Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers
Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers
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DOI：
10.1103/physrevb.84.035313
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发表时间：
2011-07-26
影响因子：
3.7
通讯作者：
Meyer, B. K.
中科院分区：
文献类型：
--
作者：
Wagner, M. R.;Callsen, G.;Meyer, B. K.
氧化锌单晶、外延层和纳米结构通常在3.33 eV到3.35 eV的光谱范围内表现出各种窄的发射线，这些发射线通常被归因于深度束缚激子(Y线)。在这项工作中，我们对深束缚激子的性质进行了全面的研究，特别是在3.333 eV的Y-0跃迁。将这些中心的电学和光学性质与浅杂质相关激子结合中心(I线)的电学和光学性质进行了比较。与氧化锌中的浅施主相比，深束缚激子复合体的热激活能和激子局域能相差很大，不能用有效质量方法来描述。浅束缚激子和深束缚激子之间的不同性质也反映在深中心与晶格声子之间的极小耦合以及它们的两个电子卫星跃迁之间的小分裂上。基于磁光致发光、磁吸收、激发光谱(PLE)、时间分辨光致发光(TRPL)和单轴压力测量等多种不同的实验结果，建立了一个定性的缺陷模型，该模型将所有Y线解释为与扩展的结构缺陷复合体结合的激子的辐射复合。这些缺陷复合体在氧化锌中引入了额外的施主状态。此外，单色阴极发光成像显示了缺陷中心的空间局域化特征，与浅杂质中心的均匀分布形成对比。讨论了缺陷束缚激子与氧化锌绿色发光带之间的可能关系。将缺陷跃迁的光学性质与其他II-VI和III-V半导体中与缺陷和位错束缚激子有关的类似发光线进行了比较。
ZnO single crystals, epilayers, and nanostructures often exhibit a variety of narrow emission lines in the spectral range between 3.33 and 3.35 eV which are commonly attributed to deeply bound excitons (Y lines). In this work, we present a comprehensive study of the properties of the deeply bound excitons with particular focus on the Y-0 transition at 3.333 eV. The electronic and optical properties of these centers are compared to those of the shallow impurity related exciton binding centers (I lines). In contrast to the shallow donors in ZnO, the deeply bound exciton complexes exhibit a large discrepancy between the thermal activation energy and localization energy of the excitons and cannot be described by an effective mass approach. The different properties between the shallow and deeply bound excitons are also reflected by an exceptionally small coupling of the deep centers to the lattice phonons and a small splitting between their two electron satellite transitions. Based on a multitude of different experimental results including magnetophotoluminescence, magnetoabsorption, excitation spectroscopy (PLE), time resolved photoluminescence (TRPL), and uniaxial pressure measurements, a qualitative defect model is developed which explains all Y lines as radiative recombinations of excitons bound to extended structural defect complexes. These defect complexes introduce additional donor states in ZnO. Furthermore, the spatially localized character of the defect centers is visualized in contrast to the homogeneous distribution of shallow impurity centers by monochromatic cathodoluminescence imaging. A possible relation between the defect bound excitons and the green luminescence band in ZnO is discussed. The optical properties of the defect transitions are compared to similar luminescence lines related to defect and dislocation bound excitons in other II-VI and III-V semiconductors.