Formation and Characterization of High Density Semiconductor Quantum Dots

我们开发了一种通过选择性面积金属有机气相外延（SA-MOVPE）生长形成位置和尺寸控制的量子线（QWRs）和量子点（QDs）的技术。该技术已被应用于直接制造单电子晶体管和使用量子点-量子水阱耦合结构的电路。项目的主要成果总结如下。(1)研究了SA-MOVPE制备高密度均匀量子点阵列的机理。我们发现并阐明了SA-MOVPE中的自限机制，即GaAs金字塔结构和脊状结构在形成三维结构后仍保持顶部尺寸和形状。利用这种自限生长方式实现量子点的尺寸均匀性。我们还澄清了GaAs金字塔的顶部尺寸是由台阶边缘吸附和解吸原子之间的平衡决定的，并且可以由生长条件控制。(2)基于量子点阵列的织构化技术，我们提出并成功利用SA-MOVPE技术制备了量子点和量子水阱的二维耦合阵列。光学表征证实了量子点和量子水阱形成了网状阵列。结果表明，我们提出的制造方法可以有效地实现未来电子产品中单电子晶体管等量子器件的高密度集成。(3)将SA-MOVPE技术形成的QWR-QD-QWR耦合结构与肖特基栅技术相结合，成功制备了单电子晶体管。我们成功地演示了单电子逆变器的电路操作，该逆变器集成了量子线晶体管和在设计的SA-MOVPE掩膜衬底上一步生长的单电子晶体管。我们的量子点器件还显示出强大的横向约束，这有利于探索纳米结构的物理特性，例如量子点中的近藤效应。少

We have developed a technique to form position-and size-controlled quantum wires (QWRs) and quantum dots (QDs) by selective area metalorganic vapor phase epitaxial (SA-MOVPE) growth. The technique is applied for the direct fabrication of single electron transistors and circuits using QD-QWR coupled structures. Main results of the project are summarized below.(1) We investigated the mechanism of SA-MOVPE for the fabrication of high-density QD arrays with extreme uniformity. We have found and clarified the self-limited mechanism in SA-MOVPE where the top size and shape of the GaAs pyramidal structures and ridge structures are maintained after the formation of such 3-dimensional structures. This self-limited growth mode is utilized to achieve size uniformity in QDs. We also have clarified that the top size of the GaAs pyramid is determined by the balance between the adsorption and desorption of adatoms at the step edges and can be controled by the growth conditions.(2) Based on the fabric … More ation technique of QD arrays, we have proposed and succes sfully fabricated a two-dimensional coupled array of QDs and QWRs by SA-MOVPE.The optical characterization has confirmed the formation of network-like array of QDs and QWRs. The results indicate that our proposed fabrication method is effective to realize high-density integration of quantum devices, such as single electron transistors, for future electronics.(3) Single electron transistors have successfully been fabricated by the combination of coupled structures of QWR-QD-QWR formed by SA-MOVPE technique and Schottky gate technology. We have succeeded in the demonstration of the circuit operation of single electron inverters, which integrates quantum wire transistor and single electron transistors fabricated by one-step growth on designed masked substrate for SA-MOVPE.Our quantum dot devices also have shown to exhibit strong lateral confinement that are beneficial to explore the physics of nanostructures, such as Kondo effect in QDs. Less