GaN／GaAIN宽量子阱的二类激光特征

考虑了内建电场的影响，用变分法计算了GaN/GaAIN量子阱（QW）的电子子带和激子结合能。结果表明，对于阱宽较大情形，电子和空穴高度局域在QW边沿附近。内建电场造成的电子空穴空间的较大分离使QW激子表现出二类阱特征，重空穴基态结合能对Al浓度变化不敏感。     

流体静压力下应变闪锌矿(111)取向GaN/AlGaN量子阱中受屏蔽激子的结合能

结合变分法与自洽计算方法研究了流体静压力下应变闪锌矿(111)取向GaN/AlχGa1-χN量子阱中受电子-空穴气体屏蔽的激子结合能.计算中,考虑了沿(111)取向生长多层结构时存在压电极化引起的内建电场.计算结果表明,考虑压力对双轴及单轴应变的调制以及禁带宽度、有效质量和介电常数等参数的压力效应时,激子结合能随压力的增大近似线性增加;且当电子-空穴气体密度大时,这一效应更加显著.当给定压力时,随着电子.空穴气面密度的增加,激子结合能先缓慢增加,但当密度达到大约1011cm-2时结合能开始迅速衰减.此外,当减小垒的厚度时,由于内建电场减弱,激子结合能显著增加.     

流体静压力下应变闪锌矿(111)取向GaN/AlGaN量子阱中受屏蔽激子的结合能

结合变分法与自洽计算方法研究了流体静压力下应变闪锌矿(111)取向GaN/AlχGa1-χN量子阱中受电子-空穴气体屏蔽的激子结合能.计算中,考虑了沿(111)取向生长多层结构时存在压电极化引起的内建电场.计算结果表明,考虑压力对双轴及单轴应变的调制以及禁带宽度、有效质量和介电常数等参数的压力效应时,激子结合能随压力的增大近似线性增加;且当电子-空穴气体密度大时,这一效应更加显著.当给定压力时,随着电子.空穴气面密度的增加,激子结合能先缓慢增加,但当密度达到大约1011cm-2时结合能开始迅速衰减.此外,当减小垒的厚度时,由于内建电场减弱,激子结合能显著增加.     

耦合ZnO/MgxZn1-xO量子点中的激子态和带间光跃迁

在有效质量近似和变分原理的基础上,考虑量子点的三维约束效应和内建电场.研究了ZnO/MgxZn1-xO0耦合量子点中激子结合能、带间光跃迁能以及电子-空穴复合率随量子点结构参数(量子点高度和势垒层厚度)的变化.结果表明:激子结合能、带间光跃迁能和电子-空穴复合率随量子点高度或势垒层厚度的增加而降低.     

势阱形状对电场下量子阱子带和激子能移的影响

在束缚态近似下,用级数解法求解电场下各种不同形状GaAs/GaAlAs量子阱中电子和空穴子带,进一步采用变分方法得到激子结合能.由此,我们首次得到电场下由抛物阱至方位阱子带和激子峰能移的变化图象.在考虑GaAs/GaAlAs量子阱形状影响的基础上,我们计算所得结果与实验吻合得很好.     

GaN基量子阱激子结合能和激子光跃迁强度

采用变分法,计算了GaN基量子阱中激子结合能和激子光跃选强度。计算结果表明,GaN基量子阱中激子结合能为10－55meV,大于体材料中激子结合能,并随着阱宽减小而增加,在临界阱宽处达到最大。结间带阶同样对激子结合能有着较大的影响,更大带阶对应更大的结合能。同时量子限制效应增加了电子空穴波函数空间重叠,因此加强了激子光跃迁振子强度,导致GaN/AlN量子阱中激子光吸收明显强于体材料中激子光吸收。     

纤锌矿GaN/AlxGa1-xN量子阱中激子能量

考虑了纤锌矿GaN/Al<,x>Ga<,1-x>N量子阱(QW)材料中空穴带质量和光学声子模的各向异性以及声子频率随波矢变化的效应,采用改进的LLP变分法计算了纤锌矿氮化物QW中激子的基态能量和结合能.给出了激子的基态能量和结合能随着QW宽度和Al组分变化的函数关系,并对闪锌矿和纤锌矿GaN/Al<0.3>Ga<,0....     

Al含量对GaN/Alx Ga1-x N量子点中激子态的影响

利用有效质量方法和变分原理,考虑内建电场和量子点的三维约束效应,研究了Al含量对局域在GaN/AlxGa1xN量子点中激子性质的影响.结果表明,随着Al含量的增加,GaN/AlxGa1-xN异质界面处的导带不连续性增强,势垒变高,载流子受到的约束增强,激子结合能增加,电子-空穴的复合率先增大后减小,且存在最大值.对给定体积的量子点,随其高度的变化激子结合能存在最大值,相应的电子-空穴被最有效约束,激子态最稳定.     

