Anisotropic dopant diffusion in Si under stress using both continuum and atomistic methods

In this paper we present a predictive simulation capability for dopant diffusion under anisotropic non uniform stress/strain using two different simulation techniques: continuum and atomistic Kinetic Monte Carlo (KMC). Due to the different nature of these techniques, different implementations have been developed. We explain the necessity and show the details of these implementations. The continuum model uses an anisotropic tensor matrix to simulate the diffusion. For the atomistic model, diffusion is the composition of multiple hops with different rates. For each particle, a different migration rate per axis is used. The value of the rate takes into account the local stress tensor. The stress is also utilized for modeling surface point defect injection and dopant pairing. These models have been included in a TCAD simulator (Synopsys: Sentaurus reference Manual, 3rd edn., [2007]) as an extension to the already existing models. We show that both continuum and atomistic approaches predict similar behavior for boron diffusion under tensile and compressive stresses in 2D.     

Models for numerical device simulations of crystalline silicon solar cells��a review

Current issues of numerical modeling of crystalline silicon solar cells are reviewed. Numerical modeling has been applied to Si solar cells since the early days of computer modeling and has recently become widely used in the photovoltaics (PV) industry. Simulations are used to analyze fabricated cells and to predict effects due to device changes. Hence, they may accelerate cell optimization and provide quantitative data e.g. of potentially possible improvements, which may form a base for the decision making on development strategies. However, to achieve sufficiently high prediction capabilities, several models had to be refined specifically to PV demands, such as the intrinsic carrier density, minority carrier mobility, recombination at passivated surfaces, and optical models. Currently, the most unresolved issue is the modeling of the emitter layer on textured surfaces, the hole minority carrier mobility, Auger recombination at low dopant densities and intermediate injection levels, and fine-tuned band parameters as a function of temperature. Also, it is recommended that the widely used software in the PV community, PC1D should be extended to Fermi-Dirac statistics.     

Modeling of junction formation in scaled Si devices

In this article, modeling of junction formation in scaled Si device is shown. An atomistic kinetic Monte Carlo (KMC) diffusion modeling is used for the analysis of dopant diffusion and defects during shallow junction formation processes. Dopant diffusion and defect evolution during sub-millisecond non-melt laser annealing (NLA) are studied in both experiments and an atomistic kMC diffusion modeling. Pre-amorphization implant is often used for ultra shallow junction formation. It is shown that Solid Phase Epitaxial Regrowth (SPER) annealing stage plays an important role for dopant diffusion in junction formation process. As Ge implant energy is increased, damage structure and IV composition of Amorphous Pockets are changed and this affects the dopant diffusion and activation behavior. KMC simulations show that B, As deactivation is induced by the formation of dopant-defect complexes, such as B _n I _m , As _n V _m , As _n I _m , As _n , during millisecond annealing time range. Both experiments and KMC show that defect evolution during millisecond annealing time range. Fluorine, Carbon co-implant effects are also modeled using KMC.     

Emission mechanism in rubrene-doped molecular organiclight-emitting diodes: direct carrier recombination at luminescentcenters

The emission mechanism in molecularly doped organic light-emitting diodes, where the emitting layer is composed of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the host and 5,6,11,12-tetraphenylnaphthacene (rubrene) as the dopant, is investigated in terms of energy transfer and direct carrier recombination. Hole trapping by rubrene is identified by current versus voltage and mobility measurements in single-layered devices. Shallow traps are formed and are found to be filled by injected holes at electric field above 2×10⁵ V/cm. Electroluminescence observed in single-layered devices indicate that electrons can be injected directly into the hole transporter, TPD. In double-layered devices composed of TPD and tris-(8-hydroxyquinolinato) aluminum(III) (Alq₃), the penetration depth of electrons into undoped TPD is determined to be ⩽5 nm from the Alq₃ interface. Upon doping with rubrene, the emission zone is extended to 20 nm due to the increase in the electron penetration depth. This is attributed to the transition of the electron hopping sites from TPD to rubrene molecules. At high-rubrene concentration, electron transport occurs via hopping on the rubrene molecules. The dominant emission mechanism in rubrene-doped TPD is attributed to the electron-hole recombination at the dopant molecule. This is maximized by hole trapping and electron transport of rubrene     

