Experimental verification of the nature of the high energy tail inthe electron energy distribution in n-channel MOSFETs

Sensitive quantum-yield measurements (M) on n-channel MOSFETs for drain voltages (V_D) near the bandgap voltage of silicon, showed an abnormal bell-shaped M versus gate voltage (V_G) characteristic at 77 K. At higher V_D, M decreases monotonously with increasing V_G. Measured data is interpreted based on the general nature of electron energy distribution published by Monte-Carlo simulation groups and provide simultaneous experimental verification for the presence of a tail that depends strongly on lattice temperature and electron-electron interaction (EEI) broadening of the tail. Our data suggest EEI broadening of the tail even in the subthreshold regime     

时域展宽特性对相关检测性能的影响分析

时域展宽是激光回波脉冲的重要特性,也是影响激光雷达相关检测性能的重要因素。建立了考虑时域展宽特性的激光回波脉冲数学模型,以此模型和相关检测原理为基础分析了时域展宽特性对相关检测测距误差、信噪比的影响,从激光发射脉冲的近高斯能量时间分布模型出发,推导了时域展宽系数的计算公式,并对理论分析和计算结果进行了仿真论证。仿真结果表明:回波脉冲时域展宽系数与其衰减系数成反比,与发射脉冲上升时间成正比,随着时域展宽系数的增大,激光雷达相关检测系统测距误差增大,信噪比降低。     

Effects of electric field on the exciton linewidth broadening dueto scattering by free carriers in semiconducting quantum-well structures

The effects of an applied electric field perpendicular to the well layers on the broadening of the exciton linewidth due to scattering by free carriers in semiconducting quantum well (QW) structures is theoretically investigated based on a finite confining potential model. The dependence of the free carrier-exciton linewidth broadening on carrier concentration, temperature, and well width are calculated and discussed for various electric field strengths. It is found that the influence of the electric field on the linewidth broadening is appreciable in wide wells, while in narrow wells little change is shown even in the presence of a strong electric field     

一种基于随机散射簇的非平稳3D空间信道模型

针对大规模MIMO信道的近场效应和非平稳特性,该文提出适用大规模MIMO信道的一种基于随机散射簇的非平稳3D空间信道模型。采用抛物波前代替球面波前建模近场效应,并分析抛物波前条件下该模型的信道容量。对于大规模MIMO信道的非平稳特性,提出基于散射簇的有效概率确定收发天线阵元的有效散射簇集合,从而建模散射簇沿天线阵列轴的随机演变来合理描述散射簇的出现和消失。仿真结果表明,用抛物波前和有效散射簇的随机演变来建模大规模MIMO信道特征是很好的候选方法。     

光泵亚毫米波激光的理论模型及计算方法( Ⅲ)——在计算中应注意的几个问题

在光泵亚毫米波激光的理论模型及计算方法( Ⅰ) 和( Ⅱ) 的基础上,提出了在计算中应注意的几个问题。如考虑选用迭代法、谐振腔的反馈特性和谐振特性、多普勒展宽效应、压力展宽效应等。     

光泵亚毫米波激光的理论模型及计算方法( Ⅲ)——在计算中应注意的几个问题

在光泵亚毫米波激光的理论模型及计算方法(I)和(Ⅱ)的基础上,提出了在计算中应注意的几个问题。如考虑选用迭代法、谐振腔的反馈特性和谐振特性、多普勒展宽效应、压力展宽效应等。     

Asymmetric quantum well broadband thyristor laser

A broadband thyristor laser based on InGaAs/GaAs asymmetric quantum well (AQW) is fabricated by metal organic chemical vapor deposition (MOCVD). The 3-μm-wide Fabry-Perot (FP) ridge-waveguide laser shows an S-shape I-V characteristic and exhibits a flat-topped broadband optical spectrum coverage of ~27 nm (Δ_-10 dB) at a center wavelength of~1090 nm with a total output power of 137 mW under pulsed operation. The AQW structure was carefully designed to establish multiple energy states within, in order to broaden the gain spectrum. An obvious blue shift emission, which is not generally acquired in QW laser diodes, is observed in the broadening process of the optical spectrum as the injection current increases. This blue shift spectrum broadening is considered to result from the prominent band-filling effect enhanced by the multiple energy states of the AQW structure, as well as the optical feedback effect contributed by the thyristor laser structure.     

