纤锌矿氮化物量子阱中光学声子模的三元混晶效应

本文先比较了几种常用方法(修正的无规元素等位移模型、虚晶近似和简化相干势近似等)对纤锌矿三元混晶体声子频率的拟合结果,再选用与实验数据接近的拟合方法,结合介电连续和单轴晶体模型导出含纤锌矿三元混晶In_xGa_1－xN和Al_xGa_1－xN单量子阱各类光学声子模的色散关系,进一步分析了声子模随组分的变化. 结果表明,修正的无规元素等位移模型对单模性纤锌矿     

缓冲层对量子阱二能级系统中电子子带间跃迁光吸收的影响

由于ZnO缓冲层对纤锌矿ZnO/Mg_xZn_(1-x)O有限深单量子阱结构左垒的限制作用,导致阱和右垒的尺寸、Mg组分值等因素将影响系统中形成二能级.本文考虑内建电场、导带弯曲及材料掺杂对实际异质结势的影响,利用有限差分法数值求解Schr?dinger方程,获得电子的本征能级和波函数,探讨ZnO缓冲层对此类量子阱形成二能级系统的尺寸效应及三元混晶效应的影响;利用费米黄金法则探讨缓冲层、左垒、阱及右垒宽度和三元混晶效应对此类量子阱电子子带间跃迁光吸收的影响.计算结果显示:对于加入ZnO缓冲层的ZnO/Mg_xZn_(1-x)O有限深单量子阱二能级系统,左垒宽度临界值会随着阱宽和Mg组分值的增大而逐渐减小,随着右垒宽度和缓冲层厚度的增大而逐渐增大;量子阱中电子子带间跃迁光吸收峰会随着左垒、右垒尺寸以及Mg组分的增大发生蓝移,随着阱宽增大而发生红移.本文所得结果可为改善异质结器件的光电性能提供理论指导.     

应变纤锌矿ZnO/Mg_xZn_(1-x)O柱形量子点中离子受主束缚激子的光学性质

在有效质量近似下,考虑内建电场效应,采用变分法详细研究了受限于纤锌矿Mg_xZn_(1-x)O/ZnO/Mg_xZn_(1-x)O圆柱形应变量子点中离子受主束缚激子(A~-,X)的带间光跃迁吸收系数随量子点尺寸、Mg含量和离子受主杂质中心位置的变化情况,并和离子施主束缚激子(D~+,X)及自由激子进行了比较.结果表明:随着量子点尺寸的减小,(A~-,X)的光跃迁吸收强度增强,吸收曲线向高能方向移动,出现蓝移现象.随着Mg含量增加,(A~-,X)的光跃迁吸收曲线蓝移,且吸收强度减弱.随着离子受主杂质从量子点的左界面沿材料生长方向移至量子点的右界面,光跃迁吸收曲线向低能方向移动,出现红移现象.此外,与离子施主束缚激子(D~+,X)相比,随着沿材料生长方向掺入杂质位置的变化,光跃迁吸收曲线移动的方向相反.但不管是掺入离子受主杂质还是离子施主杂质,当离子杂质从量子点的左异质界面沿材料生长方向移至右异质界面时,光跃迁吸收峰的移动量大致相同.     

AlxGa1-xN/GaN双量子阱的结构和掺杂浓度对子带间跃迁波长和吸收系数的影响

用薛定谔方程和泊松方程自洽计算的方法研究了Al_0.75Ga_0.25N/GaN对称双量子阱(DQWs)中子带间跃迁(ISBT)的波长和吸收系数对中间耦合势垒高度、中间耦合势垒宽度、势阱宽度和势垒掺杂浓度的依赖关系.研究发现,第一奇序子带S_1ood与第二偶序子带S_2even ISBT波长随着中间耦合势垒高度的降低而变短.当中间耦合势垒高度高于0.62 eV时,S_{1odd< 关键词： 自洽 x}Ga_1-xN/GaN双量子阱')" href="#">Al_xGa_1-xN/GaN双量子阱 子带间跃迁     

