内建电场对GaN/AlGaN单量子点发光性质的影响

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,研究了GaN/AlGaN单量子点发光性质随量子点结构参数(量子点高度L和量子点半径R)的变化。结果表明:内建电场对GaN/AlGaN单量子点的发光波长和激子基态振子强度等发光性质有重要的影响;量子点高度的变化对量子点发光性质的影响要比量子点半径的变化对量子点发光性质的影响更明显。     

纤锌矿InxGa1-xN／GaN量子阱中的界面声子-电子相互作用

在介电连续模型下,运用传递矩阵的方法研究了任意层纤锌矿量子阱中界面光学声子的电声相互作用,得出了任意层纤锌矿量子阱中界面光学声子与电子相互作用的哈密顿。结果表明,在对称单量子阱GaN／InxGa1-xN／GaN中,界面声子-电子相互作用的耦合强度随组分x的变化差别很大;在对称单量子阱GaN／In0.8Ga0.2N／GaN中,不同的界面声子随着波数的变化对电声相互作用的贡献不同。     

纤锌矿GaN量子点中相关电子空穴的光跃迁：应变和流体静压力效应

在有效质量和有限高势垒近似下,变分研究了应变和流体静压力对纤锌矿GaN/AlxGa1-xN柱形量子点中激子发光波长和电子空穴复合率的影响。计算结果表明,在量子点高度较大情况下( >3.8 nm ),考虑应变后的发光波长比不考虑应变的发光波长大。而在量子点高度较小情况下( <3.8 nm )则相反。由于应变效应,为了获得有效的电子、空穴复合过程,GaN量子点的高度必须小于5.5nm。发光波长随流体静压力的增大而线性减小,电子空穴复合率随流体静压力的增大而近线性增大。在量子点尺寸较大的情况下,流体静压力对发光波长的影响比较显著,而在量子点尺寸较小的情况下,流体静压力对电子空穴复合率的影响比较显著。此外,我们将零流体静压力下光跃迁能的理论计算值和实验值进行了比较,理论值和实验值相符合。     

纤锌矿InxGa1-xN/GaN量子阱中的界面声子模

采用赝原胞模型计算讨论纤锌矿InxGa1-xN混晶性质;基于宏观介电连续模型的传递矩阵方法研究任意层纤锌矿量子阱中的界面声子,得出任意层纤锌矿量子阱中的界面声子的本征模解和单量子阱的色散关系,并对InxGa1-xN/GaN单量子阱界面声子的色散关系进行了数值计算和讨论。结果表明,纤锌矿InxGa1-xN混晶中的E1声子和A1声子都表现为单模行为;在对称非应变单量子阱GaN/InxGa1-xN/GaN中,界面声子频率随x的变化呈线性关系。     

耦合GaN/AlxGa1-xN量子点中的激子特性

在有效质量近似下，运用变分方法，考虑到量子点内电子和空穴的三维束缚以及由压电极化和自发极化所引起的内建电场，对圆柱型耦合GaN量子点的光学性质及激子态做了研究。给出了激子结合能Eb、量子点发光波长λ、电子-空穴复合率和量子点高度L^GaN以及势垒层厚度L^AlGaN之间的函数关系。结果表明，量子点高度LG^GaN、势垒层厚度L^AlGaN的增加将导致激子结合能、电子-空穴复合率的降低，耦合量子点发光波长的增加。     

InGaN/GaN多量子阱的变温发光特性研究

采用低压金属有机化学沉积方法制备了InGaN/GaN多量子阱.变温PL测量发现,量子阱发光强度具有良好的温度稳定性,随着温度升高(10～300K),发光强度只减小到1/3左右.分析认为,InGaN/GaN多量子阱的多峰发光结构是由多量子阱的组分及阱宽的不均匀引起的.随着温度升高,GaN带边及量子阱的光致发光均向低能方向移动,但与GaN带边不同,量子阱发光峰值变化并不与通过内插法得到的Varshni经验公式相吻合,而是与InN带边红移趋势一致,分析了导致这种现象的可能因素.还分析了量子阱发光寿命随温度升高而减小的原因.     

