非接触四波混频技术测试InP单晶

利用四波混频(FWM)技术测试了非掺杂、掺Fe半绝缘InP单晶的光电特性,对载流子的产生、复合和输运等过程进行了研究,分析了深陷阱在载流子的产生与输运中的作用,并给予了解释。利用光栅衰减动力学得到在不同激发水平下非平衡自由载流子的扩散系数和复合时间。通过分析衍射效率和激发能量之间的相互关系,测定了缺陷的电学特性,即它们在光照下的传输和对载流子传输的贡献。这种技术可以通过测量时间和空间上的载流子分布,进而利用光学技术测试半导体材料的光电特性。     

RBa_2Cu_3O_（7－δ）（R＝Y，Pr）薄膜中非平衡载流子的超快弛豫动力学

通过拟合ＹＢａ２Ｃｕ３Ｏ（７－δ）（δ＝０．１，０．４，０．８）和ＰｒＢａ２Ｃｕ３Ｏ７外延膜的室温飞秒瞬态反射谱，研究了其非平衡载流子的超快弛豫动力学，计算了电声耦合常数λ．发现随着氧含量的降低及用Ｐｒ替代Ｙ，Ｃｕ－Ｏ面上载流子浓度降低，非平衡载流子的弛豫时间增加而电声耦合常数明显减小．这表明电声耦合与载流子浓度的依赖关系，电声相互作用可能是一种实空间局域相互作用．     

In_xCa_(1-x)As/GaAs应变量子阱结构中热载流子分布的皮秒光谱研究

用皮秒时间分辨荧光相关技术研究了In_xGa_(1-x)As/GaAS应变量子阱中的热载流手弛豫过程,结果表明,In组分x值(不同应变)对载流子弛豫寿命有明显的影响;与体材料相比,热载流子分布弛豫过程明显变慢,寿命明显增加.     

半导体中非平衡载流子的输运过程(Ⅰ)

在描述载流子输运过程的玻尔兹曼方程的碰撞项中考虑了带间跃迁的贡献,从而将它推广到存在非平衡载流子的情况。由此导出了非平衡载流子寿命,复合几率的统计表达式,以及包括产生-复合过程的电荷连续性方程和稳态输运过程的电流方程。     

量子点激光器瞬态响应及调制特性分析

基于二能级系统建立量子点激光器的载流子-光子速率方程模型,分析量子点激光器的瞬态响应和调制特性,获得其动态特性.同时分析了注入电流对量子点激光器输出光子密度的影响,随着注入电流的增大,激光器光电延迟时间缩短,弛豫过程缩短,弛豫振荡频率增大,且输出光子峰值和稳态功率增加,适当增加注入电流可拓宽量子点激光器调制带宽.通过小信号调制分析,发现量子点激光器上限调制频率比普通激光器高一个数量级,证明了其具有良好的高频调制特性.     

多量子阱半导体激光器的瞬态响应特性分析

根据光增益与载流子密度的对数关系,在受激发射速率中分别引入了增益饱和项和载流子复合项,通过适应于多量子阱激光器的速率方程,从理论上证明了短腔结构存在与阈值电流最小值对应的最佳阱数。给出了多量子阱激光器的瞬态呼应特性的直接仿真结果及相图,分析了注入电流、阱数和腔长对其激射阈值、开关延误时间、弛豫振荡频率和光输出等能量的影响。     

（英）中红外量子级联激光器输运特性的仿真

基于一种非局域化的输运模型,对不同结构不同温度下的中红外量子级联激光器的输运特性进行了仿真。在这个模型中,利用量子隧穿、微带隧穿以及热载流子输运等长程载流子输运模型,对传统的扩散-漂移方程进行了矫正.并将基于上述集成模型的计算结果和实验结果进行了比较,通过拟合参数的合理设置,计算结果和实验结果得到了很好的吻合.     