Single electron transistor: Energy-level broadening effect and thermionic contribution

In this paper, a theoretical study of single electron transistor (SET) based on silicon quantum dot (Si–QD) has been studied. We have used a novel approach based on the orthodox theory. We studied the energy–level broadening effect on the performance of the SET, where the tunnel resistance depends on the discrete energy. We have investigated the I–V curves, taking into account the effects of the energy-level broadening, temperature and bias voltage. The presence of Coulomb blockade phenomena and its role to obtain the negative differential resistance (NDR) have been also outlined.     

一种雷达信号特征参数评估的新方法

针对传统雷达信号特征参数评估中指标构建不完备、应用背景不强等问题,在研究分类器核函数对特征参数影响的基础上,提出了一种新的信号特征参数评估方法。该方法首先构建了以可分离性、稳定性、复杂性为评估指标的评估体系,给出了特征类内聚集度与类间聚集度的新的度量准则,并基于用户需求对各评估指标权重作层次分析,最后利用指标权重矩阵和指标评分矩阵以打分方式对特征参数的性能进行综合评估并排序。应用结果表明,该评估方法可行有效,能够较好地实现信号特征参数性能的分析和评估,为特征参数的研究与选择提供了依据。     

Splitting and shift of hot magnetophonon resonance peaks in a two-dimensional electron gas

The splitting of the magnetophonon resonance peaks in a two-dimensional electron system is investigated as function of the electric field (or average electron velocity) for different values of the broadening of the Landau levels. We found that for small broadening the maxima in the magnetophonon oscillations are split into two peaks. A new physical interpretation is presented for this splitting which is based on the separate contributions of LO-phonon absorption and emission processes. A shift of the resonance maxima is found when the broadening of the Landau levels is large. A new explanation is given for the apparent temperature and electron density dependence of the optical phonon frequency in heterostructures as determined from magnetophonon resonance experiments. A mechanism is proposed which is able to produce the observed shift in the resonant position and which is consistent with an interaction with the optical phonon mode of the bulk material.     

Intrinsic manifestation of regular pulsations in time-averaged spectra of semiconductor lasers

Time-averaged spectra of pulsating semiconductor lasers are simulated by integrating the numerical solution of multi-mode rate equations. The results obtained show that the linewidth broadening of each longitudinal mode due to the dynamic wavelength shift is accompanied by a characteristic `mode-splitting? effect arising from the integration.     

Bound and quasibound state calculations for biased/unbiasedsemiconductor quantum heterostructures

A complex transcendental equation valid for a wide range of electron energies for semiconductor quantum heterostructures under unbiased or biased conditions is derived. Its complex roots have as real parts the structure eigenenergy levels, and their imaginary parts are directly related to the lifetime of the corresponding eigenenergies. A numerical method is presented that is capable of extracting all these complex eigenenergies. The method is based on the argument principle theorem from complex number theory. Therefore, all the energy levels and lifetimes of bound and quasibound states can be determined. Energy levels and lifetimes can also be calculated in the presence of scattering events when these are modeled with an energy broadening imaginary potential. Extensive comparisons between this numerical method and other currently used techniques are included, proving the generality and the accuracy of this new method     

Comparative Study on Beam Broadening in Optically Controlled and Conventional Phased Array

The bandwidth characteristic of phased array antenna can be represented by the extent of beam broadening as signal bandwidth is increased. By using two kinds of bandpass signals, the beam 3dB-width values for a variety of instantaneous bandwidths in conventional phased array and wide band optically phased array are respectively analyzed and simulated based on both of their models. And some corresponding curves are given.     

Revision on the calculation of optically pumped FIR laser spectrum with Doppler broadening and pressure broadening effects

By means of iteration method and also taking into account Doppler broadening and pressure braodening effect of IR pumping laser, the output power density of optically pumped NH₃ molecules FIR laser is calculated by solving density matrix equations of three-level system. The results of theoretical calculation shows that, in comparison with the FIR laser under the assumption of ideal monochromatic IR pumping, the output power density of FIR laser in the case of Doppler broadening and pressure broadening IR pumping decreases much more. Meanwhile, via the revision of Doppler broadening and pressure broadening effect, the theoretical value of optimum operating gas pressure reduces, which is in better agreement with the experimental value. Further study shows that the revision of Doppler broadening effect is more fit for the conventional FIR laser with a 2m sample tuble and the revision of pressure broadening effect is much more suitable for the miniature FIR laser with a short sample tube of 5 to 20cm in length.     

