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Low temperature near-field optical mapping and control of electron wavefunctions confined in nanostructures

纳米结构中限制的电子波函数的低温近场光学测绘和控制

基本信息

批准号：
16310075
负责人：
SAIKI Toshiharu
金额：
$ 8.9万
依托单位：
Keio University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

We have established a near-field scanning optical microscope (NSOM) system with a high spatial resolution under a magnetic field up to 5T at low temperature. The spatial resolution as high as 30-50 nm enabled us to visualize exciton wave functions confined in single quantum dots.In GaAs/AlGaAs interface quantum dots, the wavefunctions of ground-state exciton, excited-state exciton, and biexciton states are clearly mapped out. A numerical calculation reproduced the experimental results well in their quantitative nature. We also applied this technique to visualize the local density of states of excitons confined in an electric-field induced quantum dot system. We observed that electrons confined in lower energy states localized more strongly.Dilute nitride alloy systems such as GaNAs and GaInNAs were investigated to clarify nonuniform distribution of N atoms through the spatially resolved spectroscopy of localized and delocalized electron states. The depths and spatial profiles of exciton confinement potential were visualized through the measurement of power-dependent PL spectra and high-resolution PL images. For two GaInNAs quantum wells with different N contents, we observed strongly localized excitons confined in N clusters and rather delocalized excitons, which indicate the onset of alloy formation.From magneto-PL spectroscopy of a single QD, a diamagnetic shift of the exciton emission was observed. Referring to the theoretical value we estimate the size of the QD from a diamagnetic coefficient, which is determined by the Bohr radius of excitons confined in QDs. The result was in good agreement with that obtained by the real-space NSOM mapping.

我们建立了一套在低温磁场下具有高空间分辨率的近场扫描光学显微镜（NSOM）系统。在GaAs/AlGaAs界面量子点中，基态激子、激发态激子和双激子态的波函数被清晰地映射出来。数值计算再现了实验结果以及在其定量性质。我们还应用这种技术可视化的局域态密度的激子限制在电场诱导的量子点系统。我们观察到束缚在低能态的电子局域化程度更强，通过局域化和离域电子态的空间分辨光谱研究了稀氮化物合金系统如GaNAs和GaInNAs中N原子的非均匀分布。通过测量光致发光谱和高分辨率光致发光谱图像，得到了激子约束势的深度和空间分布。对于两个不同N含量的GaInNAs量子威尔斯，我们观察到了强的局域激子和离域激子，这表明合金的形成开始.从单个量子点的磁光致发光光谱中，我们观察到了激子发射的抗磁位移.参考理论值，我们估计的量子点的大小从抗磁性系数，这是由玻尔半径限制在量子点的激子。所得结果与实空间NSOM映射结果吻合较好。