纤锌矿AlGaN/AlN/GaN异质结构中光学声子散射影响的电子迁移率

对含有AlN插入层纤锌矿Al_xGa_1-xN/AlN/GaN异质结构,考虑有限厚势垒和导带弯曲的实际 异质结势,同时计入自发极化和压电极化效应产生的内建电场作用,采用数值自洽求解薛定谔方程和泊松方程, 获得二维电子气(2DEG)中电子的本征态和本征能级.依据介电连续模型和Loudon单轴晶体模型, 用转移矩阵法分析该体系中可能存在的光学声子模及三元混晶效应.进一步, 在室温下计及各种可能存在的光学声子散射,推广雷-丁平衡方程方法,讨论2DEG分布及二维电子迁移率的 尺寸效应和三元混晶效应.结果显示: AlN插入层厚度和Al_xGa_1-xN势垒层中Al组分的增加均会 增强GaN层中的内建电场强度,致使2DEG的分布更靠近异质结界面,使界面光学声子强于其他类型的 光学声子对电子的散射作用而成为影响电子迁移率的主导因素.适当调整AlN插入层的厚度和Al组分, 可获得较高的电子迁移率.     

室温下Ga1-xHoxN (x=0.0 and 0.05)稀磁半导体薄膜磁性

采用热蒸镀技术和后续氨退火制备了Ho掺杂GaN稀磁半导体薄膜. X射线衍射分析表明,所有的峰属于六角纤锌矿结构. 利用扫描电子显微镜和能量色散谱分别进行了表面形貌和成分分析. 用振动样品磁强计在室温测定了Ga_1-xHo_xN(x=0.0,0.05)的室温铁磁性. 磁性测量结果表明,未掺杂薄膜GaN具有抗磁性行为,而Ho掺杂Ga_0.95Ho_0.05N的薄膜表现出铁磁行为.     

共轭低聚物中光生分子间电荷转移态的第一性原理研究

本文基于第一性原理中的Heyd-Scuseria-Ernzerh方法研究了单层In_1-xGa_xN的电子结构和光学性质.计算得到单层In_1-xGa_xN的能带结构和态密度（DOS）,发现随着掺杂比例的变化,体系带隙的变化范围是1.8~3.8 eV,表明通过Ga的掺杂可以实现体系带隙值的调节.并且还研究了单层In_1-xGa_xN的介电函数,折射率和吸收系数等光学性质,结果表明随着Ga掺杂浓度的增加,介电函数谱的主峰和吸收谱发生了显著的蓝移.此外,基于能带结构和态密度图谱,对单层In_1-xGa_xN的光学性质进行分析,预测这种材料独特的光学性质在纳米电子学和光学器件中会有广泛的应用.     

纤锌矿BeO掺Cd的电子结构与能带特性研究

采用基于密度泛函理论平面波赝势方法, 对纤锌矿BeO掺Cd的Be_1-xCd_xO合金进行电子结构与能带特性研究. 结果表明: Be_1-xCd_xO的价带顶始终由O 2p电子态决定, 而导带底由Be 2s和Cd 5s的电子态决定.随着Be_1-xCd_xO合金的Cd掺杂量增加, Cd 4d与O 2p的排斥效应逐渐加强, 同时Be_1-xCd_xO的带隙逐渐变小, 出现"直接-间接-直接"的带隙转变. 为了使理论值与实验值相一致, 对Be_1-xCd_xO带隙进行修正, 并分析了纤锌矿BeO-ZnO-CdO三元合金的带隙和弯曲系数与晶格常数的关系.     

非对称方势阱中的激子及其与声子的相互作用

采用类LLP(Lee-Low-Pines)变换和分数维变分法,在讨论有限深非对称方势阱Ga_1－xAl_xAs/ GaAs/Ga_0.7Al_0.3As的分数维基础上,计算了其中激子的基态能量以及声子对其影响,随着势阱宽度增加,激子能量先减小后增大,出现一个最小值.讨论了一侧势垒高度变化对分数维、激子基态能量的影响,并发现声子作用使得激子能量明显增大.另外,非对称方势阱中的激子结合能随阱宽的减小而增     

MOCVD制备InxGa1－xN/GaN MQWs的温度依赖性

利用方势阱模型对In_xGa_1－xN/GaN MQWs结构的光特性进行了量子力学定性理论分析.并在MO源流量恒定条件下，在570℃～640℃范围内进行了不同生长温度的多量子阱制备实验，对In_xGa_1－xN制备过程中的In组份掺入效率的温度依赖关系进行研究.通过对制备样品的PL谱测量分析，得到了587℃～600℃的In组份最佳掺入温度区间.     