A 1D numerical model for rapid stress analysis in bipolar junction transistors

Stress effects in semiconductor devices have gained significant attention in semiconductor industry in recent years, and numerical modeling is often used as a powerful tool for stress analysis in semiconductor devices. Here, we present a nontraditional 1D model for fast stress analysis in bipolar junction transistors. Because bipolar transistors are operationally 1D devices, it is possible to speed up the simulation with a 1D numerical model and get results that are comparable with 2D and 3D simulation outcomes. This model consists of a complete numerical algorithm that can be used for stress analysis of bipolar transistors on any plane. Existing 1D simulators take more time as they solve all device equations throughout the device. In contrast, our model optimizes the solutions for different regions with the development and inclusion of specific algorithms. A fractional starting point is introduced for the depletion region to speed up the process further. This way, faster computing time and much higher accuracy can be reached. At the same time, popular 2D and 3D simulators, which are using finite element methods, are naturally much slower, especially if high accuracy is needed. Simulation results of this 1D model match well with the simulation results of a 2D model developed with a commercial technology computer aided design (TCAD) tool. The validity of our model was verified with experimental results and theoretical expectations as well. Copyright © 2016 John Wiley & Sons, Ltd.     

Transport in silicon nanowires: role of radial dopant profile

We consider the electronic transport properties of phosphorus (P) doped silicon nanowires (SiNWs). By combining ab initio density functional theory (DFT) calculations with a recursive Green’s function method, we calculate the conductance distribution of up to 200 nm long SiNWs with different distributions of P dopant impurities. We find that the radial distribution of the dopants influences the conductance properties significantly: surface doped wires have longer mean-free paths and smaller sample-to-sample fluctuations in the cross-over from ballistic to diffusive transport. These findings can be quantitatively predicted in terms of the scattering properties of the single dopant atoms, implying that relatively simple calculations are sufficient in practical device modeling.     

Effects of Mg dopant on the degradation of InGaN multiple quantum wells in AlInGaN-based light emitting devices

We investigated the effects of Mg dopant on the degradation of AlInGaN-based light emitting diodes (LEDs) and laser diodes (LDs) with InGaN multi-quantum wells (MQWs). Photoluminescence (PL) intensity of InGaN MQWs was significantly decreased with increasing the Mg intentional doping process in InGaN active region, indicating that Mg dopant could degrade the optical quality of InGaN MQWs. From secondary ion mass spectroscopy (SIMS) analysis of AlInGaN-based LDs grown on GaN/sapphire and GaN substrate with different dislocation densities, we found that Mg concentration of LD on GaN/sapphire was higher than that of LD on GaN substrate at the InGaN MQWs regions. Additionally, we observed that Mg atoms were significantly diffused from p-type layer to InGaN MQWs region in the LD structure after aging evaluation. From these results, we could conclude that Mg diffusion along threading dislocations is one of the major gradual degradation mechanisms of AlInGaN-based LD/LEDs during the device operation under high voltage condition.     

Rare earth doped fluoride waveguides fabricated using molecularbeam epitaxy

We have grown planar waveguides of rare earth doped single crystal fluoride films on insulating and semiconductor substrates using molecular beam epitaxy and have formed channel waveguides by ion milling. Structural and spectral analysis demonstrates that excellent crystallinity is being achieved and that the rare earth ion is incorporated into the film at sites and in charge states similar to bulk laser hosts. Lifetime measurements confirm that the local environment of the dopant ion is essentially that found for bulk materials. Single and higher order optical mode propagation has been demonstrated for the channel waveguides. By exciting individual channels with an 800 nm pump, we have generated strong upconversion fluorescence in Er and Nd doped guides. The ability to fabricate these waveguides On semiconductor substrates substantiates the potential for on chip integration of both IR downconversion lasers and IR pumped upconversion visible and UV lasers with a diode laser pump source. The use of transition metal dopants is possible and would enable tunable operation. Waveguide propagation loss in present devices must be reduced to realize a laser oscillator and we discuss how this is being addressed     

Oxygen Diffusion in Single- and Poly-Crystalline Zinc Oxides

¹⁸O diffusion coefficients were measured in zinc oxide ceramics using a secondary ion mass spectrometer. The results are interpreted as indicating extrinsic behavior. The values of the lattice diffusion coefficients with higher valence dopants compared with zinc ions are greater than lower valence dopant such as lithium ions. Using the data at deeper depth, the grain boundary diffusivity of oxide ions was also evaluated. Although the lattice diffusion coefficients varied by two orders of magnitude, the products of grain boundary width and grain boundary diffusion coefficient were less sensitive to the type of dopants.     

