Ⅰ类超晶格势阱中能级分布及电子跃迁规律研究

在研究大量实验曲线的基础上,指出势阱所有能级均有一定的宽度,电子或空穴在各能级中出现的概率符合正态分布,从理论上分析了I类超晶格和双势垒单势阱的发光光谱与吸收光谱·解释了GaAs/Ga1-xAlxAs多量子阱和超晶格吸收光谱吸收边及量子阱变窄时各吸收峰的“蓝移现象”及GaAs/Ga1-xAlxAs双势垒单量子阱样品的电流—电压特性曲线及电导—电压特性曲线的特征和出现的“负阻效应”·     

弱耦合GaAs/AlGaAs/InGaAs双势阱隧穿结构的磁隧穿特性研究

研究了低温(15 K)条件下弱耦合GaAs/AlGaAs/InGaAs双势阱结构的纵向磁隧穿特性. 研究表明,器件在零偏压下处于共振状态. 通过分析不同偏压下的磁电导振荡曲线,可以得到双量子阱中的基态束缚能级随偏压的变化规律,从而可以确定隧穿电流峰对应的隧穿机制. 所得结果可为弱耦合双量子点器件的制备提供基础. 关键词： 双量子阱 隧穿结构 磁电导振荡     

AlGaAs/GaAs多量子阱结构中受激载流子的飞秒弛豫特性

本文介绍采用飞秒饱和吸收测量技术研究Al_xGa_(1-x)As/GaAs多量子阱结构中受激载流子的超快弛豫特性.当激发光子能量大于样品势垒层能带隙时,受激产生于势垒层和势阱层连续态中的载流子分别在130和30fs时间内离开受激态,弛豫至准平衡态.势垒中的载流子被捕至势阱束缚态的情况主要发生于热载流子的冷却和复合过程的皮秒级时间内.     

半导体超晶格子带间跃迁光吸收理论研究

从理论上研究了半导体超晶格子带间跃迁的光吸收性质，以GaAs/AlxGa1－xAs超晶格为例进行数值计算，分析了该材料的吸收系数随入射光光子能量、光场强度和超晶格结构参量（阱宽，垒宽，势垒高）的变化关系计算表明：随着入射光光子能量的变化，出现非对称的吸收峰；光强只改变吸收系数大小；超晶格结构参量会改变吸收谱的谱宽和吸收峰所对应的入射光频率随着超晶格阱宽（垒宽）的增大，吸收谱由宽变窄，吸收峰红移；随着超晶格Al组分变大，吸收谱变窄.     

GaAs/AlGaAs多量子阱光生电压谱研究

在18—300K温度范围内,研究了用半绝缘体GaAs作为衬底的GaAs/AlGaAs多量子阱的光生电压谱.共观测到11H,11L,22H,22L,33H,33L,13H和31H等多种允许和禁戒的激子吸收峰.低温下的光生电压谱清晰地反映了多量子阱台阶式的状态密度分布.认为光生电压谱也可以作为一种判断多量子阱和超晶格外延生长质量的方法.还讨论了光生电压随温度的变化和光生电压效应的机理. 关键词：     

能级填充对量子阱光学性质的影响

在特殊设计的三势垒双势阱结构中，利用来自发射极的电子注入和电子向收集极的共振隧穿 逃逸调控量子阱不同子能级上的填充状态，发现激发态上的电子占据起抑制量子限制Stark 效应的作用.在极低偏压下，量子阱中少量过剩电子诱发了用简单带—带跃迁无法解释的光致发光光谱行为. 关键词： 共振隧穿 光致发光 量子限制Stark效应 过剩电子     

混合金属卤化物的超晶格与量子线特征

从紧束缚模型出发,发现周期性排列的两种金属卤化物材料可以形成超晶格和多量子阱(线)结构,并进一步研究了这种新型结构的性质随单体材料势垒和势阱宽度的变化规律,发现由金属卤化物形成的周期性结构表现出明显的量子阱(线)特征,对掺杂电荷的约束作用也非常强,从而证明了可以研制和开发基于金属卤化物的多量子阱(线)材料与器件. 关键词： 超晶格 量子阱 金属卤化物     

