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AlGaAs/GaAs量子阱（QW）结构中超热电子在真实的空间中的输运性质。电子从STM针尖在离解理（110）表面上的靶阱不同的距离处注入。通过测量靶阱的发光强度，确定了注入电子的热化长度和扩散长度。2）利用扫描近场光学显微镜和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PL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。这两个临界层厚度是通过考虑晶格摩擦力与In含量成正比来解释的。3）用截面STM研究了Ga_ Mn_ As的电子结构<0.968><0.032>。STM图像显示亮斑在亮区和暗区的随机分布。从STM测量的电导谱，GaMnAs的带隙估计为1.23±0.05 eV。带隙内的有限电导表明价带中存在空穴态。在价带边缘以上0.7 eV处的另一个峰可以归因于电子隧穿进入As反位的电离能级。4）使用STM测量了自组装InAs/AlGaAs量子点（QD）的光强图像。在不同光子能量的图像中观察到局部明亮的特征。在明亮特征上测量的发射光谱显示具有不同峰位置的单个发射峰。通过比较金字塔量子点结构的峰值能量与跃迁能量，我们发现明亮的特征对应于单个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.