量子阱带间跃迁探测器基础研究（特邀）

在最近的实验中,PN结型量子阱结构被观察到反常的载流子输运情况,其相应的物理机制和载流子输运模型被提出。通过系统实验观察到,PN结量子阱结构材料在共振激发模式下,仍可测出开路电压或短路电流。对比开路和短路情况下的光致荧光（PL）光谱,发现短路下PL强度明显降低。这说明短路状态下的光生载流子没有被限制在量子阱内,而是逃逸出结区。这种载流子逃出量子阱的现象却没有在等量偏压下的NN型量子阱结构中发现,说明载流子逃出量子阱并非由传统的热激发或隧穿的作用导致。据此,笔者提出了相应的物理机制和载流子输运模型对此现象进行解释,认为光生载流子能在PN结内建电场的作用下直接逃出量子阱,并且辐射复合发光发生在载流子逃逸过程之后。     

长波带间级联探测器结构设计

针对带间级联结构在长波探测上的设计应用,采用包络函数近似下的二带模型和传输矩阵方法,考虑电子和轻空穴耦合,计算了带间级联结构多量子阱弛豫区的E-k关系和详细能带信息.特别优化了弛豫区结构,在保证光生载流子在弛豫区中隧穿几率的前提下首次利用周期性量子阱结构拓展弛豫区厚度,降低吸收区中电场强度,抑制产生复合电流和隧穿电流,提高器件电学性能.制备的该两级结构长波带间级联探测器10. 5μm处量子效率达到了20%,证实了弛豫区与隧穿区具有良好的光生载流子输运.器件在80 K下50%截止波长为11. 5μm,是目前所见报道中带间级联结构在80 K工作温度下所获得最长波长的红外探测器.     

半导体技术

TN3OI 01050443InAs/GaAs低维结构中载流子快速俘获过程的研究/李晴,徐仲英,葛惟昆(中国科学院半导体所)即红外与毫米波学报一2000,19(5)一343一346用简并激发一探测技术研究了77K温度下InAs/GaAs量子点中载流子快速俘获和弛豫过程.在瞬态反射谱测量中,除观察到一与G aAs有关的弛豫过程外(时间常数约为1 ps),还观察到一个时问常数为几个至ZOPs的反射率上升过程.提出了一个物理模型,表明匕述上升过程与光致载流子被InAs层快速俘获过程有关,并由此得到载流子的俘获时间,俘获时间随载流子浓度增加而减小.图3参12(李)2(许)TN3OI 01050…     

Simulation of ultrafast relaxation of photoexcited electrons via analytical distribution functions

We propose an analytic representation to study electron relaxation during an ultrafast process in a semiconductor quantum well. Gauss-type energy functions are used to simulate the peaks of nonthermal electrons, while the background electrons are described by a Boltzmann distribution function. The time variations of parameters describing the amplitudes and widths of Gauss-type functions, and the temperature of background electrons, are determined by solution of the Boltzmann equation with electron-electron and electron-phonon interactions.     

Picosecond spectroscopy of semiconductors

The time-resolved reflectivity of picosecond pulses from optically excited carrier distributions can provide important information about the energy relaxation rates of hot electrons and holes in semiconductors. The basic optical properties of non-equilibrium carrier distributions are discussed, and in the specific case of GaAs, a semi-empirical analysis of the reflectivity spectrum is described which estimates the contributions from the principal critical points of the band structure. Using Boltzmann factors to approximate the hot carrier distributions, it is found that the non-equilibrium reflectivity spectrum is a sensitive function of carrier temperature and that it can reverse its sign as the distribution relaxes. These results are in good qualitative agreement with recent experiments employing a mode-locked cw dye laser.     

Picosecond optical studies of 2D electron - 2D phonon dynamics

We describe recent developments in time-resolved optical measurements of electron-phonon interactions in quantum wells which reveal the fundamental two-dimensional properties of the process. Picosecond photoluminescence experiments show enhanced energy relaxation in narrow quantum wells. Time-resolved Raman measurements of inter- and intra-subband relaxation of electrons reveal the participation of confined optical phonons; in narrow quantum wells there is strong coupling to interface phonons.     

Hot-carrier dynamics in Ge on single picosecond timescales: Comparing Raman and reflectivity experiments with a self-consistent kinetic model

Through comparisons of picosecond Raman and transient reflection experiments with a comprehensive kinetic model of photo-excited carrier and lattice dynamics in Ge, we demonstrate the ability of these techniques to probe subtle aspects of non-equilibrium carrier dynamics in group IV materials at moderate injected carrier densities. Using material parameters taken from the literature, the temporal evolution of the non-equilibrium optical phonon population generated by the relaxation of photo-excited electrons and holes is obtained by solving a coupled set of Boltzmann equations for the electron and hole particle and thermal currents. The results of the calculation agree, in absolute terms, with the experimentally observed evolution of the non-equilibrium optical phonon population. The calculation also predicts that the hot plasma initially diffuses rapidly away from the sample surface, on a 5 picosecond timescale, and subsequently diffuses much slower as the carrier temperature decays to the lattice temperature, and the density gradient diminishes due to the hot carriers which have already migrated into the material. This prediction is verified by comparison of the calculated change in reflectivity due to the plasma, and picosecond reflectivity measurements performed at room temperature with 575 nm pulses.     

