InAs/GaSb/AlSB 2D topological insulator materials and devices

本提案的总体目标是研究InAs/GaSb耦合量子阱中的拓扑绝缘体相位和TI基器件的实现。为此，利用分子束外延对InAs/GaSb结构的生长进行优化。这将包括在不同衬底（GaAs和GaSb）上的生长，以及通过系统地改变生长条件来优化界面结构。该提案的第二个目标是开发双面门控InAs/GaSb量子阱的制造工艺。基于GaSb的层结构具有许多在器件加工中必须注意的特性，例如氧化时导电表面层的形成。因此，技术的发展将包括表面钝化方法的研究以及定义触点和双栅的不同方法。除了用于基本表征的简单霍尔杆外，还将研究更复杂的几何形状，如条纹或圆门。这些结构利用了随着栅极电压调整相变的可能性，因此可以实现不同相位彼此相邻的复杂景观。输运测量将用于研究InAs/GaSb样品中的剩余体积电导率，不同相位之间的栅极感应开关和环中的持续电流。该项目还将研究实现拓扑绝缘体场效应晶体管的可能性，该晶体管可以从正常绝缘状态切换到电流由边缘通道携带的几乎无耗散状态。

The overall objective of this proposal is the investigation of the topological insulator phase in InAs/GaSb coupled quantum wells and the realization of TI based devices. To this end, the growth of InAs/GaSb structures with molecular beam epitaxy will be optimized. This will include growth on different substrates (GaAs and GaSb) and the optimization of the interface configuration by a systematic variation of the growth conditions. The second objective of the proposal is the development of a fabrication processes for double-side gated InAs/GaSb quantum wells. GaSb based layer structures have a number of peculiarities that have to be taken care of in device processing, e.g. the formation of conductive surface layers when oxidized. The technology development will therefore include the study of passivation methods for the surface and different approaches for the definition of the contacts and double gates. Besides simple Hall-bars for basic characterization, more complex geometries such as stripes or circular gates will be investigated. These structures make use of the possibility to tune the phase transition with the gate voltage, and therefore allow the realization of complex landscapes where different phases are located next to each other. Transport measurements will be used to study the residual bulk conductivity in InAs/GaSb samples, gate induced switching between different phases and persistent currents in rings. The project will also investigate the possibility to realize of topological insulator FET which can be switched from a normal insulating state to a nearly dissipationless state where the current is carried by the edge channels.