-induced leakage current) for an ultra-thin SiO_2/HfO_2 gate dielectric stack are studied systematically. The increase of the PDA time(s) from 1 to 2 can decrease the defect and defect generation rate in the HK layer. However, increasing the PDA times to 4 and 7 may introduce too much oxygen, therefore the type of oxygen vacancy changes.     

Radiation response of strained Si---SiO2 layered system

In the presented paper radiation effects in silicon-silicon dioxide systems in the presence of additional tensile and compressive stresses were investigated. These stresses were produced by placing additional layers of SiO₂ or Si₃N₄ on the back side of oxidized silicon wafers.The results obtained indicate that relaxation takes place in the oxide during irradiation and leads to the decrease of the compressive stress in the oxide film. Relaxation of strained bonds causes defect generation and the increase of the oxide charge density. This increase is larger for oxides with higher level of compressive stress. No significant changes of the density of surface states were observed since the additional coatings did not affect the strain gradient in the SiO₂.     

基于辐照前1/f噪声的金属-氧化物-半导体场效应晶体管潜在缺陷退化模型

基于金属-氧化物-半导体-场效应管(MOSFET)辐射损伤的微观机理,推导出了MOSFET经历辐照之后氧化层空穴俘获与阈值电压漂移之间关系的表达式.又根据MOSFET中1/f噪声产生的微观机理,建立了辐照之前MOSFET的1/f噪声功率谱幅值与阈值电压漂移量之间的定量关系,并通过实验予以验证.结果表明,辐照之前的1/f噪声功率谱幅值与辐照之后的阈值电压漂移量存在正比例关系,阈值电压漂移量可以反映出MOSFET内部的潜在缺陷的退化程度,因此,该模型有助于利用1/f噪声参量来表征MOSFET内部潜在缺陷的数量和严重程度.     

Oxide semiconductors for solar to chemical energy conversion: nanotechnology approach

The present work considers the application of oxide semiconductors in the conversion of solar energy into the chemical energy required for water purification (removal of microbial cells and toxic organic compounds from water) and the generation of solar hydrogen fuel by photoelectrochemical water splitting. The first part of this work considers the concept of solar energy conversion by oxide semiconductors and the key performance-related properties, including electronic structure, charge transport, flat band potential and surface properties, which are responsible to the reactivity and photoreactivity of oxides with water. The performance of oxide systems for solar energy conversion is briefly considered in terms of an electronic factor. The progress of research in the formation of systems with high performance is considered in terms of specific aspects of nanotechnology, leading to the formation of systems with high performance. The nanotechnology approach in the development of high-performance photocatalysts is considered in terms of the effect of surface energy associated with the formation of nanostructured system on the formation of surface structures that exhibit outstanding properties. The unresolved problems that should be tackled in better understanding of the effect of nanostructures on properties and performance of oxide semiconductors in solar energy conversion are discussed. This part is summarised by a list of unresolved problems of crucial importance in the formation of systems with enhanced performance. This work also formulates the questions that must be addressed in order to overcome the hurdles in the formation of oxide semiconductors with high performance in water purification and the generation of solar fuel. The research strategy in the development of oxide systems with high performance, including photocatalysts for solar water purification and photoelectrodes for photoelectrochemical water splitting, is considered. The considerations are focused on the systems based on titanium dioxide of different defect disorder as well as its solid solutions and composites.     

Radiative relaxation of low-energy electron excitations and point defects in beryllium oxide

The mechanism by which elementary point defects arise and evolve in beryllium oxide crystals and the latest advances in the dynamics of electron excitations of this compound are considered. Experimental and theoretical results which touch on the generation and evolution of elementary point defects are obtained. The properties of intrinsic and impurity point defects, and the crystal-chemical fundamentals of defect generation, optical and luminescent transitions in them, and color centers are discussed. The electron structure of B²⁺, Al²⁺, Zn⁺, and [Li]⁰ defects, nonisothermal relaxation of paramagnetic centers, thermostimulated recombination processes, and the concept of the coexistence of two types of self-localized excitons in beryllium oxide, radiative annihilation of which gives rise to luminescence in the UV and far UV bands are considered. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 76–93, November, 1996.     

