Applications of Huang–Rhys theory in semiconductor optical spectroscopy

A brief review of Huang–Rhys theory and Albrechtos theory is provided,and their connection and applications are discussed.The former is a first order perturbative theory on optical transitions intended for applications such as absorption and emission involving localized defect or impurity centers,emphasizing lattice relaxation or mixing of vibrational states due to electron–phonon coupling.The coupling strength is described by the Huang–Rhys factor.The latter theory is a second order perturbative theory on optical transitions intended for Raman scattering,and can in-principle include electron–phonon coupling in both electronic states and vibrational states.These two theories can potentially be connected through the common effect of lattice relaxation – non-orthonormal vibrational states associated with different electronic states.Because of this perceived connection,the latter theory is often used to explain resonant Raman scattering of LO phonons in bulk semiconductors and further used to describe the size dependence of electron–phonon coupling or Huang–Rhys factor in semiconductor nanostructures.Specifically,the A term in Albrechtos theory is often invoked to describe the multi-LO-phonon resonant Raman peaks in both bulk and nanostructured semiconductors in the literature,due to the misconception that a free-exciton could have a strong lattice relaxation.Without lattice relaxation,the A term will give rise to Rayleigh or elastic scattering.Lattice relaxation is only significant for highly localized defect or impurity states,and should be practically zero for either single particle states or free exciton states in a bulk semiconductor or for confined states in a semiconductor nanostructure that is not extremely small.     

战斗机红外点源目标特性计算方法

研究了作为点源目标的战斗机红外辐射特性。将飞机的红外辐射分为排气系统辐射和蒙皮辐射两部分,根据红外辐射相关理论,提出了各自的红外辐射计算方法。在排气系统辐射的计算中,将实测数据、流场计算结果与经验公式相结合,并考虑了尾焰对尾喷口辐射的吸收以及多条尾焰的相互作用。通过计算不同状态、不同波段的战斗机红外辐射,得到了目标辐射随方向、速度、高度、发动机状态的变化规律,并验证了所建计算模型的正确性。     

Theoretical comparative studies of charge mobilities for molecular materials: Pet versus bnpery

Charge mobility is the most important issue for organic semiconductors. We calculate the electron and hole mobilities for prototypical polycyclic hydrocarbon molecules, perylothiophene (pet) and benzo(g,h,i)-perylene (bnpery) using Marcus electron transfer theory coupled with a diabatic model and a homogeneous diffusion assumption to obtain the charge mobility. The first-principles DFT calculations show that the hole mobility is about an order of magnitude higher than the electron mobility in pet. However, we find that for bnpery, the electron and hole transports are balanced, namely, very close in mobility, indicating the possible application in light-emitting field-effect transistor. The crystal packing effects on the frontier orbital coupling are found to be essential to understand such differences in transport behaviors.     

High-field electronic conduction in insulators

The quantum theory of electronic transport phenomena in large electric fields in highly dissipative media is critically examined. Serious conceptual problems and computational difficulties arise because neither the field nor the dissipation can be treated as a perturbation. We review a decade-old calculation of the velocity acquired by an electron in a finite electric field in a polar crystal and subsequent work which expanded our understanding of our method and results. A key feature of the earlier work was that in a single curve of electric field vs velocity, all the expected phenomena appeared, including a threshold field for producing hot electrons, in quantitative agreement with experiment, and a decreasing rate of energy loss with velocity for very fast electrons. A more recently studied problem, that of electron acceleration below the threshold field will be discussed. This problem is very important since such acceleration is the necessary precursor of ionization and breakdown. The physical significance of dissipation processes far from thermal equilibrium will also be mentioned.     

Algorithms for sliding block codes---An application of symbolic dynamics to information theory

Ideas which have origins in Shannon's work in information theory have arisen independently in a mathematical discipline called symbolic dynamics. These ideas have been refined and developed in recent years to a point where they yield general algorithms for constructing practical coding schemes with engineering applications. In this work we prove an extension of a coding theorem of Marcus and trace a line of mathematics from abstract topological dynamics to concrete logic network diagrams.     

