直接带隙Ge耦合双量子阱中的光吸收系数

在有效质量近似下,详细研究了直接带隙Ge/GeSi耦合双量子阱中带间光跃迁吸收系数和阈值能量随量子阱结构参数的变化情况。结果表明：随着量子阱阱宽增大,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象。增强耦合量子阱间的耦合效应使得带间光吸收强度显著提升。此外,与非对称耦合量子阱相比,耦合效应对对称耦合量子阱中光吸收系数的影响更为显著。     

直接带隙Ge耦合双量子阱中的光吸收系数

在有效质量近似下,详细研究了直接带隙Ge/Ge Si耦合双量子阱中带间光跃迁吸收系数和阈值能量随量子阱结构参数的变化情况.结果表明:随着量子阱阱宽增大,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象.增强耦合量子阱间的耦合效应使得带间光吸收强度显著提升.此外,与非对称耦合量子阱相比,耦合效应对对称耦合量子阱中光吸收系数的影响更为显著.     

加偏置电场的双曲线量子阱中线性与三阶非线性光学吸收系数的计算

利用紧致密度矩阵近似方法,研究了加偏置电场双曲线量子阱中的线性与三阶非线性光学吸收系数. 得到了该系统中的线性与三阶非线性光学吸收系数的解析表达式.分析了势阱的形状、外加电场的大小以及入射光场的强度对吸收系数的影响规律. 文章以典型的AlxGa1－xAs/ GaAs双曲线量子阱为例作了数值计算.结果表明：随着势阱宽度的增加,系统的吸收系数将减小;随着外加电场的增加,系统的非对称性增加,系统的吸收系数将增加;随着外加光场强度的增加,系统的吸收系数将减小,并且当光强增加到一定值时会出现明显的饱和吸收现象,这一结论为进一步的实验研究提供了相应的理论依据.     

有机量子阱的光学性质

采用多源有机分子气相沉积系统(OMBD)制备了Alq₃，PBD/Alq₃，PBD/Alq₃/PBD单层、双层以及量子阱结构，利用电化学循环伏安法和吸收光谱、荧光光谱研究了量子阱的类型和样品的光致发光特性.电化学循环伏安法和吸收光谱的测量结果表明，PBD/Alq₃有机量子阱为Ⅰ型量子阱结构.荧光光谱的研究结果表明，单层Alq₃的光致发光峰不随Alq₃厚度变化而变化；但是双层PBD/Alq₃结构光致发光峰随Alq₃厚度的减小而发生蓝移；同样对于PBD/Alq₃/PBD量子阱结构光致发光峰随Alq₃厚度的减小而发生蓝移.对引起光谱蓝移的原因进行了讨论. 关键词： 有机量子阱 光谱蓝移     

GaAs量子阱太阳能电池量子效率的研究

将量子阱结构引入到单结GaAs太阳能电池中能够有效扩展吸收光谱.为了研究量子阱结构在GaAs太阳能电池中的作用机理,本文采用实验和理论的方法研究了InGaAs/GaAsP量子阱结构对电池量子效率的影响.实验结果表明,量子阱结构的窄带隙阱层材料将电池的吸收光谱从890 nm扩展到1000 nm.同时,量子阱结构的引入提高了680—890 nm波长范围内的量子效率,降低了波长在680 nm以下的量子效率.通过计算得到的量子阱结构和GaAs材料的光吸收系数,可以用来解释量子阱结构对太阳能电池量子效率的影响.     