Deep defects generated in n-conducting ZnO:TM thin films

The ferromagnetism in highly transparent and intrinsically n-type conducting zinc oxide doped with 3d transition metals (TM), is predicted to be defect mediated. We investigate the generation of deep defects in n-conducting 1 μm thick ZnO:TM films (TM=Co, Mn, Ti) with a nominal TM content of 0.02, 0.20 and 2.00 at.% grown by pulsed laser deposition on a-plane sapphire substrates using deep level transient spectroscopy. We find that a defect level is generated, independent of the TM content, located 0.31 and 0.27 eV below the conduction band minimum of ZnO:Mn and ZnO:Ti, respectively. Different defect levels are generated in dependence on the Co content in ZnO:Co. This work shows that an optimization of defect-related ferromagnetism in n-conducting ZnO:TM thin films will only be possible if the preparation sensitive formation of deep defects is controlled in the same time.     

铜掺杂氧化锌纳米棒的非线性光学响应竞争特性

利用飞秒脉冲激光激发Cu掺杂ZnO纳米棒,研究其特有的非线性光学性质和激发机制。在激发波长为750 nm的荧光光谱中,二次谐波峰非常弱,几乎可以忽略,存在非常强的激子发光峰和Cu掺杂导致缺陷发光峰。激发强度的增大会导致这两个发光峰强度呈非线性增大,激子发光峰位产生明显红移,而缺陷发光峰位没有变化。进一步增大激发强度,缺陷发光峰强度会出现饱和甚至有所下降,而激子发光峰强度持续增大。当激发波长增加到760 nm时,从样品的荧光光谱可以清楚地识别到二次谐波峰和激子发光峰以及缺陷发光峰并存。随着激发波长的进一步增加,二次谐波强度不断增大,而激子发光峰和缺陷发光峰的强度却随之下降。当激发波长为790 nm和800 nm时,未发现激子发光峰和缺陷发光峰,非线性光谱以二次谐波为主导。研究结果表明,通过选择合适的激发波长和激发强度,可以实现发光颜色的转变,使得Cu掺杂ZnO纳米棒在全光显示方面具有潜在的发展前景。     

Intrinsic defects in GaAs and InGaAs through hybrid functional calculations

Vacancies, antisites, and dangling bonds in GaAs and In_0.5Ga_0.5As are studied through hybrid density functionals. The As antisite is found to have a low formation energy in As-rich conditions and defect levels at mid-gap in correspondence of experimental defect densities at the GaAs/oxide and InGaAs/oxide interfaces. In n-type GaAs, the Ga vacancy also shows defect levels in agreement with measured defect densities and competitive formation energies. For both GaAs and InGaAs, the As dangling bonds are located near the valence band maximum. The Ga dangling bond in GaAs is found just below the conduction band-edge in correspondence of experimentally observed states, whereas its defect level is resonant with the conduction band in InGaAs.     

Modeling the Behavior of a MOS Transistor under Fast Neutron and Gamma Irradiation

A numerical model of trapping of the radiation-induced charge in the bulk and on the surface of the oxide layer of a MOS transistor has been developed. The model takes into account the generation of point defects under fast neutron irradiation. The volume and surface charges obtained by the numerical modeling have been used to calculate the drain—gate characteristic of the MOS transistor exposed to neutron irradiation in different doses and accompanying high-energy gamma-ray irradiation. To model the effect of neutron irradiation, different methods for estimating the rate of point defect generation in a two-component material (SiO2) have been developed. The simulated drain—gate characteristic is shown to agree well with the experimental data obtained at the concentration of hole traps and their capture cross sections lying within the published data for an unirradiated device after exposure to gamma rays from a 60Co gamma source and after irradiation with fast neutrons with an average energy of ∼1 MeV and accompanying gamma rays using a pool-type reactor.     