纤锌矿应变GaN柱形量子点中离子受主束缚激子的带间光跃迁

在有效质量近似基础上,考虑强的内建电场效应,变分计算了纤锌矿结构的GaN柱形量子点中带电量为 的离子受主束缚激子(A?, X)的发光波长。结果表明,离子受主束缚激子发光波长强烈依赖于量子点的尺寸（高度和半径）、离子受主杂质的位置和垒中Al含量。随着量子点高度、半径及垒中Al含量的增加,离子受主束缚激子发光波长增大。随着离子受主杂质从量子点左边垒中沿z轴方向移至量子点左边界时,发光波长先增大,在量子点的左界面附近达到极大值;随着离子受主杂质在量子点内继续右移,发光波长减小,当杂质位于量子点的右边界附近时光跃迁波长达到极小值;进一步右移离子受主杂质至量子点的右边垒中时,发光波长增大。和自由激子光跃迁波长相比,当离子受主杂质位于量子点中心的左边时,杂质的引入使发光波长增大,当离子受主杂质位于量子点中心的右边时,杂质的引入使发光波长减小。     

GaN／AIN量子点结构中的应变分布和压电效应

从Ⅲ-Ⅴ族氮化物半导体压电极化对应变的依赖关系出发，采用有限元方法计算了GaN／AIN量子点结构中的应变分布，研究了其自发极化、压电极化以及极化电荷密度．结果表明，应变导致的压电极化和Ⅲ-Ⅴ族氮化物半导体所特有的自发极化将导致电荷分布的变化，使电子聚集在量子点顶部，空穴聚集在量子点下面的湿润层中，在量子点结构中产生显著的极化电场，并讨论了电场的存在对能带带边的形状以及能级分布的影响．     

InGaN绿光LED中p型GaN层的优化设计

InGaN绿光LED的量子阱结构具有较高的In含量,InN与GaN之间较大的晶格失配度使得该结构的稳定性下降.由于量子阱结构生长完成之后的p型GaN的生长温度要远高于量子阱结构生长温度,因此,p型GaN的生长过程对多量子阱质量有重大影响.论文探讨了p型GaN的生长温度与厚度对绿光LED的材料结构及器件性能的影响.研究发现,p-GaN过高的生长温度和过大的厚度都能加剧多量子阱结构中In组分的波动,使得发光峰宽化,同时降低绿光量子阱的发光效率.论文据此提出了优化的p型GaN生长温度与厚度,探讨了量子阱保护层对InGaN绿光LED性能的影响,该结构有利于增强绿光LED发光波长的稳定性.     

GaN{11-22}半极性面上生长InGaN/GaN多量子阱的研究

利用选择性横向外延技术生长{11-22}半极性面GaN模板,并利用半极性面模板生长InGaN/GaN多量子阱结构。结果表明,生长出的GaN模板由半极性面{11-22}面和c面组成,多量子阱具有390nm和420 nm的双峰发光特性,局域阴极发光(CL)测试表明390 nm附近的发光峰来源于半极性面上的量子阱发光,而420 nm左右的发光峰源于c面量子阱发光。c面量子阱发光相对于斜面量子阱发光发生显著红移是因为在选择性横向外延生长过程中,In组分相比Ga较易从掩模区域向窗口中心区域迁移,形成了中心高In组分的c面量子阱,而半极性面上InGaN/GaN多量子阱量子限制斯塔克效应相比于极性面会减弱,此外,相同生长条件下半极性面的生长速率低于极性c面的生长速率。     

耦合GaN/AlxGa1-xN量子点的非线性光学性质

在有效质量和偶极矩近似下,考虑了由于压电极化和自发极化所引起的内建电场和量子点的三维约束效应,对纤锌矿对称Al_xGa_(1-x)N/GaN/Al_xGa_(1-x)N/GaN/Al_xGa_(1-x)N圆柱型应变耦合量子点中激子非线性光学性质进行了研究。计算结果表明,内建电场使吸收光谱向低能方向移动,发生红移现象,并且使吸收峰强度大大减小。量子限制效应使光吸收峰强度随着量子点尺寸的减小而增强,并且随着量子点尺寸的减小,吸收光谱发生蓝移现象。     

Influence of strain on hydrogenic impurity states in a GaN/ Al_xGa_(1-x)N quantum dot

Within the effective-mass approximation, we calculated the influence of strain on the binding energy of a hydrogenic donor impurity by a variational approach in a cylindrical wurtzite GaN/AlxGa1-xN strained quantum dot, including the strong built- in electric field effect due to the spontaneous and piezoelectric polarization. The results show that the binding energy of impurity decreases when the strain is considered. Then the built-in electric field becomes bigger with the Al content increasing and the bin...     