电场对量子阱中激子能级宽度的影响

本文把固体中较大窨范围运动的粒子作为准经典粒子来描述。将已导出的能量测不准公式和激子的经典力学模型应用到电场下GaAs/GaAlAs量子阱中,激子能级宽度的计算结果与测量结果基本吻合,能较清楚、简单地解释纵向电场和横向电场下激子光吸收线宽的很大的差异。     

电场对量子阱中强耦合磁极化子性质的影响

研究了量子阱中强耦合磁极化子在电场作用下的性质,采用线性组合算符及幺正变换的方法导出了强耦合磁极化子的振动频率λ和基态能量E₀.讨论了强耦合磁极化子的基态能量与阱宽、电场强度、回旋频率之间的关系.通过数值计算,结果表明:强耦合磁极化子的基态能量的绝对值随着阱宽的增加而减小,随着外加电场强度的增加而增加;磁极化子的基态能量的绝对值随着磁场的回旋频率的增加而增加;磁场的回旋频率随着磁极化子的振动频率的增加而增加.     

量子阱中二维电子气的性质

利用提出的三维不对称方势阱模型，对半导体量子阱中二维电子气的性质进行了研究，确定其量子能级和费米能量，并对有关结果进行了讨论。     

外电场对InGaAsP/InP量子阱内激子结合能的影响

在有效质量近似下采用变分法计算了InGaAsP/InP量子阱内不同In组分下的激子结合能,分析了结合能随阱宽和In组分的变化情况,并且讨论了外加电场对激子结合能的影响. 结果表明：激子结合能是阱宽的一个非单调函数,随阱宽的变化呈现先增加后减小的趋势;随着In组分增大,激子结合能达到最大值的阱宽相应变小,这与材料的带隙改变有关;在一定范围内电场的存在对激子结合能的影响很小,但电场强度较大时会破坏激子效应. 关键词： 激子 InGaAsP/InP量子阱 结合能 电场     

电场对量子阱中自由载流子光辐射线宽的影响

本文对固体中在较大空间范围运动的粒子采用轨道、动量及波包来描述。根据量子力学测不准关系, 粒子的能量测不准公式被导出。公式表明, 电场强烈地散射载流子, 使载流子所处能级大为展宽。应用该公式到Ｐ－Ｉ－Ｎ结构的ＧａＡｓ／ＧａＡｌＡｓ 多量子阱中, 理论计算的光辐射线宽与光致荧光实验测得的线宽吻合。     

Donor impurity states in direct-gap SiGe quantum well: Applied electric field and quantum size effects

Within the framework of the effective-mass approximation and variational procedure, competition effects between applied electric field and quantum size on donor impurity states in the direct-gap Ge/SiGe quantum well (QW) have been investigated theoretically. Numerical results show that the applied electric field (quantum size) dominates electron and impurity states in direct-gap Ge/SiGe QW with large (small) well width. Moreover, the competition effects also induce that the donor binding energies show obviously different behaviors with respect to electric field in the QW with different well widths. In particular, when the impurity is located at left boundary of the QW, the donor binding energy is insensitive to the variation of well width when well width is large for any electric field case.     

Band structure and impurity effects on optical properties of quantum well and quantum dot infrared photodetectors

We examined theoretically band structure and discrete dopant effects in the quantum well infrared photodetector (QWIP) and the quantum dot infrared photodetector (QDIP). We find that in QWIPs discrete dopant effects can induce long wavelength infrared absorption through impurity assisted intra-subband optical transitions. In QDIPs, we find that a strategically placed dopant atom in a quantum dot can easily destroy the symmetry and modify the selection rule. This mechanism could be partially responsible for normal incidence absorption observed in low-aspect-ratio quantum dots.     

Donor electron in a quantum well under the influence of an electric field

The ionization energies and the polarizabilities of a donor in an isolated well of a quasi two dimensional (Q2D) GaAs/Ga_1−x Al _x As heterostructure have been obtained for different well widths including electron-lattice coupling. A wave function that properly reduces to the hydrogenic function in the limiting case has been used. For fields of the order of 10⁵ V/m, the ionization energies decrease slightly with electric fields for all well widths (10 nm to 50 nm) studied. Also for a given electric field, as the well width increases, the ionization energy decreases. For fields of the order of 10⁷ V/m and for smaller well widths (<10 nm), the ionization energy generally increases with electric field. The results also show that for electric fields of this order, no donor bound state associated with the lowest subband is possible for well widths greater than 20 nm. The polarizabilities estimated using the expression for the dipole operator show that as the well width increases, the polarizability values also increase and do not show any abnormal behaviour.     

