Spin-Filtered Tunneling Device Using a Topological Insulator

There has been much interest in the study of topological insulators (TI) recently. Due to their unique electronic structure, these new materials have been an active area of research to discover new quantum phenomena and their application in new technologies. Unlike the electronic structure observed in traditional semiconductors, the strong spin-orbit coupling induces a band inversion in the electronic structure of TIs. One of the side effects of this band inversion is creating metallic-like surface states at the material's surface that are protected by time invariance and whose spin angular momentum is locked to the direction of the momentum of the electron.

These surface states are essentially resistant to scattering events that otherwise affect other materials. Leveraging the characteristic scattering resistance, the spin-momentum locking of the surface states, and the Dirac cone structure, a spin-resonant tunneling diode using topological insulators has been investigated to implement a negative differential resistance device. Utilizing the spin texture of the surface states, an additional spin-filter can help to suppress the valley current in a negative differential resistance device. In the spin-resonant tunneling diode, the tunneling process would also benefit from having protection from conventional scattering processes due to defects and thickness or line edge roughness.

This research is focused on the manufacturing of a spin-filtered tunnel diode. Using molecular beam epitaxy to grow a three-layer heterostructure, with two layers of bismuth selenide as the topological insulator separated by a thin layer of tungsten diselenide as a tunnel barrier. The alignment of the Fermi levels of the topological insulator layers and the thickness of the tunnel barrier were investigated using X-ray Photoelectron Spectroscopy. The fabrication and initial electrical measurements of the spin-filtered tunnel diode were also investigated.