1.55μmSi_(1-x)Ge_x光波导与Si_(1-x)Ge_x/Si多量子阱探测器集成的优化设计

对１．５５μｍ波长的Ｓｉ１－ｘＧｅｘ光波导和Ｓｉ１－ｘＧｅｘ／Ｓｉ多量子阱（ＭＱＷ）红外探测器的集成器件结构进行了系统的分析和优化设计。优化结果为：１）对Ｓｉ１－ｘＧｅｘ光波导，Ｇｅ含量ｘ＝０．０５，脊宽、高和腐蚀深度分别为８、３和２．６μｍ；２）对Ｓｉ１－ｘＧｅｘ／Ｓｉ多量子阱红外探测器，Ｇｅ含量ｘ＝０．５，探测器由厚度为５５０ｎｍ、２３个周期的６ｎｍＳｉ０．５Ｇｅ０．５＋１７ｎｍＳｉ组成，长度约２ｍｍ。结果表明，这种结构器件的内量子效率可达８８％。     

AlxGa1-xN/GaN双量子阱的结构和掺杂浓度对子带间跃迁波长和吸收系数的影响

用薛定谔方程和泊松方程自洽计算的方法研究了Al0.75Ga025N/GaN对称双量子阱(DQWs)中子带间跃迁(ISBT)的波长和吸收系数对中间耦合势垒高度、中间耦合势垒宽度、势阱宽度和势垒掺杂浓度的依赖关系.研究发现,第一奇序子带S1ood与第二偶序子带S2evenISBT波长随着中间耦合势垒高度的降低而变短.当中间耦合势垒高度高于0.62 eV时,Slotld-S:一ISBT吸收系数随着中间耦合势垒的降低而增加.当减小AlxGa1-xN/GaN的DQWs中间耦合势垒宽度时,S1odd-S2evenISBT波长将变短,其吸收系数变大.另一方面,当对称DQWs的势阱宽度大于1.9 nm时,S1odd-S2evenISBT波长随着势阱的变窄而减小,S1odd-S2evenISBT吸收系数随着势阱的变窄而增加.当势垒中的掺杂浓度小于1018/cm3时,S1odd-S2evenISBT波长基本不随掺杂浓度变化,而吸收系数随掺杂浓度的增加而增加.这些结果对于利用DQWs实现工作于光纤通信波段超快的、基于三能级或四能级系统的双色光电子器件的应用具有指导意义.     

应变纤锌矿ZnO/Mg_xZn_(1-x)O盘形量子点中的离子施主束缚激子态（英文）

在有效质量近似下,计算了盘形量子点中离子施主束缚激子的结合能、光跃迁能、振子强度及辐射寿命.设盘形量子点由有限长的柱形ZnO材料组成,四周被MgxZn1-xO包围,离子施主局域在盘轴.考虑了由于自发极化和压电极化引起的内建电场效应,并在有限深约束势下采用合适的变分波函数进行.计算结果表明,量子盘结构参数(盘高度及垒中Mg组分)和离子施主的位置对离子施主束缚激子的结合能、光跃迁能、振子强度及辐射寿命有强烈的影响.随着盘高度的增加,结合能、光跃迁能和振子强度减小,而辐射寿命增加.对含Mg量较高的盘形量子点,盘高度对结合能、光跃迁能、振子强度及辐射寿命的影响更显著.当施主杂质位于量子点的左界面附近时结合能(光跃迁能)有极大(极小)值,而当施主杂质位于量子点的右界面附近时结合能(光跃迁能)有极小(极大)值.     

蓝光激光器结构中InGaN/GaN多量子阱界面效应的精细光致发光光谱研究

金属有机化学气相沉积(MOCVD)方法制备InGaN/GaN多量子阱结构时,在GaN势垒层生长的N2载气中引入适量H2,能够有效改善阱/垒界面质量从而提升发光效率.本工作利用光致发光(PL)光谱技术,对蓝光激光器结构中的InGaN/GaN多量子阱的发光性能进行了精细的光谱学测量与表征,研究了通H2生长对量子阱界面的调控...     