“W”型势阱能级的对比研究

通过有限差分法及Matlab矩阵运算,计算了阱区分别呈抛物形(WⅠ型)和三角形(WⅡ型)的两种"W"型一维势阱的能级.计算结果表明,在中间势垒(Vb)值固定情况下,两型势阱中各能级值随着边势垒(V0)的增大而增大,能级分裂先从较高能级开始,然后逐渐演变到较低能级,同能级比较,WⅡ型出现分裂较WⅠ型早.相反的变化趋势出现在V0固定、而Vb逐渐增大和V0、Vb同步增大的情况下.WⅠ型势阱最小的两能级随V0/Vb的变化表现稳定;在势垒相同情况下,WⅡ型各能级值较WⅠ型大,说明WⅠ型两阱具有比WⅡ型更强的耦合作用.本文的研究可为双量子阱器件的能带设计提供理论参考.     

对称GaAs/Al0.3Ga0.7As双量子阱中激子的束缚能

在有效质量近似下采用简单的尝试波函数变分地计算了对称GaAs/Al0.3Ga0.7As双量子阱中激子体系束缚能,研究了体系束缚能随阱宽和垒宽的变化情况.发现双量子阱中激子体系束缚能随阱宽变化同单量子阱情况类似,但束缚能的峰值出现在阱宽为10(A)左右,峰值位置小于单阱的情况;束缚能随垒宽的增加有一极小值,这与波函数向垒中的渗透有关.     

引入反比相关双曲余弦平方势描述超晶格量子阱的电子跃迁

 鉴于“方形”势阱过于简单和理想，引入了反比相关双曲余弦平方势描述超晶格量子阱中的电子运动行为。在量子力学框架内，把电子的Schrodinger方程化为了超几何方程, 并以Ga^1-xAl^xAs-GaAs- Ga^1-xAl^xAs量子阱为例计算了电子的带内跃迁和带间跃迁。结果表明，能级数目和跃迁能量与阱深、阱宽等系统参数有关，只需适当调节这些参数就可望实现对超晶格量子阱光电特征的调节与控制。     

Linear and nonlinear intersubband optical absorption in symmetric double semi-parabolic quantum wells

The linear and the nonlinear intersubband optical absorption in the symmetric double semi-parabolic quantum wells are investigated for typical GaAs/AlxGa1−xAs. Energy eigenvalues and eigenfunctions of an electron confined in finite potential double quantum wells are calculated by numerical methods from Schrödinger equation. Optical properties are obtained using the compact density matrix approach. In this work, the effects of the barrier width, the well width and the incident optical intensity on the optical properties of the symmetric double semi-parabolic quantum wells are investigated. Our results show that not only optical incident intensity but also structure parameters such as the barrier and the well width really affect the optical characteristics of these structures.     

Polaronic effects on the energy levels of a double donor impurity in quantum wells in the presence of a magnetic field

In the presence of a magnetic field the Hamiltonian of the single or double polaron bound to a helium-type donor impurity in semiconductor quantum wells (QWs) are given in the case of positively charged donor center and neutral donor center. The couplings of an electron and the impurity with various phonon modes are considered. The binding energy of the single and double bound polaron in Al_xlGa _1-xlAs/GaAs/Al_xrGa _1-xrAs QWs are calculated. The results show that for a thin well the cumulative effects of the electron-phonon coupling and the impurity-phonon coupling can contribute appreciably to the binding energy in the case of ionized donor. In the case of neutral donor the contribution of polaronic effects are not very important, however the magnetic field significantly modifies the binding energy of the double donor. The comparison between the binding energies in the case of the impurity placed at the quantum well center and at the quantum well edge is also given. Received 16 February 1999     