内建电场和杂质对双电子柱形量子点系统束缚能的影响

在有效质量近似下,采用变分法,研究了内建电场和杂质对双电子柱形GaN/AlxGa1-xN量子点系统束缚能的影响。结果表明：杂质带负电时,体系基态能量都比较大,不易形成稳定的束缚态。带电量为e的施主杂质位于量子点中心时,杂质电子的束缚能随量子点高度和半径的增加先缓慢增大后减小,存在最大值;随着Al含量的增加,体系的束缚能增大。随着杂质从量子点下界面沿z轴移至上界面,体系的束缚能先增大后减小。与单电子杂质态相比,内建电场对双电子量子点系统束缚能的影响比较显著;当量子点高度L<6nm时,杂质双电子量子点系统的束缚能大于单电子杂质态束缚能,而当量子点高度L>6nm时,杂质双电子量子点系统的束缚能小于单电子杂质态束缚能。     

Bound polaron in a strained wurtzite GaN/Aix Ga1-xN cylindrical quantum dot

Within the effective-mass approximation, a variational method is adopted to investigate the polaron effect in a strained GaN/AlxGa1-xN cylindrical quantum dot. The electron couples with both branches of longitudinal optical-like (LO-like) and transverse optical-like (TO-like) phonons and the built-in electric field are taken into account. The numerical results show that the binding energy of the bound polaron is reduced obviously by the polaron effect on the impurity states. Furthermore, the contribution of LO-like phonons to the binding energy is dominant, and the anisotropic angle and Al content influence on the binding energy are small.     

Bound polaron in a strained wurtzite GaN/Al_xGa_(1-x)N cylindrical quantum dot

Within the effective-mass approximation,a variational method is adopted to investigate the polaron effect in a strained GaN/Al_xGa_1-xN cylindrical quantum dot.The electron couples with both branches of longitudinal optical-like（LO-like）and transverse optical-like（TO-like）phonons and the built-in electric field are taken into account.The numerical results show that the binding energy of the bound polaron is reduced obviously by the polaron effect on the impurity states.Furthermore,the contribution of LO-like phonons to the binding energy is dominant,and the anisotropic angle and Al content influence on the binding energy are small.     

Visible InGaN/GaN Quantum-Dot Materials and Devices

General properties of III-V nitride-based quantum dots (QDs) are presented, with a special emphasis on InGaN/GaN QDs for visible optoelectronic devices. Stranski-Krastanov GaN/AlN dots are first discussed as a prototypical system. It is shown that the optical transition energies are governed by a giant quantum-confined Stark effect, which is the consequence of the presence of a large built-in internal electric field of several MV/cm. Then we move to InGaN/GaN QDs, reviewing the different fabrication approaches and their main optical properties. In particular, we focus on InGaN dots that are formed spontaneously by In composition fluctuations in InGaN quantum wells. Finally, some advantages and limitations of nitride laser diodes with active regions based on InGaN QDs are discussed, pointing out the requirements on dot uniformity and density in order to be able to exploit the expected quantum confinement effects in future devices.     

氮化物耦合量子阱中的二次谐波产生极化率:压电与自发极化效应

理论考察了存在强内建电场的纤锌矿GaN/InxGa1-xN耦合量子阱体系的二次谐波产生(SHG)特性,结果发现共振SHG系数达到了10-7m/V的量级,SHG系数对耦合量子阱的结构与掺杂组份呈现非单调的依赖关系.结果还表明,通过选择小尺寸垒宽与大尺寸阱宽的耦合量子阱,并适当降低掺杂组份,可在氮化物耦合量子阱中获得较强的SHG极化率.     

Reprint of: Optical properties of wurtzite GaN/AlN quantum dots grown on non-polar planes: The effect of stacking faults in the reduction of the internal electric field

The optical emission of non-polar GaN/AlN quantum dots has been investigated. The presence of stacking faults inside these quantum dots is evidenced in the dependence of the photoluminescence with temperature and excitation power. A theoretical model for the electronic structure and optical properties of non-polar quantum dots, taking into account their realistic shapes, is presented which predicts a substantial reduction of the internal electric field but a persisting quantum confined Stark effect, comparable to that of polar GaN/AlN quantum dots. Modeling the effect of a 3 monolayer stacking fault inside the quantum dot, which acts as zinc-blende inclusion into the wurtzite matrix, results in an additional 30% reduction of the internal electric field and gives a better account of the observed optical features.     

Optical properties of wurtzite GaN/AlN quantum dots grown on non-polar planes: The effect of stacking faults in the reduction of the internal electric field

The optical emission of non-polar GaN/AlN quantum dots has been investigated. The presence of stacking faults inside these quantum dots is evidenced in the dependence of the photoluminescence with temperature and excitation power. A theoretical model for the electronic structure and optical properties of non-polar quantum dots, taking into account their realistic shapes, is presented which predicts a substantial reduction of the internal electric field but a persisting quantum confined Stark effect, comparable to that of polar GaN/AlN quantum dots. Modeling the effect of a 3 monolayer stacking fault inside the quantum dot, which acts as zinc-blende inclusion into the wurtzite matrix, results in an additional 30% reduction of the internal electric field and gives a better account of the observed optical features.