Study of resonant tunneling through single quantum dots by atomic force microscopy

1.用新型量子点电极探测单个InAs量子点的共振隧穿用带有导电针尖的原子力显微镜（AFM）观察了电子隧穿单个自组装InAs量子点（QD）的量子能级。这里采用的独特结构由两层InAs量子点组成，它们被薄的未掺杂GaAs阻挡层隔开。当导电尖端接触时，裸露的表面InAs QD起到纳米级电极的作用，来自n^+-GaAs衬底的电子通过掩埋的QD流动。在120 K下获得的电流-电压特性数据中，根据顶部InAs纳米电极的尺寸，在不同的偏置电压下观察到谐振峰。这是由于InAs量子点上的表面电位的尺寸依赖性。用分子束外延技术控制InAs量子点的尺寸和密度 ...更多信息 分子束外延高度发展以控制它们的尺寸和密度。也就是说，通过精确控制生长条件，InAs量子点的尺寸和密度分别在15 ~ 45 nm和100 ~ 100 μ cm <11>~ 2<-2>之间变化.通过嵌入微型RTD中的单个InAs量子点的共振隧穿，这种生长控制不仅是上述双层InAs量子点结构的制备所必需的，而且实现了其中仅包含一个量子点的微型共振隧穿二极管。具有嵌入在顶部GaAs层中的极低密度（104x10^8 cm^<-2>）InAs量子点的GaAs晶片。由于通过电子束光刻和化学蚀刻形成的二极管的尺寸为1μm^2，并且每个二极管的边缘都被耗尽，因此每个二极管所包含的有源Ods的数量可以减少到平均小于1。使用导电针尖AFM在130 K下进行了电流-电压测量，并成功地观察到由电子共振隧穿单个量子点能级引起的电流峰。少

1. Resonant tunneling through a single InAs quantum dot probed via novel over layered quantum dot electrodeElectrons tunneling through the quantum levels of a single self-assembled InAs quantum dot (QD) have been observed using an atomic force microscope (AFM) with a conductive tip. The unique structure employed here consists of two layers of InAs QDs, which were separated by thin undoped GaAs barrier layer. When the conductive tip is in contact, the naked surface InAs QD functions as a nanoscale electrode to where electrons from the n^+-GaAs substrate flow via a buried QD. In the current-voltage characteristics data taken at 〜120 K, resonance peaks are observed at different bias voltages depending on the size of the top InAs nano-electrodes. This is due to the size dependence of the surface potential on the InAs QDs.2. Control of the size and density of InAs quantum dots by molecular beam epitaxyFor the purpose of the resonant tunneling measurement, the InAs QD growth technique by mol … More ecular beam epitaxy was highly developed to control their size and density. Namely, we demonstrated the size and density of InAs QDs are changed from 15 to 45 nm and from 〜10^8 to 〜10^<11> cm^<-2>, respectively by precise control of the growth conditions.3. Resonant tunneling through a single InAs quantum dot embedded in a micro RTDThis growthcontrol is not only essential for the fabrication of the above-mentioned double layered InAs QD structure but also have realized a micro resonant tunneling diode which contains only one QD in it. We also studied resonant tunneling transport of electrons through a single InAs QD by forming a micron-size Schottky diode in a GaAs/n+-GaAs wafer with very low density (〜4x10^8 cm^<-2>)InAs QDs embedded in the top GaAs layer. As the diode defined by electron beam lithography and chemical etching has a size of 〜1μm^2 and the edges of each diode are depleted, the number of active Ods contained each diode can be reduced to less than unity in average. Current-voltage measurements were performed using a conductive-tip AFM at 〜130 K, and current peaks caused by electrons resonantly tunneling through the energy levels of single QDs were successfully observed. Less