纤锌矿In_(0.19)Ga_(0.81)N/GaN量子阱中光学声子和内建电场对束缚极化子结合能的影响

用改进的Lee-Low-Pines变分方法研究纤锌矿In0.19Ga0.81N/GaN量子阱结构中束缚极化子能量和结合能等问题,给出基态结合能、不同支长波光学声子对能量和结合能的贡献随阱宽和杂质中心位置变化的数值结果.在数值计算中包括了该体系中声子频率的各向异性和内建电场对能量和结合能的影响、以及电子和杂质中心与长波光学声子的相互作用.研究结果表明,In0.19Ga0.81N/GaN量子阱材料中光学声子和内建电场对束缚极化子能量和结合能的贡献很大,它们都引起能量和结合能降低.结合能随着阱宽的增大而单调减小,窄阱中减小的速度快,而宽阱中减小的速度慢.不同支声子对能量和结合能的贡献随着阱宽的变化规律不同.没有内建电场时,窄阱中,定域声子贡献小于界面和半空间声子贡献,而宽阱中,定域声子贡献大于界面和半空间声子贡献.有内建电场时,定域声子贡献变小,而界面和半空间声子贡献变大,声子总贡献也有明显变化.在In0.19Ga0.81N/GaN量子阱中,光学声子对束缚极化子能量和结合能的贡献比GaAs/Al0.19Ga0.81As量子阱中的相应贡献(约3.2—1.8和1.6—0.3 meV)约大一个数量级.阱宽(d=8 nm)不变时,在In0.19Ga0.81N/GaN量子阱中结合能随着杂质中心位置Z0的变大而减小,并减小的速度变快.随着Z0的增大,界面和半空间光学声子对结合能的贡献缓慢减小,而定域光学声子的贡献缓慢增大.     

(La1-xYx)2/3Ca1/3MnO3(x=0～0.3)体系的磁特性与平均稀土离子尺寸效应的研究

研究了(La1-xYx)2/3Ca1/3MnO3(0.0≤x≤0.3)体系的磁特性,给出了磁转变温度Tc与La位平均离子尺寸之间的关联.结果表明,随Y掺杂浓度的增加,金属-绝缘转变(M-I)温度TMI向低温区移动,对应的峰值电阻率ρp升高,对x=0.3样品而言,较未替代样品(x=0.0)增幅达8个数量级之多,指出由于Y的掺入而致使La位平均离子半径()减少以及局域晶格结构畸变引起的.磁性测量表明了在x>0.1的高浓度区域,随着x的增加,反铁磁性相互作用逐渐增强,导致x=0.2和x=0.3的样品在35K左右出现了自旋玻璃态.     

Phonon-assisted intersubband transitions in wurtzite GaN/InxGa1-xN quantum wells

A detailed numerical calculation on the phonon-assisted intersubband transition rates of electrons in wurtzite GaN/In_xGa_1-xN quantum wells is presented. The quantum-confined Stark effect induced by the built-in electric field and the ternary mixed crystal effect are considered. The electron states are obtained by iteratively solving the coupled Schrödinger and Poisson equations and the dispersion property of each type of phonon modes is considered in the derivation of Fermi's golden rule to evaluate the transition rates. It is indicated that the interface and half-space phonon scattering play an important role in the process of 1-2 radiative transition. The transition rate is also greatly reduced by the built-in electric field. The present work can be helpful for the structural design and simulation of new semiconductor lasers.     

纤锌矿结构Zn1-xMgxO电子结构及吸收光谱的第一性原理研究

采用第一性原理计算方法,计算了纤锌矿结构Zn_1-xMg_xO(x=0,00625,0125,025)的电子结构及吸收光谱. 计算结果表明,Mg的掺入使ZnO的电子结构发生了较大的改变,与Mg邻近的O原子得到电子的数目明显增大,进而O原子返回部分电子给邻近Zn原子. Zn-O间相互作用减弱,禁带宽度变大,这也从同一合金中Zn4s上移的程度得到证实. 其吸收光谱也随着Mg的掺入出现蓝移现象,其吸收边对应波长分别为379, 关键词： 第一性原理计算 电子结构 吸收光谱 纤锌矿结构ZnO     

Optical properties of exciton confinement in wurtzite ZnO/MgxZn1−xO coupled quantum dots

Based on the framework of effective-mass approximation and variational approach, optical properties of exciton are investigated theoretically in ZnO/Mg_xZn_1−xO vertically coupled quantum dots (QDs), with considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects due to the piezoelectricity and spontaneous polarization. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the different structural parameters (the dot height and the barrier thickness between the coupled wurtzite ZnO QDs) are calculated with the built-in electric field in detail. The results elucidate that structural parameters have a significant influence on the exciton state and optical properties of ZnO coupled QDs. These results show the optical and electronic properties of the quantum dot that can be controlled and also tuned through the nanoparticle size variation.     

