Study of Optical and Electronic Properties of Individual Semiconductor Nano-structures

1)利用扫描隧道显微镜(STM)研究了超热电子在AlGaAs/GaAsQW结构中的输运特性。电子从STM针尖注入，距离解理的(110)表面上的靶井不同距离。然后通过测量目标势垒的发光强度，确定了注入电子的热化和扩散长度。2)利用带扫描近场光学显微镜的光致发光显微镜，研究了GaAs/InGaAs量子阱结构中失配位错的形成机制。从荧光图像中观察到的暗线密度作为总层厚度的函数，我们发现存在两个临界层厚度。考虑到晶格摩擦力与In含量成正比，解释了这两个临界层厚度。3)用截面扫描隧道显微镜研究了Ga_&lt；0.968&Gt；Mn_&lt；0.032&Gt；As的电子结构。STM图像显示明亮和黑暗区域中的亮点随机分布。由扫描隧道显微镜测量的电导谱估算出GaMnAs的禁带宽度为1.23±0.05 eV。带隙内的有限电导表明价带中存在空穴状态。在价带边缘上方0.7 eV处的附加峰可以被指定为电子隧穿进入As反位的电离能级。4)利用扫描隧道显微镜测量了InAs/AlGaAs自组装量子点的光强图像。在不同光子能量的图像中观察到了局域化的明亮特征。在明亮特征上测量的发射光谱显示出具有不同峰位的单一发射峰。通过将峰值能量与金字塔量子点结构计算的跃迁能进行比较，我们发现亮特征对应于单个InAs量子点的基态发射。

1) We have investigated the transport properties of hot electrons in AlGaAs/GaAs quantum well (QW) structures in real space using a scanning tunneling microscope (STM). The electrons were injected from the STM tip at different distances from a target well on the cleaved (110) surface. Then by measuring the light emission intensity from the target well, the thermalization and diffusion lengths of the injected electrons were determined.2) Using photoluminescence (PL) microscopy with the scanning near-field optical microscope, we have investigated the formation mechanism of misfit dislocations in GaAs/InGaAs QW structures. From the density of dark lines observed in the PL images as a function of the total layer thickness, we found that there exist two critical layer thicknesses. These two critical layer thicknesses are explained by taking account of a lattice frictional force proportional to the In content.3) Using cross-sectional STM, we have investigated the electronic structures of Ga_<0.968>Mn_<0.032>As. The STM image showed a random distribution of bright spots in light and dark areas. From conductance spectra measured with the STM, the bandgap of the GaMnAs was estimated to be 1.23±0.05 eV. Finite conductance within the band gap indicates the presence of hole states in the valence band. An additional peak at 0.7 eV above the valence band edge can be assigned to electron tunneling into the ionization levels of As antisites.4) Light intensity images of self-assembled InAs/AlGaAs quantum dots (QDs) were measured using the STM. Localized bright features were observed in the images for different photon energies. The emission spectra measured over the bright features showed single emission peaks with different peak positions. By comparing the peak energies with the transition energies calculated for pyramidal QD structures, we found that the bright features correspond to the ground-state emission from individual InAs QDs.