Effect of the electron and phonon mutual drag on the thermomagnetic and thermoelectric phenomena in conductors with degenerate carrier statistics

The transport coefficients of conductors with degenerate carrier statistics in a magnetic field have been calculated with the inclusion of the mutual electron and phonon drag. The calculation is carried out in the linear approximation in the degeneracy parameter. A study has been made of the mutual drag on the thermomagnetic and thermoelectric phenomena in conductors, in both isothermal and adiabatic conditions.     

掺金单晶硅特性的研究

本文研究单晶硅掺金前后的表面光伏和红外吸收谱,证实在相同表面状况下,红外吸收谱的基线与少子扩散长度的对应关系;由半导体统计,推导出简并因子不等于1时扩金硅的统计公式,以及金受主简并因子g_Au,a≠1,金施主简并因子g_Au,d≠1硅双重能级复合理论公式,由此计算的少子寿命值与测量值之比在1.64—0.745之间。 关键词：     

Self-focusing of electromagnetic waves in a degenerate electron-hole plasma

The free carrier nonlinear dielectric constant of a degenerate electron-hole plasma (e.g., Ge) in the presence of a Gaussian electromagnetic beam has been studied by a kinetic treatment. The redistribution of carriers (electrons and holes) is the source of nonlinearity and is effective in causing the self-focusing of the beam. The rise in carrier temperature due to the wave field is almost unaffected by the degeneracy, whereas the nonlinearity is considerably affected by it. The increase of degeneracy (by increasing the equilibrium carrier concentration at the fixed lattice temperature) increases the nonlinear dielectric constant. Hence self-focusing is enhanced by degeneracy. This work was supported by NSF (USA) and CSIR (India).     

Combined continuum-atomistic modeling of ultrashort-pulsed laser irradiation of silicon

Ultrafast thermomechanical responses of silicon thin films due to ultrashort-pulsed laser irradiation were investigated using an atomic-level hybrid method coupling the molecular dynamics and the ultrafast two-step energy transport model. The dynamic reflectivity and absorption were considered, and the effects of laser fluence and pulse duration on the thermomechanical response were studied. It was found that both the carrier temperature and number density rapidly increase to their maximum while the lattice temperature rises at a much slower rate. The ultrafast laser heating could induce a strong stress wave in the film, with the maximum compressive and tensile stress occurring near the front and back surfaces, respectively. For laser pulses of the same duration, the higher the laser fluence is, the higher the carrier temperature and density and lattice temperature are induced. For the same laser fluence, a longer pulse generally produces lower carrier density and temperatures and weaker stress shock strength. However, for the fluence of 0.2 J/cm², the lowest lattice temperature was simulated for a 100-fs pulse compared to the 1-ps and 5-ps pulses, due to the increase of reflectivity by high carrier density. It is also shown that the optical properties as functions of lattice temperature usually employed are not suited for modeling ultrafast laser interactions with silicon materials.     

飞秒激光辐照下单晶硅薄膜中超快能量输运的数值模拟

利用载流子输运模型对飞秒激光辐照下单晶硅亚微米薄膜中的能量输运过程进行数值模拟。研究了不同辐照能量密度和不同激光波长对载流子密度和温度超快变化过程的影响规律。结果表明,在800nm激光辐照下,不同入射能量密度仅影响载流子密度和温度响应的峰值,但达到峰值的时刻不变。平衡态的恢复过程受入射能量密度影响很小。在不同波长激光辐照下,光子能量越大,载流子密度和温度达到峰值所用时间越短,对应峰值越大,但衰减速度也越快。当入射光子能量大于单晶硅的直接带隙时,快速衰减时间常数可以与载流子能量弛豫时间相当。     

调制自由载流子吸收测量半导体载流子输运参数的三维理论

推导出用于测量半导体载流子输运特性(载流子寿命、载流子扩散系数和前表面复合速度)的调制自由载流子吸收(modulated free carrier absorption, MFCA)检测技术的三维理论模型,给出了调制自由载流子吸收检测信号与调制频率和抽运-探测光相对距离的关系.定性分析了在不同调制频率时各个载流子输运参数对径向位置扫描曲线(信号与两束光相对距离的关系)的影响,结果表明调制自由载流子吸收检测信号对各个参数的灵敏度随抽运-探测光相对距离的增加而增加.仿真和实验结果表明,通过拟合不同调制频率时调 关键词： 调制自由载流子吸收 载流子输运特性 径向位置扫描     

