无限深势阱问题的可视化研究

基于计算软件对一些常见的无限深势阱进行了可视化研究,并设计了GUI界面实现对势阱的选择.在选定势阱后,设置好相应的势阱参数和量子数,便可依次绘制出低维势阱的波函数、概率密度函数和三维势阱中的电子云图像.文中分析了二维和三维势阱中能级的简并度问题,并重点讨论了不同势阱波函数和概率密度函数随量子数的变化规律.将势阱问题可视...     

量子阱垒层掺杂变化对双波长LED调控作用研究

采用APSYS软件研究了InGaN/GaN量子阱垒层掺杂变化对双波长 发光二极管发光光谱的调控问题. 在不同掺杂类型和浓度下对器件电子空穴浓度分布、 载流子复合速率、 能带结构、 发光光谱进行分析, 结果表明, 调节量子阱垒层n型和p型的掺杂浓度可以精确而有效地根据需要调控发光光谱, 解决发光光谱调控难的问题. 这些现象归因于掺杂的量子阱垒层对电子空穴分布的调控作用.     

准幻核中的近似广义辛弱数守恒（英文）

对称性在了解诸如原子核的转动、自旋和宇称、及同位旋等核结构性质中都起着重要的作用,并且使复杂的原子核结构问题得以简化。辛弱数就是由于原子核的对相互作用中的对称性所导出的众所周知的好量子数。通过对丰中子和缺中子核素及核素的高自旋态的衰变数据分析来揭示辛弱数的近似守恒性质。研究结果表明,在准幻核的高自旋同质异能素链中,无论所涉及的价空间的核子轨道有何不同,广义辛弱数总是近似的好量子数。Symmetry plays an important role in understanding the nuclear structure properties from the rotation of a nucleus to the spin, parity and isospin of nuclear states. This simplifies the complexity of the nuclear problems in one way or the other. Seniority is also a well known quantum number which arises due to the symmetry in the pairing interaction of nuclei. We present empirical as well as theoretical evidences based on decay rates which support the goodness of seniority at higher spins as well as in nrich or, n-deficient nuclei. We find that the generalized seniority governs the identical trends of high-spin isomers in different semi-magic chains, where different set of nucleon orbitals from different valence spaces are involved.     

On the intersubband interactions in an electron-hole plasma confined in a quntum well

We calculate the shrinkage of the gaps between the different subbands of a quantum well induced by the presence of a photo-excited electron-hole plasma. The reduction of the higher gaps is found to be almost as strong as that of the fundamental gap. We discuss the importance of the interactions between the different subbands. Our theoretical results compare well with optical transmission experiments.     

Application of Free Carrier Absorption for Far-Infrared Detection

Far-infrared (FIR) free-carrier absorption characteristics for epitaxially grown p-type Si and GaAs thin films over a range of carrier concentrations have been investigated, both experimentally and theoretically, and employed to analyze the experimental results of FIR detection. The free-hole absorption is found to be almost independent of the wavelength and a linear regression relationship between the absorption coefficient and the carrier concentration has been obtained, which can be applied to well explain the behavior of GaAs FIR detectors with different number of layers, different applied biases, as well as different layer concentrations.     

不同晶格常数光子晶体构成的光量子阱中的共振模

用基于平面波的传输矩阵法分析由具有不同晶格常数的光子晶体材料构成的光量子阱结构中的共振模，发现湮没于垒层的阱层能带分离成共振模，且共振模的数目随阱层的厚度变化而改变。提出一种新型的非对称量子阱结构模型，由2块晶格常数不同的光子晶体材料和夹在光子晶体材料中间作为阱层的均匀介电材料构成，并对其中的共振模进行了分析。指出当阱层厚度达到构成垒层的光子晶体晶格常数的一半时出现一个共振模，若继续小量增加阱层厚度将使共振模频率出现红移。最后给出一种基于平面波的传输矩阵法，且对于不同晶格常数的光子晶体量子阱结构均有效的数值模拟方法，可用于研究由三维光子晶体材料或者色散材料组成的光子晶体量子阱结构。     

Photonic resonant transmission in the quantum-well structure of photonic crystals

A photonic quantum-well is constructed by sandwiching a uniform medium between two photonic barriers due to the photonic band gap mismatch, similar to electronic quantum well. The transmission coefficient is calculated by a plane-wave expansion method in combination with multiple-scattering techniques. The transmission peaks indicate that some photonic states exist in a quantized way, satisfying a quantized frequency relation. We also show that the finite photonic potential barrier plays different confined roles on the different photonic levels. The positions and number of the resonant peaks can be artificially tuned by varying the well width. By appropriately choosing the parameters of the well and barrier, a high-quality multichannel filtering can be achieved.     