Generation and removal of pits during chemical mechanical polishing process for MgO single crystal substrate

Magnesium oxide (MgO) single crystal is an important substrate for high temperature superconductor, ferroelectric and photoelectric applications. The function and reliability of these devices are directly affected by the quality of polished MgO surface because any defect on the substrate, such as pit or scratch, may be propagated onto device level. In this paper, chemical mechanical polishing (CMP) experiments were conducted on MgO (1 0 0) substrate using slurry mainly comprised of 1-hydroxy ethylidene-11-diphosphonic acid (HEDP) and silica or ceria particles. Through monitoring the variations of the pits topography on substrate surface, generation and removal mechanism of the pits were investigated. The experimental results indicate that the pits were first generated by an indentation or scratch caused by particles in the slurry. If the rate of chemical etching in the defect area is higher than the material removal rate, the pits will grow. If chemical reaction in the defect area is slower than the material removal rate, the pits will become smaller and eventually disappear. Consequently, these findings may provide insight into strategies for minimizing pits during CMP process.     

On structural defect generation induced by thermal fluctuations in materials with a perfect lattice under dynamic loading

The possibility of structural defect generation induced by thermal fluctuations in single crystals under high-rate deformation is numerically investigated. It is shown that thermal fluctuations can be a reason for structural defect generation and there is a threshold strain value at which zones with local structural changes grow almost abruptly.     

Sonochemical modification of carbon nanotubes for enhanced nanocomposite performance

Multi-walled carbon nanotubes (CNTs) have been treated using 20 kHz ultrasound in combination with dilute nitric and sulfuric acids at much lower concentrations than previously reported. The measurements revealed an optimum set of sonication conditions (in this case 30 min at 12 W cm⁻²) exists to overcome aggregation of the nanotubes and to allow efficient dispersion in ethanol or in chitosan. Transmission electron microscopy and Raman spectroscopy suggested the removal of amorphous material and reduction of the CNT diameter as well as modifications to their defect structures. The surface oxidation was determined by FTIR spectroscopy. At longer times or higher ultrasound intensities, degradation such as nanotube shortening and additional defect generation in the graphitic network occurred and the benefits of using ultrasound decreased. The modified CNTs were used as fillers for chitosan films and gave a tenfold increase in tensile strength and integrity of the films. The methodology was combined with sonochemical generation of gold or iron oxide nanoparticles to produce a range of functional membranes for catalytic reductive hydrogenation or dye degradation under conditions that are more environmentally benign than those previously used. Our results further add to the usefulness of sonochemistry as a valuable tool in preparative materials chemistry but also illustrate the crucial importance of careful control over the experimental conditions if optimum results are to be obtained.     

Bias-dependent generation and quenching of defects in pentacene

We describe a defect generation phenomenon that is new to organic semiconductors. A defect in pentacene single crystals can be created by bias-stress and persists at room temperature for an hour in the dark but only seconds with 420 nm illumination. The defect gives rise to a hole trap at Ev+0.38 eV and causes metastable transport effects at room temperature. Creation and decay rates of the hole trap have a 0.67 eV activation energy with a small (10(8) s(-1)) prefactor, suggesting that atomic motion plays a key role in the generation and quenching process.     

The negative role of the fast electrons in the microwave oxidation of silicon

The influence of the fast electrons (up to approx. 100 eV), created in the magnetoactive oxygen plasma, with respect to the silicon oxide growth and oxide properties has been studied. The low values of the oxide dielectric strength and great density of the oxide defect charges have been found on damaged oxides. An upper energy limit (less than approx. 30 eV) has been introduced for the plasma electrons to prevent the oxide defects and extremal heating of the silicon sample during oxidation process.     