激光模简并解除及频差理论分析

本文介绍了激光模简并解除的实验观察和模简并解除的原因。利用激光器的兰姆理论详细分析和计算了单模和多模运转时模简并解除后的频差,并给出了频差随腔调谐频率变化的曲线。 关键词：     

Effect of electrically degenerated layer on the carrier transport property of ZnO epitaxial thin films

ZnO films were prepared on (1 1 1) YSZ and (0 0 0 1) sapphire by pulsed laser deposition method. Effect of lattice mismatch on the carrier transport properties of ZnO epitaxial thin films was investigated. The carrier mobility of the ZnO films on YSZ was larger than that of ZnO/sapphire due to smaller lattice mismatch when the thickness was below 150 nm. The effect of electrically degenerated layer on the carrier transport property increased with decreasing the film thickness of ZnO film. The carrier density and electron mobility of 20 nm-thick-ZnO film on either substrate were regardless of the temperature. We concluded that the dominant carrier scattering mechanism in ZnO ultra thin films is double Schottky barriers at the grain boundary and that their height depends on the carrier concentration.     

Influence of gain saturation and carrier dynamic models on the modulation response of quantum well lasers

The main problem for creation of optical communication systems is how quickly the light intensity can be changed under radiation from a laser diode. The modulation capability of lasers with separate confinement heterostructure depends strongly on carrier transport and gain saturation phenomena. Nonlinear gain saturation model in connection with dynamic behavior at high-frequency modulation is discussed and peculiarities of application of a new dynamic model with partial differential equation for the carrier transport in SCH region are shown.     

On the effective electron mass in quantum well wires of ternary chalcopyrite semiconductors

Summary An attempt is made to study effective electron mass in quantum well wires of ternary chalcopyrite semiconductors by formulating a new 1D dispersion relation, within the framework of thek·p formalism considering the anisotropies in the band parameters. It is found, taking quantum well wires ofn-CdGeAs₂ as an example, that the effective Fermi level mass depends on the subband index due to the combined influence of crystal-field splitting parameter and the anisotropic spinorbit splitting parameters, respectively. The masses increase with increasing carrier degeneracy and decreasing film thickness, respectively. In addition, the well-known results for the corresponding parabolic energy bands have been derived as special cases of the generalized formulations.     

Polarization instabilities in a two-photon laser

We describe the operating characteristics of a new type of quantum oscillator that is based on a two-photon stimulated emission process. This two-photon laser consists of spin-polarized and laser-driven 39K atoms placed in a high-finesse transverse-mode-degenerate optical resonator and produces a beam with a power of approximately 0.2 microW at a wavelength of 770 nm. We observe complex dynamical instabilities of the state of polarization of the two-photon laser, which are made possible by the atomic Zeeman degeneracy. We conjecture that the laser could emit polarization-entangled twin beams if this degeneracy is lifted.     

Change of the electron effective mass in extremely heavily doped n-type Si obtained by ion implantation and laser annealing

Infrared optical properties of extremely heavily doped n-type Si, obtained by ion implantation and laser annealing, were studied. A new relation between free carrier effective mass (m¹) and carrier concentration (10¹⁹ ?5 × 10²¹cm^-3) was obtained. The value of m¹ increases significantly with the increase of carrier concentration, when carrier concentration exceeds 10²¹cm^-3. The result is discussed in relation to the occupation of electrons in a new valley of the conduction band.     

波段外激光辐照光导型InSb探测器的一种新现象

利用不同功率密度的10.6 μm(光子能量为0.12 eV)连续激光辐照了禁带宽度为0.228 eV的光导型锑化铟探测器, 得到了与以往报道不同的实验现象. 当10.6 μm波段外激光辐照光导型探测器时, 探测器吸收激光能量后温度升高. 在探测器的温升过程中, 存在一个转变温度T₀. 当探测器的温度T<T₀时, 载流子浓度基本不变, 迁移率随温度的升高呈T^-2.35趋势下降, 引起探测器的电导率减小, 电阻增大, 响应输出电压升高; 当T>T₀时, 热激发载流子浓度随温度的升高呈指数增长, 电阻急剧下降, 超过了载流子迁移率降低对电阻的影响, 响应输出急剧下降. 光电导探测器在较高功率密度波段外激光辐照下的响应特性是载流子的浓度和迁移率在温度影响下相互作用的结果. 这对进一步完善半导体内载流子输运模型提供了实验依据.     