Photoluminescence and raman scattering characterization of silicon-doped In0.52Al0.48As grown on InP (100) substrates by molecular beam epitaxy

Growth of In_0.52Al_0.48As epilayers on InP (100) substrates by molecular beam epitaxy at different silicon doping levels is carried out. The doped samples show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. There is a reduction in both the AlAs-like and InAs-like longitudinal-optic (LO) phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased. The PL intensity also showed in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.     

Evolution behavior of chirped tan-hyperbolic pulse through single mode fiber in the simultaneous presence of fiber loss,dispersion and self-phase modulation

We present the results of tan-h pulse propagation through single mode fiber in dispersion dominant regime as well as in the simultaneous presence of fiber loss, group velocity dispersion and self-phase modulation. Both un-chirped/chirped cases have been considered. The pulse was propagated using split-step Fourier method based nonlinear Schrödinger equation. Results clearly show that in the absence of fiber nonlinearity, the pulse goes on broadening with the propagated distance. However, in the presence of the fiber nonlinearity, the pulse initially experiences compression and then undergoes broadening at a faster rate. As the value of sharpness parameter increases, the compression also increases. The results of compensation of group velocity dispersion using dispersion compensating fiber considering the setups of pre-, post- and the combination of pre- and post-compensations are also presented. These investigations provide a detailed study and deeper insight about how fiber responses to such type of optical pulses.     

Steady-state electron transport in the III–V nitride semiconductors: A sensitivity analysis

We studied the sensitivity of the steady-state electron transport in GaN to variations in the important material parameters related to the band structure. We found (a) that an increase in the lowest conduction-band-valley effective mass leads to a lowering and broadening of the peak in the velocity-field characteristic, as well as to an increase in the field at which the peak occurs; (b) that increases in the upper conduction-band-valley effective masses dramatically decrease the saturation drift velocity, with very little other effect; (c) that increased nonparabolicity of the lowest conduction-band valley leads to a broadening and shifting to higher electric fields of the peak in the velocity-field characteristic; (d) that increases in the intervalley energy separation lead to moderate increases in the peak drift velocity; and (e) that increases in the degeneracy of the upper conduction-band valleys leads to a moderate decrease in the saturation drift velocity.     

啁啾脉冲激光放大的理论与数值模拟分析

为了比较啁啾脉冲在均匀加宽与非均匀加宽介质中传输的特性,采用分步傅里叶方法进行了理论分析和实验验证,得到了增益窄化、增益饱和、自相位调制效应对脉冲在两种不同介质中频域、时域的演化特征曲线。结果表明,在非均匀加宽介质中,增益窄化效应更加明显,而且增益饱和效应得到了很好抑制,两种加宽介质中脉冲的频谱都起到了拓宽作用,非均匀加宽介质中的频谱比较对称,而均匀加宽介质中的频谱出现了畸变。这一结果对研究啁啾脉冲在综合加宽介质中传输特性是有帮助的。     

A new approach for the morphological segmentation ofhigh-resolution satellite imagery

A new segmentation method based on the morphological characteristic of connected components in images is proposed. Theoretical definitions of morphological leveling and morphological spectrum are used in the formal definition of a morphological characteristic. In multiscale segmentation, this characteristic is formalized through the derivative of the morphological profile. Multiscale segmentation is particularly well suited for complex image scenes such as aerial or fine resolution satellite images, where very thin, enveloped and/or nested regions must be retained. The proposed method performs well in the presence of both low radiometric contrast and relatively low spatial resolution. Those factors may produce a textural effect, a border effect, and ambiguity in the object/background distinction. Segmentation examples for satellite images are given     

啁啾高斯脉冲在光纤中传输的脉冲展宽研究

通过求解非线性薛定谔方程,研究了线性光纤中色散导致的具有初始频率啁啾的高斯脉冲展宽的详细物理过程。得到高斯脉冲在光纤中色散所致的脉冲展宽的特性,啁啾因子对脉冲展宽的影响,并讨论了光纤色散对不同宽度脉）中的影响,对色散补偿等技术的研究具有一定的参考价值。