X-ray diffraction imaging investigation of silicon carbide on insulator structures

A new process was recently developed to manufacture silicon carbide on insulator structures (SiCOI). The process consists of several steps: (i) hydrogen implantation into an oxidised SiC wafer, (ii) bonding the oxidised surface of this wafer to an oxidised silicon substrate and (iii) high temperature splitting of a thin SiC film from the SiC wafer at the depth of the maximum hydrogen concentration and further annealing of the splitted film. The defect generation occurring during this process was investigated by synchrotron radiation X-ray diffraction topography, with special emphasis on to the last two steps. Various X-ray topographic techniques were used to characterise the lattice defects inside the SiC wafer, to quantify the strong lattice distortion near the edges of the splitted SiC film and to reveal SiC film regions lost during the splitting process. Moreover, we show that the strain fields of dislocations, observed in the silicon substrate after high temperature splitting and annealing of the splitted structure, induce a corresponding deformation in the thin SiC overlayer, despite the presence of the sandwiched oxide film. The defect density is much lower in the central region of the SiCOI structure. Received: 29 June 2001 / Accepted: 8 November 2001 / Published online: 20 March 2002     

Comparison of vacancy and antisite defects in GaAs and InGaAs through hybrid functionals

The formation energies and charge transition levels of vacancy and antisite defects in GaAs and In(0.5)Ga(0.5)As are calculated through hybrid density functionals. In As-rich conditions, the As antisite is the most stable defect in both GaAs and InGaAs, except for n-type GaAs for which the Ga vacancy is favored. The Ga antisite shows the lowest formation energy in Ga-rich conditions. The As antisite provides a consistent interpretation of the defect densities measured at mid-gap for both GaAs/oxide and InGaAs/oxide interfaces.     

A model for the spatial distribution and transport properties of defects in mixed ionic-electronic conductors part I: Defect concentration — Pressure relationships and the spatial distribution of defects

The spatial distribution and transport of defect species in a mixed ionic-electronic conductor (MIEC) depend on the activity of the external gas phase at either side of the MIEC, the defect equilibria and mobility of the species within the MIEC. Previous researchers [1, 2] developed models for defect distribution and transport based on various assumptions, the most prevalent of which is that the concentration of the ionic defect species is constant through the range of activities of the external gas phase in which the MIEC finds application. However, the defect equilibria for many MIECs do not support this assumption. It is desirable, therefore, to have explicit, analytical expressions for the spatial distribution of the defects as a function of position and the flux as a function of the activity gradient of the defect species and the gas phase. Towards the development of such a model, the defect concentration-oxygen partial pressure dependence in an oxide MIEC, such as Ce_0.8Sm_0.2O_2−δ, is considered. From the defect equilibria, equations are developed for the dependence of the defect species on the oxygen activity in the oxide MIEC. Then, to relate the defect equilibria to the spatial parameters of the MIEC, an analytic expression for the variation of oxygen activity as a function of position in an electrolyte is derived. Equations relating oxygen activity to position and defect concentration to oxygen activity are then combined to obtain a defect concentration-position relation. All the relations are derived without the assumption of constant vacancy concentration. Finally, the results are compared with those of previous models.     

0.25-μm PMOSFETs中热载流子的退化特性和解释

本文研究了深亚微米PMOSFETs的热载流子效应。研究发现热载流子效应包括界面态的产生和氧化层中固定正电荷的形成。通过实验证明了深亚微米PMOSFETs中这两种机制的重要性。首先，氧化层固定正电荷的产生在深亚微米PMOSFETs中起作用，使得器件的阈值电压退化，最终限制了表面沟道晶体管的使用寿命。对于先进的模拟和混合信号的应用，工艺和器件的可靠性必须按照阈值电压的漂移重新定义，而不仅仅依照跨导的退化或者栅氧化层的寿命来定义。其次，空穴注入产生的界面态也影响器件的特性。推断了热载流子效应的形成过程。