外场对InPBi量子阱中激子结合能的影响

在有效质量近似下运用变分法计算了InAlAs/InPBi/InAlAs量子阱中的激子结合能随阱宽、Al组分、Bi组分的变化情况,分析了外加电场和磁场对激子结合能的影响。结果表明：激子结合能随阱宽增大呈现先增大后减小的趋势;随Al、Bi组分的增大,激子结合能也逐渐增大;外加电场较小时对激子结合能的影响很小,外加电场较大时破坏了激子效应;激子结合能随外加磁场增大呈现单调增大的趋势。计算结果对InAlAs/InPBi/InAlAs量子阱在光电子器件方面的应用有一定指导意义。     

Al含量对GaN/AlxGa1－xN量子点中激子态的影响

利用有效质量方法和变分原理，考虑内建电场和量子点的三维约束效应，研究了Al含量对局域在GaN/AlxGa1－xN量子点中激子性质的影响．结果表明，随着Al含量的增加，GaN/AlxGa1－xN异质界面处的导带不连续性增强，势垒变高，载流子受到的约束增强，激子结合能增加，电子空穴的复合率先增大后减小，且存在最大值．对给定体积的量子点，随其高度的变化激子结合能存在最大值，相应的电子空穴被最有效约束，激子态最稳定．     

Characterization of excitons in wurtzite GaN quantum wells undervalence band mixing, strain, and piezoelectric field

Low-dimensional excitons in general, and quantum-well (QW) excitons in particular, are important for linear and nonlinear semiconductor optics applications. The recent observation of the high binding energy of bulk excitons in gallium nitride samples being the main impetus, we undertake a theoretical work to characterize QW excitons in wurtzite semiconductors. In our formulation, we take into account valence band mixing, strain, and piezoelectric field effects. The in-plane behavior of excitons is treated variationally, whereas the finite-element method is used for the dependence along the growth direction. The formulation is applied to GaN-Al_x Ga_1-x N QW's. The presence of the piezoelectric field leads to the well-known quantum-confined Stark effect. We deduce from an oscillator strength analysis that the quantum-confined Franz-Keldysh effect is operational for QW's of width around 45 Å for an aluminum content of x=0.15. Our results further indicate that, for very clean samples, QW excitons should not ionize at room temperature even in the presence of the piezoelectric field for sufficiently narrow QW's. We determine the fractional dimensionality of the QW excitons in the absence of the piezoelectric field, which can in principle be cancelled by introducing delta-doped ionized layers on either side of the QW. The absorption spectra associated with the low-lying 1s excitons are also presented for several well widths     

GaAlN/GaN量子阱中电子的激发态极化及其压力效应

考虑了纤锌矿结构材料的各向异性造成的内建电场的作用以及各向异性造成的应变张量和静压形变势与各向同性材料的差别.在此基础上计算了GaN/GaAIN量子阱内电子的激发态极化.研究了压力(应变)对电子激发态极化的影响.结果表明,电子势垒高度、电子有效质量和电子激发态极化均随压力线性下降,但由于内建电场的作用造成电子波函数高度局域化,上述变化的幅度不大.     

缀饰激子在半导体微腔中的辐射

本文建立了半导体微腔的缀饰激子模型,在ＶＣＳＥＬ器件量子阱中的激子首先通过内电磁场与腔耦合,形成缀饰态。而后作为多粒子过程,缀饰激子与腔内真空场耦合产生辐射。通过ＱＥＤ方法,我们得到偶极子辐射密度方程和系统能量衰 变方程。从方程解的讨论中,我们得到超辐射和偶极子微腔方向 效应的结果,同时预言民当内场耦合足够强时,缀 激子可以直接辐射到一个很的激光模中。     

Design of double and triple quantum wells for InGaAs-AlAsSbintersubband unipolar semiconductor lasers

InGaAs-AlAsSb double and triple quantum well (QW) structures were designed in an effort to shorten the wavelength to less than 2 μm for possible application to intersubband unipolar lasers. Wavelengths corresponding to the intersubband separation, the minimum and maximum operating electric field, optical-phonon-limited nonradiative scattering time, and escape time from the QW were simulated. It was found that suitable nonradiative transition times can be obtained by properly designing the coupling layer thickness for both kinds of QW's. The minimum wavelength is 1.5 μm and an operating electric field is above 130 kV/cm for wavelengths <2 μm in the double QW. On the other hand, the minimum operating electric field is less than 10 kV/cm and the minimum wavelength is about 1.7 μm for the triple QW. The triple QW is suitable for an electric-field induced wavelength tunable laser     