纤锌矿GaN/ZnO 量子阱中的界面声子及其电声相互作用

根据介电连续模型和单轴晶体模型研究了纤锌矿量子阱中的界面声子模及其电声子相互作用的Fröhlich哈密顿。我们计算和讨论了纤锌矿GaN/ZnO单量子阱中的界面声子的色散关系和电声相互作用的耦合强度。色散曲线充分体现了纤锌矿晶体的各向异性;四支界面声子模出现在两个能量区域中,分别是：[ , ]和[ , ]。界面声子模出现消失的现象,光学声子模之间存在能量交迭区域。我们的结果也阐述了纤锌矿GaN/ZnO单量子阱中每支声子模与电子相互作用的对称性和耦合强度。     

InxGa1－xAs缓冲层上InyGa1－yAs/(Al)Ga

本文中,发现在In_xGa_1-xAs缓冲层上非故意掺杂的In_yGa_1-yAs/(Al)GaAs超晶格样品中存在着两个互相反向的自建电场区,一个位于样品表面,另一个位于In_xGa_1-xAs缓冲层和超晶格界面。据此,合理地解释了样品的光伏测试结果,并对此类样品的MOCVD生长工艺给予指导。     

Ⅰ类和Ⅱ类准周期半导体超晶格的电子子带和波函数

本文将包迹函数近似推广用于计算有理数近似下,垂直于超晶格轴的波矢K_⊥不等于零时,准周期半导体超晶格(QSS)的电子子带和波函数,对K_⊥=0的情形,分别计算了Ⅰ类的GaAs/Al_xGa_1-xAs和Ⅱ类的InAs/GaSb QSS的电子子带和波函数,直至代序数m=9和6。对于价带对导带影响强的InAs/GaSb QSS,分别计算了m=5和6时电子子带随K_⊥的变化关系。并提出了利用本文结果计算Ⅰ类的GaAs/Al_xGa_1-xAs QSS带间集体激发的具体方法。     

Zn掺杂n型笼合物Ba8Ga16-2xZnxGe30+x的热电传输特性

用高温熔融结合放电等离子烧结法制备了Zn掺杂单相n型Ba₈Ga_16-2xZn_xGe_30+x笼合物，探索了Zn对Ga的取代对其热电传输特性的影响规律.研究结果表明,n型Ba₈Ga_16-2xZn_xGe_30+x化合物的电导率随着x的增加逐渐增     

Dispersions of quasi-confined optical phonon modes and their electron–phonon interactions in an asymmetric wurtzite AlxGa1−xN / GaN / Aly Ga1−yN quantum well

Within the framework of the dielectric continuum model and Loudon’s uniaxial crystal model, the properties of the quasi-confined (QC) optical phonon dispersions and the electron–QC phonons coupling functions in an asymmetric wurtzite quantum well (QW) are deduced via the method of electrostatic potential expanding. The present theoretical scheme can be treated as a generalization of the QC optical phonons in an ordinary wurtzite double heterostructures QWs, and it can be reduced naturally to the situation of the symmetrical wurtzite QW once a suite of symmetrical parameters are adopted. Numerical computation on an asymmetric AlN/ GaN/ Al_0.15Ga_0.85N wurtzite QW are performed, and a detailed comparison with the case in symmetric wurtzite QW is carried out. The calculated results show that the structural asymmetry of wurtzite QW changes greatly the dispersion behaviors and the electrostatic potential distributions of the QC optical phonon modes.     

Optical phonon modes in graded III-V nitride quantum wells

The dispersion relation for optical phonon modes in graded wurtzite AlN/GaN and AlN/InN quantum wells is calculated taking into account the existence of interfacial transition regions. We make use of a model based on the macroscopic theory developed by Loudon, known as the continuum dielectric model. The optical phonon modes are modelled considering only the electrostatic boundary conditions (neglecting retardation effects), in the absence of charge transfer between ions. We show that the graded interfaces strongly shift the frequencies of the phonon modes of the otherwise abrupt nitrides quantum wells.     

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.     

Surface phonon–polaritons in rectangular quantum wires of polar ternary mixed crystals

In this paper, the dispersion relations of surface phonon–polaritons in freestanding rectangular quantum wire systems of polar ternary mixed crystals are derived. The numerical calculations for Al_xGa_1−xAs and Zn_xCd_1−xSe quantum wire systems are performed. The results reveal that the frequencies of surface phonon–polariton modes are sensitive to the geometric structures of the quantum wires, the wave-vectors in z-direction, and the compositions of the ternary mixed crystal materials. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface phonon–polariton modes are also discussed.     