Numerical Analysis of Radiative Recombination in Narrow-Gap Semiconductors Using the Green’s Function Formalism

A numerical model based on the Green’s function formalism has been developed and used to investigate the radiative recombination processes in multiple narrow-gap semiconductor materials. Full band structures and adaptive band-dependent tetrahedral meshes were adopted to improve the accuracy of the calculation. As a validation, the spectrum of the absorption coefficient for germanium was examined, giving good agreement with the experimental data. The absorption coefficient and radiative recombination lifetime for HgCdTe were then investigated for different compositions, carrier concentrations, and operating temperatures. The results confirmed the accuracy of the widely used theoretical formula for the radiative recombination lifetime under the condition that the effective mass of holes in the formula must be carefully chosen. Based on all our comparisons and calculations, the Green’s function model is proved to be a reliable tool for predicting the radiative recombination properties of HgCdTe, which could further facilitate the investigation of more complicated processes such as photon-recycling issues.     

ON ENERGY CONSERVATION IN RADIATION PROCESS OF ELECTRON BEAM WITHIN A WAVEGUIDE SYSTEM

The formula for the electromagnetic field induced by electron beam in a waveguide witharbitrary cross-section has been derived by using the operator theory of electromagnetic field.In this formulathe normalized eigen function in ordinary dyadic Green's function is replaced by the field induced by unitpower flow.By this formula,the relationship of energy conservation in the radiation process can be proyedeasily and it can be used in the interaction theory for different microwave electron tubes.     

Relating stacking structures and charge transport in crystal polymorphs of the pyrrole-based π-conjugated molecule

We present a theoretical study on charge transport in crystal polymorphs of the pyrrole-based π-conjugated molecule, the dipyrrolyldiketone difluoroboron complex. The ab initio all-electron fragment molecular orbital calculations were carried out to evaluate electronic couplings for charge transfer in three crystal polymorphs. The electron and hole carrier mobilities were estimated on the basis of the master equation combined with the Marcus theory. We found that utilizing the polar diketone difluoroboron unit as the π-conjugated molecule results in the large molecular interactions and electronic couplings. We demonstrate the impact of crystal packing structures on the anisotropy of charge transport, highlighting the dimensionality of charge-transfer networks varying from zero-dimensional behavior of charge localization to three-dimensional behavior of isotropic charge transport. We further elucidate the effects of different π-π stacking modes on the electronic couplings and intermolecular interactions, which underlie the relationship between the crystal packing structures and charge transport.     

Estimation of charge carrier mobility in amorphous organic materials using percolation corrected random-walk model

A computationally simple yet predictive multi-scale simulation scheme is introduced to estimate zero-field charge mobilities for amorphous OSC materials. A percolating charge model is utilized to describe inhomogeneity of hopping trajectories of carriers in amorphous media. The prediction scheme is composed of the following stages: quantum chemical calculation of Marcus inner sphere reorganization energies, molecular dynamics simulations of the amorphous condensed phase bulk structure, automated quantum chemical calculations of the electronic coupling for dimer pairs in the amorphous solid, and calculation of the Marcus theory charge hopping rates and an estimated bulk mobility using the Einstein relation, corrected for the inhomogeneous hopping network of the solid. Comparisons with independent experimental measurements of hole mobility for ten OSC compounds show that this approach gives good correlation between predictions and measurements suitable for ranking systems, and useful quantitative agreement. This low-cost model with minimal complexity is well-suited for incorporation into a virtual materials discovery framework for advanced OSC solutions.     

多色GSM光束通过杨氏双缝后谱强度的一般式

为了统一地研究多色高斯-谢尔模型(GSM)光束通过杨氏双缝衍射后在近场和远场的光谱移动和光谱开关现象,利用部分相干光的广义衍射积分公式,得到了多色GSM光束通过杨氏双缝和ABCD光学系统后的谱强度解析表达式。从该式可看出,多色GSM光束轴上光谱移动的成因是不同频率成分的光具有不同的菲涅耳数。利用谱强度解析式并以自由空间作为ABCD光学系统的典型代表,对多色GSM光束在近场轴上和远场轴外的光谱移动和光谱开关现象作了数值计算研究。结果表明,所得谱强度解析表达式对GSM光束通过杨氏双缝衍射后的光谱移动和光谱开关现象的研究有一定的理论价值。     

