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

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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.