Effect of ion implantation on quantum well infrared photodetectors

Ion implantation is a postgrowth processing technique which, when combined with annealing, can be used to tune the absorption wavelength of quantum well devices. We have implanted and annealed, three different quantum well infrared photodetector structures, and measured the absorption spectra of the samples by Fourier transform spectroscopy. The peak absorption wavelength shift of each structure has been calculated as a function of diffusion length by simulating the diffusion processes. We found different diffusion rates for the structures and attribute this to different numbers of as-grown defects. Our results indicate that agglomeration of single defects into defect clusters limits the ability of ion implantation to tune the wavelength of a structure with a higher number of as-grown defects. Thus, a structure with the lowest number of as-grown defects is most useful for fabricating a multi-color quantum well photodetector by ion implantation, because in this case ion implantation can enhance the diffusion rate considerably leading to large red- shift in peak absorption wavelength.     

Interband absorption and exciton binding energy in an inverse parabolic quantum well under the magnetic field

We have investigated the effects of the magnetic field which is applied perpendicular to the growth direction of the well on the interband absorption and on the binding energy of the excitons in an GaAs/Ga1−xAlxAs inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and the effective band gap of the system can be modified by changing Al concentration at the well center, the strength of the magnetic field and well dimensions. This case directly influences the nature of electronic and optical properties in this structure.     

牙齿龋齿损伤可见-近红外光谱偏振检测研究

针对不同龋齿损伤程度有效表征问题,探究一种光谱偏振无损低耗的检测方法,作为对常规检测方法如化学分析法、表面轮廓测定法、显微放射照相术的有益补充。牙齿龋齿损伤由脱矿溶解牙釉质与牙本质的钙与磷酸盐造成,牙齿组织表面微观结构发生了不同程度的变化,结构的变化导致其对光波散射特性与相位改变呈现不同程度的差异。基于偏振光谱对观测样本表面微观结构敏感的特征,不同龋齿损伤样本其表面微观结构变化与偏振信息强烈关联,提出一种光谱偏振有效表征牙齿龋齿损伤度的方法。分别选取450,550,670和860 nm四个不同观测光谱研究波段,选择六个不同龋坏程度的实验样本,选取偏振度参量描述不同牙齿样本的光谱偏振特性。实验结果表明,同一观测光谱波段随着牙齿龋坏程度的加深其偏振度表征参量呈现增加趋势,同时,对于同一观测样本450 nm光谱波段的偏振特性强于其他波段,呈现观测光谱波段与其偏振特性负相关关系。为进一步定量刻画偏振光谱与牙齿龋坏损伤等级的表征关系,构建光谱偏振特征参量与不同损伤等级牙齿样本的指数关联数学模型,通过数学模型解译其内在耦合关联。为有效验证构建模型的稳健性,对模型仿真预测结果与实测数据进行定量化验证,选取和方差（SSE）、模型确定系数（R-square）、均方根（RMSE）等评价因子对构建的模型进行定量评判。结果表明,四个不同光谱波段的模型确定系数均接近于1,和方差与均方根数值均较小,且450nm观测光谱波段接近于0,定量评价结果验证了构建模型的稳健性与有效性,构建模型可有效解译不同龋齿样本与光谱偏振特征的耦合关联。该研究内容有效扩展了牙齿龋齿检测方式,揭示了光谱偏振可有效表征龋齿损伤,发展了一种无损低耗的新型偏振光谱检测技术手段。     

Read and write processes, and head technology for perpendicular recording

In this paper, we present a review of the write and read processes in perpendicular magnetic recording. We also discuss their impact, based on recording physics aspects, on design considerations for writers and readers. For the write process, we discuss fundamental write-ability limitations as well as possible paths to ultra-high areal density perpendicular recording. The impacts of different medium designs, geometrical scaling, and the breakdown of scaling, both in terms of write-ability and transition curvature, are shown based on different modeling techniques, including analytical formulas, finite element modeling (FEM), and micromagnetic simulations. Basic design rules as well as alternative designs that enable high areal density are briefly explained. For the read-back process, the relation between reader signal to noise ratio (SNR) and resistance, as well as reader resistance shunt and spacing loss, are discussed. Finally, we use a simple example to illustrate, both from a write as well as a read-back perspective, the complicated nature of perpendicular recording systems, and how different medium designs impact recording head technology for ultra high density perpendicular recording.     

