"A study on novel quantum structures utilizing direct Schottky contacts to the two dimensional electon gas"

本研究的目的是研究肖特基/2DEG接触的性质，并利用肖特基/2DEG接触作为面内栅极实现新的量子结构。取得的主要结果如下：(1)我们发展了一种新的技术，利用原位电化学方法在AlGaAs/GaAs异质结中形成了与2DEG边缘直接肖特基接触，并将该技术应用于形成面内栅型量子结构。(2)成功地制备了面内栅型量子线晶体管。在100K下观察到量子电导，表明这种新型的面内栅比传统的分裂栅结构实现了更强的电子约束。(3)制作了面内栅型电子干涉器件(Aharonov-Bohm环)。通过适当的栅极调谐，在3.3K下观察到了由于A-B干涉效应引起的明显的磁阻振荡。(4)成功地研制了面内栅单电子晶体管。所有制备的器件在低温下都表现出明显的库仑电导振荡和库仑阻塞特性。最高工作温度为30K。(5)具有双量子点的单电子晶体管表现出复杂的电导振荡行为，强烈依赖于两个量子点的耦合条件。这种行为很可能是由两个点中量子能级之间的相互耦合效应来解释的。

The purpose of this study is to investigate the properties of Schottky/2DEG contacts and to realize novel quantum structures utilizing the Schottky/2DEG contacts as in-plane gates. The main results obtained are listed below :(1) We developed a novel technique to form a direct Schottky contact to the edge of 2DEG in AlGaAs/GaAs heterojunction by use of in-situ electrochemical process, and applied this technique to formation of in-plane-gate type quantum structures.(2) In-plane-gate type quantum wire transistors were successfully fabricated. Quantized conductance was observed up to 100K,indicating that the novel in-plane gate realized stronger electron confinement than that in conventional split-gate structures.(3) In-plane-gate type electron interference device (Aharonov-Bohm ring) was also fabricated. By suitable gate tuning, clear magnetoresistance oscillation due to the A-B interference effect was observed at 3.3K.(4) GaAs based single electron transistors with in-plane gates were successfully developed. All the fabricated devices gave clear Coulomb conductance oscillation and Coulomb blockade characteristics at low temperatures. The maximum operation temperature is 30K.(5) Single electron transistors having double quantum dots exhibited complicated conductance oscillation behavior that strongly depended on the coupling condition of two dots. This behavior is likely to be explained by the inter-coupling effect between quantum levels in both dots.