Challenges and opportunities for process modeling in the nanotechnology era

Process modeling is a very diverse area with respect of the processes and materials to be treated as well as concerning the methods to be used. In this paper an outline of the scope of process modeling and simulation is given. Challenges and opportunities are discussed referring especially to the challenges identified in the Modeling and Simulation chapter of the International Technology Roadmap for Semiconductors. Some related results of Fraunhofer IISB are presented. Overall, TCAD including process modeling and simulation is an indispensable tool for the further development of semiconductor technologies and devices, and offers large opportunities to support and partly enable future scaling in More Moore, but also the further improvement of More than Moore devices and systems.     

锂离子电池正极材料LiFePO_4掺杂改性研究进展

橄榄石型LiFePO4是近年发展起来的一种锂离子电池正极材料,但是LiFePO4的电子电导率极低,Li+扩散速度慢,限制了其实用化,其中一种很有效的方法就是在LiFePO4的晶格中掺杂金属离子,使其产生晶格缺陷,促进Li+扩散,改善晶体内部的导电性能。综述了LiFePO4近几年离子在Li(M1)位和Fe(M2)位掺杂的研究进展。     

A Comprehensive TCAD Approach for Assessing Electromigration Reliability of Modern Interconnects

The demanding task of assessing long-time interconnect reliability can only be achieved by combination of experimental and technology computer-aided design (TCAD) methods. The basis for a TCAD tool is a sophisticated physical model which takes into account the microstructural characteristics of copper. In this paper, a general electromigration model is presented with special focus on the influence of grain boundaries and mechanical stress. The possible calibration and usage scenarios of electromigration tools are discussed. The physical soundness of the model is proved by 3-D simulations of typical dual-damascene structures used in accelerated electromigration testing.      

Theoretical Study of Boron Clustering in Silicon

Ion implantation is the method of choice to introduce dopants such as boron into silicon. Thermal anneals are used to heal the implant damage as well as to activate the dopant electrically. The implant-anneal cycle causes transient enhanced diffusion (TED) of boron and clustering of boron atoms at concentrations far below the solubility limit. The formation of these small immobile boron-interstitial clusters (BICs) causes the deactivation of boron. In this work, we use density-functional theory calculations to study the boron clustering process in Si. We determine the minimum-energy structures of these clusters at different sizes embedded in bulk Si and calculate the energy and charge state of each cluster within density-functional theory. Special care is taken with regard to structural minimization, charge state effects and energy corrections. In contrast to previous work, we argue that substitutional-boron clusters as defined previously are meaningless due to the high repulsive energy of nearest-neighbor boron atoms. We compare the larger clusters to the phase of precipitates at higher boron concentrations, Si_1.8B_5.2, and suggest the boron icosahedron as logical final BIC before the formation of more macroscopic precipitates in the absence of kinetic constraints. We also describe in detail the implementation of our ab-initio results into a continuum model, which we have used in previous work to simulate diffusion and deactivation of boron.     

基于漂移扩散模型方程的IGCT电路模型

现有基于双极扩散方程(ADE)的功率半导体器件模型只能准确描述准中性区载流子分布,应用于高压器件建模时精度有限。提出一种基于漂移扩散模型(DDM)的集成门极换流晶闸管(IGCT)电路模型的建模方法以提高模型精度。通过分析发现,求解变量数量级相差较大,以及由高掺杂浓度决定的特征参数是影响模型特性的主要因素。由此,通过边界高掺杂区域的解析建模、简化基区求解的边界条件以及应用移动网格法求解DDM提高了模型的稳定性和计算速度。最后,IGCT双脉冲测试仿真与实验对比结果表明在仿真耗时接近的前提下,该方法相对于现有基于ADE模型可以更好地仿真器件在关断振荡以及穿通时的特性。     

Modeling of defects,dopant diffusion and clustering in silicon

Ion implantation is a very well established technique to introduce dopants in semiconductors. This technique has been traditionally used for junction formation in integrated circuit processing, and recently also in solar cells fabrication. In any case, ion implantation causes damage in the silicon lattice that has adverse effects on the performance of devices and the efficiency of solar cells. Alternatively, damage may also have beneficial applications as some studies suggest that small defects may be optically active. Therefore it is important an accurate characterization of defect structures formed upon irradiation. Furthermore, the technological evolution of electronic devices towards the nanometer scale has driven the need for the formation of ultra-shallow and low-resistive junctions. Ion implantation and thermal anneal models are required to predict dopants placement and electrical activation. In this article, we review the main models involved in process simulation, including ion implantation, evolution of point and extended defects and dopant-defect interactions. We identify different regimes at which each type of defect is more relevant and its inclusion in the models becomes crucial. We illustrate in some examples the use of atomistic modeling techniques to gain insight into the physics involved in the processes as well as the relevance of the accuracy of models.     