Spatially nonlocal effects on optical absorption properties in coupled quantum wells with an applied electric field

Based on the microscopic nonlocal optical response theory, the intersubband optical absorption properties in AlGa As/Ga As couple quantum wells（CQWs） are investigated for p-polarized states. The numerical results show that spatial nonlocality of optical responses can induce a radiation shift on optical absorption spectra due to nonlocal effects. The dependence of the radiation shift on the CQW structure and the applied electric field is clarified. It is also demonstrated that the maximal radiation shift and the least optical absorbance can be obtained by adopting an appropriate CQW structure and a suitable applied electric field. This work may provide some methods of designing the nanomaterials with controllable nonlocality and observing the spatial nonlocal effects in experiment.     

Magnesium incorporation efficiencies in Mg_xZn_(1-x)O films on ZnO substrates grown by metalorganic chemical vapor deposition

We investigate the magnesium(Mg) incorporation efficiencies in Mg_xZn_(1-x)O films on c-plane Zn-face ZnO substrates by using metalorganic chemical vapor deposition(MOCVD) technique. In order to deposit high quality Mg_xZn_(1-x)O films,atomically smooth epi-ready surfaces of the hydrothermal grown ZnO substrates are achieved by thermal annealing in O_2 atmosphere and characterized by atomic force microscope(AFM). The AFM, scanning electron microscope(SEM),and x-ray diffraction(XRD) studies demonstrate that the Mg_xZn_(1-x)O films each have flat surface and hexagonal wurtzite structure without phase segregation at up to Mg content of 34.4%. The effects of the growth parameters including substrate temperature, reactor pressure and Ⅵ/Ⅱ ratio on Mg content in the films are investigated by XRD analysis based on Vegard's law, and confirmed by photo-luminescence spectra and x-ray photoelectron spectroscopy as well. It is indicated that high substrate temperature, low reactor pressure, and high Ⅵ/Ⅱratio are good for obtaining high Mg content.     

Influence of Mg content on optical properties of exciton confinement in wurtzite ZnO/MgxZn1−xO coupled quantum dots

Based on the framework of effective-mass approximation and variational approach, optical properties of exciton are investigated theoretically in ZnO/Mg_xZn_1−xO vertically coupled quantum dots (QDs), with considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the structural parameters (the dot height, the barrier thickness between the coupled wurtzite ZnO QDs and Mg content x in the barrier layers) is calculated in detail. The results elucidate that Mg content have a significant influence on the exciton state and optical properties of ZnO coupled QDs. When Mg content x increases, the strong built-in electric field increases and leads to the redshift of the effective band gap of the Mg_xZn_1−xO layer. These theoretical results are useful for design and application of some important photoelectronic devices constructed by using ZnO strained QDs.     

Built-in electric field effect on cyclotron mass of magnetopolarons in a wurtzite In_xGa_（1-x）N/GaN quantum well

The cyclotron mass of magnetopolarons in wurtzite In x Ga 1 x N/GaN quantum well is studied in the presence of an external magnetic field by using the Larsen perturbation method.The effects of the built-in electric field and different phonon modes including interface,confined and half-space phonon modes are considered in our calculation.The results for a zinc-blende quantum well are also given for comparison.It is found that the main contribution to the transition energy comes from half-space and interface phonon modes when the well width is very small while the confined modes play a more important role in a wider well due to the location of the electron wave function.As the well width increases,the cyclotron mass of magnetopolarons first increases to a maximum and then decreases either with or without the built-in electric field in the wurtzite structure and the built-in electric field slightly reduces the cyclotron mass.The variation of cyclotron mass in a zinc-blende structure is similar to that in a wurtzite structure.With the increase of external magnetic field,the cyclotron mass of polarons almost linearly increases.The cyclotron frequency of magnetopolarons is also discussed.     

Be-composition effect on structure, electronic and optical properties of BexZn1-xO alloys

This paper carries out first principles calculation of the structure,electronic and optical properties of Be x Zn 1 x O alloys based on the density-functional theory for the compositions x = 0.0,0.25,0.5,0.75,1.0.The lattice constants deviations of alloys obey Vegard’s law well.The Be x Zn 1 x O alloys have the direct band gap(Γ-Γ) character,and the bowing coefficients are less than the available theoretical values.Moreover,it investigates in detail the optical properties(dielectric functions,absorption spectrum and refractive index) of these ternary mixed crystals.The obtained results agree well with the available theoretical and experimental values.