Research on spatially and temporally resolved spectroscopy of semiconductor quantum structures by using ulta small probe light

在本项目中，我们试图建立光谱技术来评估微观界面粗糙度，并在不受结构波动影响的情况下表征量子结构的固有光学特性。作为一种技术，我们利用局部探针光谱技术将物镜用于显微镜和光刻技术相结合，在样品顶部制造小窗口，从而提高了空间分辨率。我们选择了由化合物半导体制成的量子结构，研究了它可以提高电气和光学器件的性能。通过减小量子线和量子点等特征尺寸，尺寸波动对性能的影响变得显著。这就解释了为什么我们选择量子结构。我们发现，在InGaAs/GaAs量子阱中，一些微观电位波动所捕获的局域激子可以通过我们的技术检测到，而这些局域激子是宏观光致发光无法检测到的。通过对生长温度依赖性的测量，我们澄清了生长温度的升高导致界面陡度的恶化，这是由于In表面偏析造成的，然而，与在较低温度下生长的样品相比，界面粗糙度得到了改善。此外，我们成功地观察到量子点中的带电激子，并通过对调制掺杂量子点施加电场来控制其带电状态。此外，我们尝试创建新的量子结构来插入超薄膜作为电子的局域中心，并成功地大大提高了间接半导体的发光效率，我们发现量子点的堆叠极大地改变了生长模式。下一步，我们将把我们的光谱技术应用于这些量子结构，并阐明它们的微观结构和机制，以提高发光效率。

In this project, we have tried to establish spectroscopic technique to evaluate microscopic interface roughness, and to characterize inherent optical properties of quantum structures without being affected by structural fluctuations. As a technique, we exploited to combine local probe spectroscopy to use objective lens for microscope and lithography technique to fabricate small window on top of the sample, leading to improved spatial resolution.We selected quantum structures made from compound semiconductors, which are studied to improve electrical and optical device performance. By reducing the feature sizes such as quantum wires and quantum dots, the impact of the size fluctuations on the properties becomes significant. This explains why we selected the quantum structures.We found that localized excitons trapped by some microscopic potential fluctuations in InGaAs/GaAs quantum wells, which are not detected by macroscopic photoluminescence, can be detected by our technique. By measuring growth teroperature dependence, we clarified that the increase of the growth temperature lead to the deterioration of the interface abruptness due to the In surface segregations, however, the interface roughness is improved compared to the sample grown at lower temperatures. In addition, we succeeded in observing charged excitons in quantum dots and controlling the charged states by applying electric field to modulation-doped quantum dots.Furthermore, we tried to create novel quantum structures to insert ultra thin film as a localized center for electrons, and succeeded in improving drastically improve the luminescence efficiency of indirect semiconductors, and we found that stacking of quantum dots greatly modify the growth mode. As a next step, we will apply our spectroscopic technique to these quantum structures and clarify their microscopic structures and mechanisms for improved luminescence efficiency.