Physical Foundations of Formation of Bio-Self-Organization and the Bio-Photon Emission in the Living Systems

According to elementary processes of the biological activities in the living systems with open and non-equilibrium states, which can ever exchange the energy and material and information with the environments, we have established a statistical model formed bio-self-organization, which live on the basis of the negative entropy, by the quantum statistical-theory of non-equilibrium state. From this model we have obtained the peculiar curves of changes of the energy of molecules and found out the distribution function of bio-molecules on quantum energy-levels in the living systems which are completely different from that in inorganic matters. Utilizing the curves of energy obtained we explain well the phenomenon of bio-photon emission of the bio-self-organizations found in the experiments.     

Hot carriers in quasi-2-D polar semiconductors

This paper reviews hot carrier effects in quasi-2-D polar semiconductors (quantum wells and heterostructures), with special emphasis on the GaAs/AlGaAs system. After briefly introducing the basic concepts in hot carrier physics, we discuss theoretical calculations of carrier-phonon interactions and hot carrier energy loss rates to the lattice in quasi-2-D systems. We then discuss how these quantities are affected by degeneracy, plasma effects, and hot phonons. The bulk of the paper is devoted to a discussion of experimental results and their analysis. Three kinds of experiments are discussed: I-V and related transport measurements, direct time-of-flight measurements of velocity-field characteristics, and measurements which use optical spectroscopy to provide direct information about the carrier distribution function in the presence of external perturbations. The optical studies have given valuable new insight into the behavior of hot carrier relaxation processes in quasi-2-D systems from femtosecond to steady-state conditions.     

Carrier energy relaxation time in quantum-well lasers

Carrier energy relaxation via carrier-polar optical phonon interactions with hot phonon effects in multisubband quantum-well structures is theoretically studied by using both bulk longitudinal optical phonons and confined longitudinal optical phonons. We find that the width and the depth of quantum wells only have moderate effects on carrier energy relaxation rates. Our results also indicate that the difference of energy relaxation rates between the quantum well and the bulk material is not significant. We investigate the effects of longitudinal optical phonon lifetimes on the carrier energy relaxation rate. Neglect of the finite decay time of longitudinal optical phonons will significantly underestimate the carrier energy relaxation time; this not only contradicts the experimental results but also severely underestimates the nonlinear gain coefficient due to carrier heating. The implications of our theoretical results in designing high-speed quantum-well lasers are discussed     

Experimental realization of a new transistor

The authors report on the fabrication and characteristics of a unipolar, three-terminal, resonant-tunneling transistor. The operating principle of this new transistor is based on the fact that the quantum mechanical resonant-tunneling probability of hot electrons between the emitter and the collector is switched almost completely on and off, when either the base or the collector bias is swept. The emitter injects hot electrons to the second lowest subband of a thin (100 Å in this work) GaAs quantum well. Subsequently, the hot electrons will either resonantly tunnel to the collector, or relax to the lowest subband and contribute to the base current. As a result of resonant transmission, at 77 K the current-voltage characteristics of the transistor display negative differential resistance with extremely large (4691) peak-to-valley ratio. Furthermore, when biased near resonance, a maximum DC current gain of ~1.2 and a maximum AC current gain of ~11.9 were observed. The first use of a new `tunneling-in and tunneling-out' scheme in contacting a thin quantum well is also demonstrated     

Inelastic scattering of hot electrons by neutral donors in heavily silicon-doped GaAs/AlAs quantum wells

The energy and momentum relaxation of hot electrons in n-type GaAs/AlAs quantum wells is studied. Hot photoluminescence due to the recombination of hot electrons with holes bound on Si acceptors is observed in structures with a high level of doping with silicon. Using the method of magnetic depolarization of hot photoluminescence, the probability of scattering of hot electrons is found to decrease substantially with increasing temperature in the range 4–80 K. This effect is shown to be due to the ionization of donors. It is established that the probability of inelastic scattering by neutral donors is several times greater than the probability of quasielastic electron-electron scattering. Fiz. Tekh. Poluprovodn. 33, 1235–1239 (October 1999)