Negative dielectric relaxation of hot electrons in CdTe

A direct measurement of negative dielectric relaxation in CdTe at room temperature is presented at electric fields where electrons exhibit negative differential mobility. Data have been obtained with the time-of-flight technique, which is suitable to investigate electron diffusion process and space charge effects by means of an analysis of the time and space evolution of an electron charge layer drifting in a semiconductor material exhibiting either positive or negative differential mobility.     

Inverse scattering of dielectric cylinders by a cascaded TE-TMmethod

A novel approach for inverse scattering of dielectric objects Is proposed. This reconstruction algorithm aims to synthesize individual TE and TM inverse scattering in order to decrease the effect of ill-posedness. The proposed synthesizing method has a cascade structure composed of TE and TM inverse scattering algorithms. Appropriate approaches are adopted in these two algorithms to take advantage of the physical difference between them. A diversity scheme of multiple incident views and receiving points is also incorporated. Numerical simulations are conducted to compare the proposed synthesizing method with two other methods using individual TE or TM information. Some advantages of the synthesizing method are also observed     

Intersubband relaxation of hot carriers in coupled quantum wells

We compare experimental results for the photoluminescence decay in coupled quantum wells with a Monte Carlo simulation of electron and hole dynamics in this structure. The results support the assumption that the measured decay is associated with intersubband relaxation of electrons with little effect due to the holes. Quantitative agreement is found between the measured and theoretical time constants for most fields, although the theoretical values are shorter than the corresponding experimental values close to resonance.     

半导体纳米颗粒载流子的超快弛豫过程

分析了纳米颗粒的能级结构,建立了载流子弛豫的简化模型,运用数值模拟方法讨论了激发密度、表面态密度及俘获态电子的弛豫率对弛豫过程的影响。讨论结果表明,激发密度的增大及表面态的减少都会导致表面态上电子的饱和,使导带上出现电子的积累,导带电子寿命增大;深俘获态电子的弛豫是影响材料响应速度的主要因素。最后应用此模型对近红外泵浦探测实验的结果进行分析,表明模型可望在实验结果分析上得到应用。     

Microwave hall field inertia due to dielectric relaxation time

The magnetoresistive e.m.f. caused by microwave was measured as a function ofωτ _m in wide (3 cm – 4mm) range wave length. It has been found that Maxwell relaxation time does not influence the microwave Hall field lag in semiconductors. The discussion of these results is presented.     

Determination of bulk trap parameters using thermal dielectric relaxation techniques

A new non-steady-state technique for determining the energy levels of traps through which electron-hole pairs are generated in the depletion-layer of the silicon of metal-oxide-silicon (MOS) capacitor structures has been applied to metal-nitride-oxide-silicon (MNOS) structures. The technique consists of cooling the device to low temperatures and biasing it into the deep-depletion mode. The temperature of the device is then raised at a constant rate and the resulting I_g-T characteristic exhibits a pronounced wide peak. The energy level of the traps involved in the generation process was obtained from the slope of the log_eI_g - 1/T plot of the leading edge of the I_g-T characteristic curve, and is found to be 0·55 eV.A cross-check on the trap levels involved in the generation process was made by performing the experiment at two heating rates, β₁ and β₂. From a knowledge of the corresponding temperatures at which the maxima of the two peaks in the I_g-T characteristics occur, the energy level of the traps was found to be 0·54 eV. Furthermore, having obtained the trap level, the so-called carrier lifetime, τ, was found to be approximately 4μ sec.Experiments are described which provide convincing evidence that the generation of electron-hole pairs occurs in the depletion-layer of the silicon rather than at the silicon-silicon interface.     

Hopping conductivity and dielectric relaxation in Schottky barriers on GaN

A study of the current and capacitance dependences on the forward voltage in Au/n-GaN Schottky diodes, the sub-band optical absorption spectra, and the defect photoluminescence in n-GaN bulk crystals and thin layers is reported. It is shown that defect-assisted tunneling is the dominant transport mechanism for forward-biased Schottky contacts on n-GaN. The dependences of the current and capacitance on forward bias reflect the energy spectrum of defects in the band gap of n-GaN: the rise in the density of deep states responsible for yellow photoluminescence in GaN with increasing energy and the steep exponential tail of states with an Urbach energy of E _U = 50 meV near the conduction-band edge. A decrease in the frequency of electron hops near the Au/n-GaN interface results in a wide distribution of local dielectric relaxation times and in a dramatic transformation of the electric-field distribution in the space-charge region under forward biases.     