Two-electron and four-electron periodicity in single-wall carbon nanotube quantum dots

Single quantum dots have been fabricated in single-wall carbon nanotubes and electrical transport properties have been measured at low temperature. Two- and four-electron periodicities have been clearly observed in the same sample in different gate voltage ranges. The former is an even–odd effect which originates from the spin degeneracy, while the latter is related to the additional two-fold band degeneracy. The results are discussed with the energy scales associated with the dot, and the possibility for a single spin manipulation is suggested.     

Influence of degeneracy on momentum relaxation times in semiconductors

We have studied the effect of degeneracy on momentum relaxation times under ohmic as well as non-ohmic conditions. We find that a proper momentum relaxation time, within the framework of the Boltzmann transport equation, can no longer be defined for isotropic but inelastic scattering when the carriers are hot whereas under ohmic conditions it can be defined and is appreciably altered by degeneracy. For elastic scattering the momentum relaxation time is found to be unaffected by degeneracy for both ohmic and non-ohmic regimes.     

Energy and momentum relaxation of charge carriers in Ge and Si under uniaxial stress

Measurements of the piezoresistance and the energy relaxation time T_?, in Ge and Si under uniaxial stress up to 4 kb are reported in the temperature range 30 K < T < 300 K. The measurements of t_? have been performed in the warm carrier range using the harmonic mixing technique. The experimental results for the piezoresistance and energy relaxation time in n-type material can roughly be understood in terms of carrier redistribution in the conduction band valleys whose degeneracy is lifted by the stress. Information is obtained from these measurements about the relative strength of ? and g type intervalley scattering in n-Si; we find nearly equal coupling strength for both scattering types. For the p-type material the experiments show convincingly that the main effect of stress on transport quantities is also caused by the lifted degeneracy of the heavy and light hole bands, as predicted already by Adams, and by Pikus and Bir. The nonlinear dependence of the piezoresistance and τ_? on the stress can very well be explained by approximating the heavy and light hole bands as spherical and parabolical and using the deformation potential constant b as a parameter. The value of ≈2eV obtained for |b| is in good agreement with earlier results for p-Ge.     

Numerical simulation of the generation of gain switched laser pulses

Gain switched laser pulses with FWHM of 32 ps having an optical peak power exceeding 400 W are generated using low cost single heterostructure (SH) Fabry–Perot laser diodes. To examine and to optimize this effect in detail, a thorough physical device simulation is done. Maxwell's equations together with a simplified version of the Boltzmann transport equation (BTE) and various parameters like carrier recombination and material gain, form a coupled set of nonlinear, inhomogeneous partial differential equations, that are discretized using the finite difference scheme and solved selfconsistently.     

Seebeck coefficient of Ln<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> perovskites in paramagnetic state

The Seebeck coefficient is a function of carrier concentration and configurational entropy. In this report, we semi-theoretically investigate the Seebeck coefficient of Ln _x Ca_1−x MnO₃ (Ln=Rare-earth) perovskites based on the electronic structure of the 3d orbitals of Mn ions, using the developed Heikes model, Boltzmann transport model, and diffusion model. The results show that the Seebeck coefficient of such a strongly correlated electron system in paramagnetic state is remarkably affected by site degeneracy. As temperature decreases, the evolution of the spin and orbital degrees of freedom together with the change in phonon scattering mode describes the Seebeck coefficient behavior satisfactorily. The phonon drag effect at low temperature is also discussed.     

饮用水激光拉曼光谱的比较与分析

为了对我国目前饮用水的质量进行有效检测,对市面上几种常用品牌的饮用水以及实验室提供的蒸馏水等样品做了测量和计算。运用激光拉曼光谱的分析方法,测量了它们的激光拉曼光谱。同时,通过测量计算了样品在对称伸缩振动处拉曼谱的退偏度。结果表明,在水样品的对称伸缩振动处,其拉曼谱的相对强度大小和退偏度的大小有着相同的规律。对结果进行比较和分析后得出了如下结论：可以从拉曼光谱特征峰相对强度的大小和同一特征峰下退偏度的大小两方面来判断饮用水中矿物质含量的相对多少。为鉴定饮用水的质量提供了新的有效途径。