Binding energy of impurity states in an inverse parabolic quantum well under magnetic field

 We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x_max=0.3. The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions.     

Self-channelling of electric current in a quantum well

We have directly demonstrated that homogeneous photoexcitation of a quantum well in presence of uniform tilted magnetic field gives rise to a set of bypass in-plane electric currents of a different value which may flow even in the opposite directions simultaneously. The effect has been observed in an asymmetric InAs quantum well under the Landau quantization. Theoretical model of the effect are discussed as well as the related problems.     

Multicolour spatial frequency analysis by optical multiplexing

The Fourier transforms of colour transparencies have been separated spatially according to their colour content. The use of a different spatial carrier for each colour enables simultaneous detection of the spectra as well as reconstitution of an image after different spatial filtering processes have been performed on different colour spectra.     

The influence of interdiffusion on the binding energy of excitons in InxGa1−xNyAs1−y /GaAs quantum wells

The influence of a technologically important effect of interdiffusion of atoms between well and barrier layers on the ground state exciton binding energy has been investigated as a function of the well width, for different quaternary material compositions. The migration of the group III atoms through the quantum well interfaces has been assumed to be dominant. Significant changes of the exciton binding energy depending on the diffusion length have been observed.     

Multiple linear feature detection through top-hat transform by using multi linear structuring elements

A multiple linear feature detection algorithm through top-hat transform using the constructed multiple linear structuring elements is proposed in this paper. The desired linear features are treated as a set. And, the set is divided into different subsets. Multi linear structuring elements corresponding to different subsets are constructed. After that, top-hat transform is performed by using the constructed linear structuring elements, and the results are combined to reconstruct the desired linear features. Then, the extracted linear features are binarized and processed to form the final detected binary linear features. Because of the effective performance of the top-hat transform using the constructed multi linear structuring elements, the linear features of different images from different applications could be well detected. The analysis and experimental results show that, the proposed algorithm could be well used for multiple linear feature detection in different applications.     

Resonant modes in quantum well structure of photonic crystals with different lattice constants

The resonant modes in a quantum well (QW) structure composed of three slabs of two dimensional (2D) photonic crystals with different lattice constants are analyzed with plane-wave-based transfer matrix method (TMM). It is found that the energy band of the well slab submerged into the band gap of barrier slab is discretized into quantized modes and the number of the resonant modes changes with the well slab thickness. A model structure of asymmetrical photonic QW consisting of two slabs of 2D photonic crystals with different lattice constants and one uniform dielectric slab in between is proposed and the resonant modes in it are investigated with the same method. A useful numerical simulation method for theoretical discussion as well as for practical application about photonic QW structure of photonic crystals with different lattice constants is proposed.     

The conductance of the NC3 nanodevices: different partial substitution of carbon by nitrogen in graphite

The conductance properties of the two type NC3 nanodevices are investigated by ab initio method. The different substitution of carbon by nitrogen in graphite leads to different band gap energies. Consequently, the conductance of the two type devices appears a large discrepancy and diverse characteristics and each has its own merit. The connecting manner of the NC3 ribbon with electrodes results in different conductance as well. In general, the transport charge capacity alone the NC3 zigzag direction is well than another direction, especially for type 1. The optimization demonstrate type 1 is stable than type 2.     

WELL-WIDTH DEPENDENCE OF THE EXCITON LIFETIME IN GaAs/AlGaAs QUANTUM WELLS

The dependence of the excitonic lifetime on the well width has been studied in conventional GaAs/AlGaAs quantum wells. Two clearly different variations of the measured excitonic lifetime have been observed. For wide well widths, we find a nearly linear decrease of the lifetime with decreasing well width. However, when the well is further decreased, a saturation and even increase of the lifetime with decreeing well width are observed. The experimental data are compared with the theory of radiative excitonic recombination, and show that well width dependence of the measured photoluminescence lifetime can be attributed mainly to the change of the excitonic effective volume and the overlap integral as well.