A study on photo-induced intramolecular electron-transfer in fullerene-benzothiadiazole-triphenylamine using time-dependent density functional theory

We employed first-principle calculations to study the photo-induced electron transfer (PIET) process of a fullerene-benzothiadiazole-triphenylamine (C60-BTD-TPA), fullerene-diphenylbenzothiadiazole-triphenylamine (C60-PBTD-TPA), and fullerene-triphenylamine (C60-TPA). The ground state geometries of C60-BTD-TPA, C60-PBTD-TPA, and C60-TPA were optimized using density functional theory (DFT). Their excited states were investigated using time-dependent HF, and time-dependent DFT (TDDFT) methods. The long-range corrected CAM-B3LYP functional was found to give the best agreements with the experimentally observed transition energies. CAM-B3LYP-based wave functions were also employed to calculate the charge transfer integrals using generalized Mulliken–Hush (GMH) approach, and the photo-induced charge separation (k_CS) and charge recombination rate constants (k_CR) were calculated using Marcus theory. The results showed the calculated k_CS and observed k_CS of C60-PBTD-TPA and C60-TPA correspond to each other, however, the both of C60-BTD-TPA differ by two orders of magnitude. For k_CR of these compounds, the calculated and observed values were more contrary to each other due to improper application of Marcus electron-transfer theory.     

On the electron flow movement in the decelerated wave field with exponentially positive-going amplitude

Initially homogeneous electron beam movement in longitudinal electric field of the decelerated electromagnetic wave is discussed. The wave amplitude exponentially increases along the electron’s trajectory. Comparison of solutions obtained numerically and analytically by disturbance method for small amplitude as a sixth approximation is made. It is shown that the approximate solution’s error is small when transit angle is small and the error starts catastrophically rising at some angle’s value. The problem is urgent for building the non-linear clinotron’s theory.     

Modeling hole and electron mobilities in pentacene ab-plane

The master equation coupled with the Marcus–Hush electron transfer theory is applied to solve the charge-carrier mobility in pentacene ab-plane. The two-dimension mobilities of hole and electron-carriers are calculated by numerical method. The calculated intrinsic mobilities for hole and electron-carriers are same order of magnitude. The field induced anisotropic hole-carrier mobilities basically agree with Lee et al. experimental results [J.Y. Lee, S. Roth, Y.W. Park, Appl. Phys. Lett. 88 (2006) 252106]. The direction of the highest hole-carrier mobility is clearly assigned. The influences of electric field and carrier density on the mobility are also investigated.     

The Real-Time Detection and Prediction Method for Ballistic Aircraft Based on Distributed Sensor Networks

Space-based detection satellite and remote detection phased array radar are important parts of space security detection system. The aircraft’s detection, tracking and parameter estimation, trajectory prediction with detection satellite and radar are primary problems to be solved in the early detection of ballistic aircraft. This paper mainly studies the simulation of aircraft’s trajectory in early detection phase, the establishment of a dynamic model of the active segment and trajectory simulation and the simulation to generate a multi-level trajectory vehicle’s trajectory data based on the estimation of the key parameters of the aircraft in the single star observing conditions, the trajectory forecast and radar observation conditions for aircraft tracking. Due to the incompleteness of measurements for the single-satellite detection and the bad convergence, this paper proposes a fired at the focal plane method based on the priori template, establish a complete formula derivation algorithm processes, establish a priori standard ballistic template with the simulation trajectory data and the validity of the method using Monte Carlo simulation. Based on the MATLAB graphical user interface, it builds a simulation platform of ballistics aircraft detection probe which can effectively complete the early detection of scene simulation and demonstration. The simulation results show that the method can solve the bad convergence problems of the detection of a single star and it suits for the application to the ballistic vehicle’s key point estimation.     