掺杂稀土元素对Ni(OH)2晶格的影响

首次研究了掺杂稀土元素La、Nd对Ni(OH) 2 晶格的影响 ,通过掺入异种高价离子 ,改变了Ni(OH ) 2 的晶格常数 ,特别是c轴的增加 ,改善了材料的质子扩散性能 ,减少了电化学反应的阻力。另外 ,掺杂异价离子降低了Ni2 的局域能级 ,引入了大量的正缺陷。相对于未掺杂晶体 ,其OH-的数量增多 ,增大了质子扩散的几率 ,因而提高了材料的电化学性能。     

On the ionic conductivity of strongly acceptor doped, fluorite-type oxygen ion conductors

We present an analytical model for the ionic conductivity of a strongly acceptor doped, fluorite-type oxygen ion conductor, (A_{1 −} x _B B _{x B} )O_{2 − x B/2}, i.e. a concentrated solution of AO₂ and B₂O₃, which can be applied, e.g., to yttria doped zirconia (YSZ). The model considers nearest neighbor interactions between oxygen vacancies and dopant cations, which may be negligible, attractive or repulsive. The vacancies are distributed to the tetrahedra formed by the cations using quasi-chemical reactions for the exchange between the different sites. The resulting vacancy distribution is used in a simplified model for the oxygen ion conductivity which considers jump rates between different oxygen sites that depend on their local neighborhood and the nature of the cation-cation edge which has to be crossed during a jump between edge-sharing tetrahedra. Among the various possibilities, only attractive dopant-vacancy interaction together with reduced jump rates through A-B and B-B edges (compared to A-A edges) can explain satisfactorily the experimental findings, i.e. the maximum of the conductivity at dopant fractions x _B ≈ 0.15, the slight decrease of the activation energy with increasing temperature and the increase of activation energy with dopant fraction.     

Improvement of electrical characteristics of local BOX MOSFETs by heavily doped structures and elucidation of the related mechanism

We proposed heavily doped silicon between insulators (HDSBI) MOSFETs to improve electrical characteristics of local BOX MOSFETs by using simple structures that combine local BOX regions with additional doped regions. HDSBI MOSFETs have heavily doped regions between local BOX regions, in which acceptors or traps are introduced. Simulated electrical characteristics demonstrated that they can suppress the SCEs and the kink effect, as well as the self-heating effect (SHE), which is suppressed by conventional local BOX MOSFETs. We elucidated how the additional doped regions in HDSBI MOSFETs suppress the SCEs and the kink effect. We concluded that HDSBI MOSFETs are suitable for applications, such as multi-purpose system-on-chip on which both short-channel logic circuits and high drive current circuits are integrated.     

锂离子电池正极材料稀土掺杂研究进展

作为一种新型的高效绿色电池,稀土掺杂材料在锂离子电池中得到了广泛的应用,从而成为稀土应用的重要应用领域之一。阐述了锂离子电池技术发展的重要性,综述了稀土掺杂对锂离子电池正极材料结构和电化学性能的影响。重点介绍了稀土掺杂尖品石锰酸锂正极材料研究进展,展望了稀土掺杂在锂离子电池正极材料中的应用发展前景,并认为随着稀土掺杂研究的深入,采用稀土掺杂以进一步推动高性能锂离子电池的发展,是今后高比容量电池发展的一个重要领域。     

Electrochemical capacitance-voltage characterization of plasma-doped ultra-shallow junctions

Ultra-shallow Si p⁺n junctions formed by plasma doping are characterized by electrochemical capacitance-voltage (ECV). By comparing ECV results with those of secondary ion mass spectroscopy (SIMS), it is found that the dopant concentration profiles in heavily-doped p⁺ layer as well as junction depths measured by ECV are in good agreement with those measured by SIMS. However, the ECV measurement of dopant concentration in the underlying lightly doped n-type substrate is significantly influenced by the upper heavily-doped layer. The ECV technique is also easy to control and reproduce. The ECV results of ultra-shallow junctions (USJ) formed by plasma doping followed by different annealing processes show that ECV is capable of reliably characterizing a Si USJ with junction depth as low as 10 nm, and dopant concentration up to 10²¹ cm⁻³. Also, its depth resolution can be as fine as 1 nm. Therefore, it shows great potential in application for characterizing USJ in the sub-65 nm technology node CMOS devices. __________ Translated from Chinese Journal of Semiconductors, 2006, 27(11): 1966–1969 [译自: 半导体学报]