双量子阱中的子带光吸收

由于微制造技术的不断发展,如液相外延(LPE),气相外延(VPE),金属有机化学气相沉积(MOCVD)以及分子束外延技术(MBE)等先进的材料生长技术方法也日趋完善,从而使得各种低维半导体量子器件(如半导体、超晶格、量子阱、量子线和量子点等)制造日趋成熟。由于这些低维半导体量子器件具有很强的非线性光效应,而且随着材料、外形、尺寸等的不同,非线性光效应也有很大的差别,更由于其可能存在的广泛的应用前景,所以近年来,一直是人们研究的重点。近来,由于人们相信,利用GaAs／AlGaAs量子阱有可能制造出一些新型的光学仪器,如光开关、光限幅器、光调制器等,所以,对不同势形的GaAs／AlGaAs量子阱的非线性光学特性一直吸引着人们进行理论和实验的研究。而在最近几年,对双量子阱的研究也成为了人们的研究重点。通过密度矩阵和迭代的方法,得到双量子阱中的第一、第三阶子带光吸收表达式,我们将用一个典型的GaAs／AlGaAs双量子阱代入其中进行数值计算,并进行讨论。我们的计算结果显示,阱的光吸收峰不但与中间的势垒宽度有关,更与入射光强有关。     

Effect of interdiffusion on the band structure and absorption coefficient of a one-dimensional semiconductor superlattice

The effect of interdiffusion of Al and Ga atoms on the confining potential, band structure and absorption coefficient of electromagnetic radiation of a one-dimensional superlattice, composed of GaAs/Ga_1?x Al _x As quantum wells with the initially rectangular potential profile, is studied within the framework of the modified Wood-Saxon potential model. It is shown that the interdiffusion leads to the widening of the energy minibands and to the blueshift of the absorption spectrum observed in experiments.     

GaAsN/AlAs/AlGaAs double barrier quantum wells grown by molecular beam epitaxy as an alternative to infrared absorption below 4 μm

In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed.     

Linear and nonlinear optical absorption coefficients in inverse parabolic quantum wells under static external electric field

In the present theoretical study, the linear and third-order nonlinear optical absorption coefficients have been calculated in GaAs/Ga_1−x Al _x As inverse parabolic quantum wells (single and double) subjected to an external electric field. Our calculations are based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, as quantum well width, quantum barrier width, Al concentration at each well center and magnitude of the external electric field. Our results indicate that in most cases investigated, the increase of the electric field blue-shifts the peak positions of the total absorption coefficient. In all cases studied it became apparent that the incident optical intensity considerably affects the total absorption coefficient.     

Structures of energy spectrum and persistent currents in mesoscopic rings with radial potential barrier in magnetic field

The energy spectrum and the persistent currents are calculated for finite-width mesoscopic annular structures with radial potential barrier in the presence of a magnetic field. The introduction of the tunneling barrier leads to the creation of extra edge states around the barrier and the occurrence of oscillatory structures superimposed on the bulk Landau level plateaus in the energy spectrum. We found that the Fermi energy E _F increases with the number of electrons N emerging many kinks. The single eigenstate persistent current exhibits complicated structures with vortex-like texture, “bifurcation”, and multiple “furcation” patterns as N is increased. The total currents versus N display wild fluctuations.     

Improvement in intersubband optical absorption and the effects of device parameter variations in quantum wells with an applied electric field

The intersubband optical absorption in symmetric and asymmetric, single and coupled, double GaAs/ Ga_{1 − x}Al_xAs quantum wells is calculated. The results have been obtained in the presence of a uniform electric field as a function of the potential symmetry, size of the quantum well, and coupling parameter of the wells. In coupled double quantum wells we obtain a large Stark effect that can be used to fabricate tuneable photodetectors. We show that the effect of an applied electric field on the intersubband optical absorption is similar to changes in the dimensions of the structure. This behaviour in the intersubband optical absorption for different wells and barrier geometries can be used to study these systems in regions of interest, without the need for the growth of many different samples.     

对于“包含在连续谱量子体系中的决定论性”一文的讨论

对于具有连续能谱的单粒子量子体系,“包含在连续谱量子体系中的决定论性”一文用所谓“双波函数”来描述处于能量本征态的粒子系综中各粒子的量子行为,并且在所谓的“等价定理”中称:双波函数描述在经典极限下将化为经典力学描述.然而,此描述所给出的系综力学量观测值统计分布的预言与通常量子力学不相容;并且,该文对其“等价定理”的证明是不正确的,这个“定理”实际上不成立 关键词： 连续能谱量子体系 双波函数 经典极限