AlGaN/GaN HEMT栅阶跃脉冲响应实验研究

通过对AlGaN/GaN HEMT漏极电流栅阶跃脉冲响应实验测试,发现栅脉冲相同时,HEMT开启时间在线性区随VDS增加而增加,而在饱和区随VDS增加而减小;在VDS一定时,器件开启时间随栅脉冲低电平的降低而增加。基于表面态电子释放过程与ID、VDS和阶跃脉冲之间关系的分析,提出了用快电子与慢电子释放两种过程来解释表面态电子弛豫,并建立漏极电流响应过程拟合算式。拟合得到与快、慢电子释放相关的时间常数分别为τ1=0.23s、τ2=1.38s,且拟合曲线与实验结果的最大误差不超过测试值的3%。该研究结果有助于电流崩塌机理的进一步探索。     

Size Dependence of the Melting Point of Silicon Nanoparticles: Molecular Dynamics and Thermodynamic Simulation

Semiconductors - The size dependence of the melting point of Si nanoparticles is investigated using molecular dynamics and thermodynamic simulation based on the Thomson’s formula. The...     

Influence of oligothiophene-functionalized co-sensitizer on the electron injection efficiency for multiple dye-TiO2 interface

Co-sensitizer has been employed in dye-sensitized solar cells (DSSCs) to enhance light harvesting at organic/inorganic heterogeneous. Here, the multiple dyes@TiO₂ interface has been investigated by density functional theory simulations, to explore the role of varied oligothiophene-functionalized co-sensitizers on the electron injection efficiency. In presence of co-sensitizers, the simulated absorption spectra broaden with the increasing of the number of thiophene from 0, 1, to 2. Meanwhile, the co-sensitizer modifies the energy alignment of interface, and influences the electronic coupling between dye and TiO₂. Critically, the ratio of electron-hole recombination and electron injection rates k_rec/k_inj based on Marcus theory for both dye and co-sensitizer decrease significantly with increasing of the number of oligothiophene, resulting in the improved electron injection efficiency. Our result implies that the electron injection efficiency depends on the number of thiophene in co-sensitizer largely, and appropriate number plays an active role in tuning the electronic properties of hybrid heterostructure.     

Tartaglia-Pascal’s triangle: a historical perspective with applications

The aim of this paper is to provide a historical perspective of Tartaglia-Pascal’s triangle with its relations to physics, finance, and statistical signal processing. We start by introducing Tartaglia’s triangle and its numerous properties. We then consider its relationship with a number of topics: the Newton binomial, probability theory (in particular with the Gaussian probability density function, pdf), the Fibonacci sequence, the heat equation, the Schrödinger equation, the Black–Scholes equation of mathematical finance and stochastic filtering theory. Thus, the main contribution of this paper is to present a systematic review of the triangle properties, its connection to statistical theory, and its numerous applications. The paper has mostly a scientific-educational character and is addressed to a wide circle of readers. Sections 7 and 8 are more technical; thus, they may be of interest to more expert readers.     

四阶累积量的递推估计及其应用

本文推导一种复数或实数零均值平稳随机过程的高阶累积量估计的递推算法,随机信号的“峰度”递推估计公式,在递推估计公式中引入了随时间变化的“修正”项,使得该递推算法还可适合非平稳过程高阶累积量的估计计算。并且,本文大量计算了多类型。多航速、多舰船辐射噪声的“峰度”值,分析了舰船辐射噪声特性。     

一种新的低复杂度空间调制信号检测算法

空间调制技术(SM)作为一种新颖的多天线传输方案,近年来受到业界的广泛注意。它将输入信息比特分为两部分,一部分用于激活天线,另一部分用于信号调制,来共同承载发送信息。由于SM系统的最大似然(ML)最优检测算法需要穷举搜索激活天线序号和发送的数字调制符号的所有可能情况,它的检测复杂度很高。为此,人们相继提出了一些简化算法。与这些算法思路不同,本文从传统ML最优表达式出发,引入极坐标得到关于星座点幅度和相角的ML等价表达式,同时根据星座点相角的分布特性对相角进行近似,得到了一种新的次最优检测算法。新算法的检测性能比其他次优算法更接近ML,而且计算复杂度低。最后本文通过计算机仿真,验证了新算法的有效性。