Ternary mixed crystal effects on interface optical phonon and electron-phonon coupling in zinc-blende GaN/AlxGa1−xN spherical quantum dots

The theoretical investigations of the interface optical phonons, electron–phonon couplings and its ternary mixed effects in zinc-blende spherical quantum dots are obtained by using the dielectric continuum model and modified random-element isodisplacement model. The features of dispersion curves, electron–phonon coupling strengths, and its ternary mixed effects for interface optical phonons in a single zinc-blende GaN/Al_xGa_1−xN spherical quantum dot are calculated and discussed in detail. The numerical results show that there are three branches of interface optical phonons. One branch exists in low frequency region; another two branches exist in high frequency region. The interface optical phonons with small quantum number l have more important contributions to the electron–phonon interactions. It is also found that ternary mixed effects have important influences on the interface optical phonon properties in a single zinc-blende GaN/Al_xGa_1−xN quantum dot. With the increase of Al component, the interface optical phonon frequencies appear linear changes, and the electron–phonon coupling strengths appear non-linear changes in high frequency region. But in low frequency region, the frequencies appear non-linear changes, and the electron–phonon coupling strengths appear linear changes.     

Polar oscillation and dispersion properties of quasi-confined optical phonon modes in a wurtzite GaN/AlxGa1−xN nanowire

Under the dielectric continuum model and Loudon’s uniaxial crystal model, the properties of the quasi-confined (QC) optical phonon dispersions and the electron-QC phonons coupling functions in a cylindrical wurtzite nanowire are deduced via the method of electrostatic potential expanding. Numerical computations on a GaN/Al_0.15Ga_0.85N wurtzite nanowire are performed. Results reveal that, for a definite axial wave number k_z and a certain azimuthal quantum number m, there are infinite branches of QC modes. The frequencies of these QC modes fall into two regions, i.e. a high frequency region and a low frequency region. The dispersion of the QC modes are quite apparant only when k_z and m are small. The lower-order QC modes in the higher frequency region play more important role in the electron-QC phonon interactions. Moreover, for the higher-order QC modes in the high frequency region, the electrostatic potentials “escaping” out of the well-layer material nearly could be ignored.     

The Investigation of Plasmon-Longitudinal Optical Phonon Coupling and Surface Polariton Modes in Donor Doped GaAs-Al0.33Ga0.67As Multi Quantum Wells

Infrared Fourier transform spectroscopy has been used to investigate phonon, plasmon, surface polariton and plasma-longitudinal optical phonon coupling in highly donor doped multi quantum wells (GaAs/Al_0.33Ga_0.67As) and direct band gap n- type Al_XGa_1-XAs thin layer on GaAs substrate. Using different samples with different concentration of free carriers. The dispersion equation of coupling modes have been calculated by using the condition which the dielectric functions of samples are zero for longitudinal coupled modes and experimental papameters which have been obtained from the best fit p-polarized oblique incidence far infrared reflection spectra. In MQW samples, the free carriers confined to the well and carriers are quasi two dimensional. So, plasmon- LO phonon coupling occur in the well (GaAs). In n- type Al_XGa_1-XAs thin layer, the coupled modes consist of three branches of the high, intermediate and low frequency modes. Their frequencies depend on both concentration and alloy composition. To analyses the surface polariton modes we carry out attenuated total reflection (ATR) measurements. In order to support our assignment the magnetic field profiles and surface polariton dispersion curves have been calculated.     

Interface phonons in cylindrical quantum dot heterostructure

The top interface optical (TIO) and side interface optical (SIO) phonon modes of a cylindrical GaAs/ Al_xGa_1−xAs quantum dot are derived within the framework of dielectric continuum approximation. Results reveal that, in the case of taking the “two-mode” behavior of the Al_xGa_1−xAs material into account, there exist eight branches of TIO phonon modes and four branches of SIO phonon modes. The dispersion frequencies of TIO or SIO phonon modes sensitively depend on the Al mole fraction x$x$ in the Al_xGa_1−xAs material. With increasing wavevector q$q$ (κ$\kappa$), the frequency of each TIO (SIO) mode approaches one of the two frequency values of the single Al_xGa_1−xAs heterostructure.     

Ternary effects on the optical interface phonons in onion-like GaN/AlxGa1 − xN quantum dots

The interface optical phonons and its ternary effects in onion-like quantum dots are studied by using dielectric continuum model and the modified random-element isodisplacement model. The dispersion relations, the electron–phonon interactions and ternary effects on the interface optical phonons are calculated in the GaN/Al_xGa_1 − xN onion-like quantum dots. The results show that aluminium concentration has important influence on the interface optical phonons and electron–phonon interactions in GaN/Al_xGa_1 − xN onion-like quantum dots. The frequencies of interface optical phonons and electron–phonon coupling strengths change linearly with increase of aluminium concentration in high frequency range, and do not change linearly with increasing aluminium concentration in low frequency range.