THz laser field effect on the optical properties of cylindrical quantum well wires

The oscillator strength and the linear and third order nonlinear refractive index changes of a cylindrical quantum well wire under intense non-resonant laser field have been investigated within the effective mass-approximation by using a finite element method. We found that the laser amplitude, the incident light and the intersubband relaxation time have an important influence on the refractive index changes.     

Effects of built-in electric field on donor binding energy in InGaN/ZnSnN2 quantum well structures

In_xGa${}_{1?x}$N/ZnSnN₂ quantum well structures are studied in terms of a binding energy of a donor atom. 1s and $2p_{\pm }$ impurity states are considered. The Schrödinger's and Poisson's equations are solved self-consistently. A hydrogenic type wave function to represent each impurity state is assumed. The calculations include band-bending in the potential energy profile introduced by the built-in electric field existing along the structures. The binding energy and the energy of the transition between the impurity states are represented as a function of the quantum well width, the donor position, and the indium concentration. An external magnetic field up to 10 T is included into the calculations to compute the Zeeman splitting. The maximum value of the transition energy is around 30 meV (nearly 7.3 THz) which occurs in a 15-Å In_0.3Ga_0.7N/ZnSnN₂ quantum well. Being strong, the built-in electric field makes the transition energy drop quickly with the decreasing well width. For the same reason, the energy curves are found to be highly asymmetric function of the donor position around the well center. Compared to the bulk value, the transition energy in the quantum well structures enhances nearly two-fold.     

The effect of laser field intensity on polarizability in a quantum well

A systematic study of binding energy of the ground state of a hydrogenic donor in a quantum well is calculated in the presence of a uniform electric field for different measure of laser intensities. Binding energy of the ground state of a donor is calculated, within the effective mass approximation, with the Bessel and Airy functions. Polarizability of a laser dressed donor impurity in the presence of electric field is reported. It is observed that the polarizability (i) increases as intensity of the laser field increases (ii) increases with the electric field strength and (iii) increases drastically when both the fields are applied. The dependence of the donor binding energy on the well width, the laser field intensity and the electric field is discussed. Our results are in good agreement with the previous investigations for other heterostructures in the presence of laser intensity.     

Intense laser effects on nonlinear optical absorption and optical rectification in single quantum wells under applied electric and magnetic field

In this work the effects of intense laser on the electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga_1−xAl_xAs quantum wells are studied under, applied electric and magnetic field. The electric field is applied along the growth direction of the quantum well whereas the magnetic field has been considered to be in-plane. The calculations were performed within the density matrix formalism with the use of the effective mass and parabolic band approximations. The intense laser effects are included through the Floquet method, by modifying the confining potential associated to the heterostructure. Results are presented for the nonlinear optical absorption, the nonlinear optical rectification and the resonant peak of these two optical processes. Several configurations of the dimensions of the quantum well, the applied electric and magnetic fields, and the incident intense laser radiation have been considered. The outcome of the calculation suggests that the nonlinear optical absorption and optical rectification are non-monotonic functions of the dimensions of the heterostructure and of the external perturbations considered in this work.     

Anisotropic optical absorption in quantum well wires induced by high-frequency laser fields

The subband structure and optical properties of a cylindrical quantum well wire under intense non-resonant laser field are investigated by taking into account the correct dressing effect for the confinement potential. The energy levels and wave functions are calculated within the effective mass- approximation using a finite element method. It is found that the absorption coefficient and the saturation intensity are strongly affected by the laser amplitude and frequency as well as by the incident light polarization. As a key result, a large anisotropy in the linear and nonlinear optical absorptions for very intense laser field is predicted. These effects can be useful for the design of polarization sensitive devices.