【作者】 羊亿；

【导师】 申德振；

【作者基本信息】 中国科学院长春光学精密机械与物理研究所 ， 凝聚态物理， 2001， 博士

【摘要】 半导体量子点由于三维量子限域效应导致其类原子分立能级结构的存在，可望得到性能优异的新型光电器件。如以量子点作为激活层的激光器与量子阱激光器相比有更低的阈值电流，更高的增益和特征温度。Stranski-Krastanow模式（S—K模式）自组装量子点（SAQD）由于制备方法简单、无位错缺陷等特性而成为目前制备高质量量子点的主要方法。但由于目前对量子点自组装机理并不是很清楚，尤其是Ⅱ—Ⅵ族材料，即使对于研究得较多的CdSe/ZnSe材料系统也存在许多争议。因而导致其尺寸、形状、分布均匀性和密度难以控制。虽然目前对SAQD的垂直有序化、尺寸均匀性和自排列有一定的研究，但结果还不尽如人意。因此要想能真正地控制SAQD的生长还得从其最基本的生长机理入手。 研究量子点自组装机理的最好方式是直接观测量子点的自组装形成过程。原子力显微镜（AFM）为直接观测表面形貌的有力工具，但由于AFM不能提供原位监测，所以一般只能用于表征量子点的形貌或研究量子点的熟化展宽过程。 本论文利用AFM监测了自组装CdSe量子点的形成过程，并系统研究了自组装CdSe量子点的形成机理，主要取得了以下结果：1、利用LP—MOCVD生长了高质量的自组装CdSe量子点。利用AFM研究了自组装CdSe量子点的形成，并首次观测到了SAQD的形成过程。把SAQD能在低于临界厚度的外延层中形成归因于表面扩散与应变释放共同作用的结果。提出了利用表面扩散的慢过程补偿AFM测量所需的时间，从而利用AFM来研究自组装量子点形成机理的想法。2、利用AFM系统研究了自组装CdSe量子点的形成机理。提出了在低于临界厚度状态下SAQD形成的竞争机理，其中包括表面扩散导致的应变释放形成SAQD及表面粗糙化诱发的位错成核两种竞争过程。该机理能很好地解释目前存在于自组装CdSe量子点研究领域中的许多争议，并对进一步生长高质量SAQD有一定指导作用。3、通过对自组装 Cdse量子点的光学特性研究，进一步证实了 SAQD的形成。研究了在Znse基质中Cdse超薄层的光学特性，并认为界面扩散不利于外延层应变释放形成自组装量子点。更多还原

【Abstract】 Semiconductor quantum dot structures, with atomic-like discrete energy states, are expected to improvement novel application in optical and electronic device, due to the three dimensional confinement on the carriers or excitons. Compared to lithographic methods, the Stranski-Krastanow mode (S-K mode) is a promising method, which doesn need complicated fabrication techniques and which achieves high optical quality due to low interface defects. However, the formation mechanism of self-assembled quantum dots (SAQD) is not very clear until now especially for lI-VT quantum dots such as CdSe/ZnSe. Hence, it is very difficult to control the growth of SAQD. Although there have some researches on how to control the size, density of SAQD, the results are not satisfied. Moreover, the formation mechanism of SAQD has attracted our interest not only for fabricating top- quality quantum dots to novel devices but also from the point of view of basic science. To study the formation mechanism of SAQD, the best way is to observe the formation process directly. Atomic force microscopy (AFM) is an effective instrumentation to get direct information of the surface morphology. However, AFM can be used as in-situ instrumentation. Hence, AFM usually be used to characterize the morphology or the ripening process of quantum dots. In this thesis, we observed the formation process of CdSe SAQD and studied the formation mechanism of CdSe SAQD systematically by AFM. The following is the major results: 1. High quality Self-assembled CdSe quantum dots were fabricated by low- pressure metalorganic chemical vapor deposition (LP-MOCVD) system. The formation process of SAQD was observed by AFM for the first time. The formation of CdSe SAQD under critical thickness was due to the effect of surface diffusion and strain release. The slow process of surface diffusion can compensate for the time that is needed for AFM. These results make it possible to directly observe the process of release strain and to obtain the actual information on the formation process of self- assemb led quantum dots by AFM. 2. The formation process of CdSe SAQD was investigated systematically by AFM. It revealed that the relaxation of misfit strain is completed by two competing processes. One is the formation of quantum dots assisted by surface diffusion; another is the formation of misfit dislocations. The surface roughness can allow easy to nucleation of misfit dislocations. This competitive mechanism can explain many discussing issues existed in the formation of CdSe SAQD. 3. The optical properties of CdSe SAQD and CdSe ultrathin layer were studied. The formation of SAQD was verified by the research of optical properties. The interface diffusion can release part of misfit strain and go against the formation of SAQD.更多还原