方形半导体量子线中光吸收的横向斯塔克效应

The ground and few excited states of the electrons confined in a square GaAs quantum wire(QW) subjected to an external transverse electric field are investigated using the finite difference method within the effective-mass approximation. When the transverse electric field is applied along a side of the square quantum wire, the calculation of the eigenstates of the quantum wire has an exactly solvable problem whose solutions involve the linear combinations of two independent Airy functions. Compared with the exact analytical results using Airy functions, the results obtained by the use of the finite difference method in terms of the eigenstates of the particle in the QW are in excellent agreement. Subsequently, it is considered that the eigenstates of the particle depend on the orientations of the electric field with respect to the center axis of the QW. It is interesting that the peak value of the energy is found for the field directed along the diagonal in the QW, which can lead to a large energy shift. Meanwhile, dependence of the optical absorption phenomenon in the square QW on the optical field and applied electric field is investigated. It is shown that the optical absorption spectrum depends highly upon the polarization of the optical field and the applied electric field intensities and orientations.     

Electric-field-induced exciton transport in coupled quantum well structures

We report on a conceptionally new approach to achieve electrostatically induced in plane exciton transport in quantum well (QW) structures. Experimentally, exciton transport is demonstrated in an electric-field-tunable GaAs/AlAs coupled quantum well structure, in a regime, where electrons and holes are separated in real space. In spatially resolved photoluminescence experiments it is shown that, the excitons experience a drift field, which is given by an electric-field-induced, in plane band gap gradient.     

InGaN/GaN quantum well growth on pyramids of epitaxial lateral overgrown GaN

InGaN/GaN quantum wells (QW) were grown by metalorganic chemical vapor deposition (MOCVD) on pyramids of epitaxial lateral overgrown (ELO) GaN samples. The ELO GaN samples were grown by MOCVD on sapphire (0001) substrates that were patterned with a SiN_x mask. Scanning electron microscopy and cathodoluminescence (CL) imaging experiments were performed to examine lateral variations in structure and QW luminescence energy. CL wavelength imaging (CLWI) measurements show that the QW peaks on the top of the grooves are red-shifted in comparison with the QW emission from the side walls. The results show that In atoms have migrated to the top of the pyramids during the QW growth. The effects of V/III ratio, growth temperature as well as ELO GaN stripe orientation on the QW properties are also studied.     

Effects of electric field on the exciton linewidth broadening dueto scattering by free carriers in semiconducting quantum-well structures

The effects of an applied electric field perpendicular to the well layers on the broadening of the exciton linewidth due to scattering by free carriers in semiconducting quantum well (QW) structures is theoretically investigated based on a finite confining potential model. The dependence of the free carrier-exciton linewidth broadening on carrier concentration, temperature, and well width are calculated and discussed for various electric field strengths. It is found that the influence of the electric field on the linewidth broadening is appreciable in wide wells, while in narrow wells little change is shown even in the presence of a strong electric field     

CuPc/C60 heterojunction thin film optoelectronic devices

The optoelectronic properties of heterojunction thin film devices with ITO/CuPc/C60/A1 structure have been investigated by analyzing their current-voltage characteristics,optical absorption and photocurrent.In this organic photovoltaic device,CuPc acts as an optically active layer,C60 as an electron-transporting layer and ITO and A1 as electrodes.It is observed that,under illumination,excitons are formed,which subsequently drift towards the interface with C60,where an internal electric field is present.The excitons that reach the interface are subsequently dissociated into free charge carriers due to the electric field present at the interface.The experimental results show that in this device the total current density is a function of injected carriers at the electrode-organic semiconductor surface,the leakage current through the organic layer and collected photogenerated current that results from the effective dissociation of excitons.     

Radiative recombination in Zn1-x MnxTe/Zn0.59Mg0.41Te quantum well structures: Exciton emission and intracenter luminescence

The luminescence spectra controlled by excitons and intracenter 3d emission of Mn²⁺ ions are studied for a series of Zn_1-x Mn_xTe/Zn_0.59Mg_0.41 Te quantum well (QW) structures that differ in manganese content and QW width. It is shown that the relative intensities of exciton emission of the QWs and barriers and the dependences of the intensities on the optical excitation level are controlled mainly by the manganese content in the QWs that affect the efficiency of excitons transfer of to the 3d shell of the Mn²⁺ ions. The effects of QW width and manganese content on the decay kinetics of the intracenter luminescence of the Mn²⁺ ions are studied.