基于BP神经网络的介质圆柱体逆散射方法研究

将人工智能技术应用于介质圆柱体电磁逆散射问题研究,通过BP神经网络将原逆散射问题转化为一个回归估计问题,重构了目标的几何与电磁参数。在TM波的照射下,设置多个目标散射场的观测点,以散射场的幅值作为BP网络的输入,相应的几何与电磁参数作为输出,经过适当的训练,建立了介质圆柱体逆散射模型,并以此模型重构了已知探测范围内的介质圆柱体的半径、相对介电常数及电导率。比较结果显示了该方法的有效性和准确性,为目标的实时逆散射研究提供了一种有效方法。     

基于支持向量机的介质圆柱体逆散射问题研究

提出一种新的在线逆散射方法-支持向量机,通过支持向量机将原问题转化成一个回归估计问题.该方法可广泛应用于各种逆散射方面,尤其是目标的几何与电磁参数重构.以相对介电常数作为输入,复散射系数作为输出,通过对训练样本的学习,利用支持向量机回归估计了介质圆柱体不同相对介电常数下复散射系数的实部与虚部.同时,以多个观测点的散射电场值作为样本信息,利用支持向量机对已知探测范围内的介质圆柱体的相对介电常数和电导率进行了重构.比较结果显示了该方法的有效性和准确性.     

Inverse obstacle scattering for homogeneous dielectric cylindersusing a boundary finite-element method

A method for reconstructing the shape and the permittivity of a penetrable homogeneous cylinder is described. It is the extension to penetrable cylinders of a previous work dealing with perfectly conducting cylinders. A low-frequency approximation is used to determine an initial guess. Then, a rigorous boundary integral method permits us to reconstruct arbitrary shapes and complex permittivities. It is based on an iterative conjugate gradient algorithm requiring the solving of two direct diffraction problems only. A simple and original regularization scheme is presented, which ensures the robustness of the algorithm. Numerical examples with lossy embedding media and additional random noise for both E∥ and H∥ polarizations are given     

Collective vibrational modes and dielectric relaxation of Ca2ErNbO6

The double perovskite oxide calcium erbium niobate, Ca₂ErNbO₆ (CEN) is synthesized by solid-state reaction technique. The Rietveld refinement of the room temperature X-ray diffraction pattern of the material shows that CEN is crystallized in the monoclinic P2₁/n crystal symmetry. Vibrational properties of the sample for P2₁/n symmetry are analysed using Raman and infrared spectroscopies. The dielectric relaxation and ac conductivity of CEN are investigated in the temperature range from 303 to 573 K and in the frequency range from 100 Hz to 1.1 MHz using impedance spectroscopy. Modified Cole–Cole equation is used to describe the relaxation phenomenon. The frequency dependent conductivity spectra follow the Jonscher power law. The values of Activation energy indicate that the dielectric relaxation and the conduction mechanism are due to adiabatic small polaron hopping of charge carriers. The complex impedance plane plot of the sample indicates the presence of both grain and grain-boundary effects and is analyzed by an electrical equivalent circuit consisting of resistances and constant-phase elements.     

The effect of transients on hot carriers

The influence of time-dependent voltages on hot-carrier generation in MOSFETS is studied by transient device simulation. For transient times down to the nanosecond range, no transient effects on hot-carrier formation and injection are found. This result is confirmed experimentally by substrate current measurements under various dynamic voltage conditions down to rise/fall times of 3 ns. This result has important consequences for the interpretation of dynamic stress data, since it means that device-related dynamic effects can be neglected in comparison with interface-related effects in transient ranges relevant to practical applications     

Electro-optic relaxation effect in ZnS

A relaxation effect in natural crystals of cubic ZnS, seen during d.c. measurement of the electro-optic coefficient at a wavelength of 0.6328 ?m, is explained in terms of photo-electrically induced space charge. The effect is not evident at low light levels, or at wavelengths remote from the absorption edge of this semiconductor material.     

Observation of level degeneracy effect on interactions between traveling waves

Measurements were made of the nonlinear interaction in a saturable absorber between two traveling waves of different planes of polarization. The experimental results indicate that the theory proposed by Dienes, which includes level degeneracies, correctly describes the nonlinear interaction.     

A study of relaxation current in high-/spl kappa/ dielectric stacks

Dielectric relaxation currents in SiO/sub 2//Al/sub 2/O/sub 3/ and SiO/sub 2//HfO/sub 2/ high-/spl kappa/ dielectric stacks are studied in this paper. We studied the thickness dependence, gate voltage polarity dependence and temperature dependence of the relaxation current in high-/spl kappa/ dielectric stacks. It is found that high-/spl kappa/ dielectric stacks show different characteristics than what is expected based on the dielectric material polarization model. By the drain current variation measurement in n-channel MOSFET, we confirm that electron trapping and detrapping in the high-/spl kappa/ dielectric stacks is the cause of the dielectric relaxation current. From substrate injection experiments, it is also concluded that the relaxation current is mainly due to the traps located near the SiO/sub 2//high-/spl kappa/ interface. As the electron trapping induces a serious threshold voltage shift problem, a low trap density at the SiO/sub 2//high-/spl kappa/ interface is a key requirement for high-/spl kappa/ dielectric stack application and reliability in MOS devices.     

Anomalous effect of carriers on dielectric constant of (In,Ga)(As,P) lasers operating at 1.3 ?m wavelength

Injected carriers were found to reduce the dielectric constant of the active layer by the unexpectedly high value of 0.4. This is a factor of approximately four greater than measured for GaAs/(Ga, Al)As lasers and also higher than other reported values for (In,Ga)(As,P) lasers operating at a wavelength of 1.6 ?m. The technique employed was the observation of the spectral shift of individual Fabry-Perot modes of oxide insulated stripe lasers down to very low currents below threshold.     

Picosecond relaxation of band-gap renormalization induced by the Coulomb interaction of charge carriers in GaAs

The dynamics of the long-wavelength edge of the spectrum of intrinsic stimulated picosecond emission occurring upon the picosecond pumping of GaAs is studied experimentally. The shortage of bandgap renormalization induced by the Coulomb interaction of charge carriers, compared to renormalization in the quasi-steady state, is observed. It is conceived that the shortage is caused by the fact that, under the experimental conditions of the study, the renormalization relaxation time is in the picosecond region.     

Microwave-induced auditory effect in a dielectric sphere

The acoustic pressure wave generation inside an electromagnetically lossy dielectric sphere from an incident microwave pulse is analyzed rigorously. The pressure wave equation derived using the first-order approximation of a thorough formulation on microwave-induced thermoacoustic effect in dielectrics, is used. The inhomogeneous hyperbolic-type pressure wave differential equation is solved by a Green's function theory approach. The boundary conditions on the dielectric sphere-air interface are taken into account. The power is computed by applying the exact Mie theory solution for the dielectric sphere. Two types of acoustic waves are derived inside the sphere: (a) a transient burst type pressure wave, corresponding to the free-space contribution of Green's function; and (b) an infinite set of damped oscillations related to the normal acoustic modes of the spherical resonator. Numerical results are computed and presented for several cases     

激光诱导紫铜等离子体过程中的逆韧制辐射效应

为了研究激光等离子体相互作用过程中逆韧制辐射效应,用1064nm Nd:YAG激光器诱导产生紫铜等离子体,建立3条铜原子谱线的Boltzmann图,计算得到紫铜等离子体的电子温度为6902K。通过测量铜原子谱线324.75nm的Stark展宽,计算得到紫铜等离子体的电子密度为3.6×1017cm-3;基于铜等离子体的特征参量,得到紫铜等离子体的逆韧制辐射系数是0.021cm-1。结果表明,该光谱分析方法可以在避免对等离子体产生扰动的情况下,得到等离子体的特征参量。