Engineering of topological tunneling transistors via quantum point contact

Owing to the versatile transport process, tunneling transistors (TTs) have become important building blocks for modern electronic, optoelectronic, and magnetic technologies. Although various TTs have been developed, their device operation still has challenges in terms of stability and reliability due to the tunneling process being susceptible to material size and interface scatterings. The robust edge channels in a topological insulator (TI) hold novel tunneling physics, but their TTs are still lacking. In this theoretical work, we propose topological tunneling and resonant TTs by using edge states (ESs) as transport channels in the quantum point contact (QPC) constriction. The finite size effect is the key to adjusting the band structure and tunneling barrier height of ESs by controlling the QPC width. By using the Bernevig-Hughes-Zhang (BHZ) model, we explore the single-QPC tunneling and double-QPC resonant tunneling transport, as well as their device characteristics via the quantum transport Kwant package. Topological TTs based on a single QPC possess excellent gate-modulated capability as well as a size-dependent current sensitivity of $0.1\phantom{\rule{0.1em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}1}$, several orders of magnitude lower than the conventional TTs. The transport results show that the tunneling probability is significantly influenced by the QPC width (barrier height) but is weakly dependent on the QPC length (barrier width). Moreover, topological resonant TTs are designed in a double-QPC structure and show a negative differential resistance with a large peak-valley current ratio $(>{10}^{4})$. The transmission spectrum exhibits multiple peaks due to the resonant tunneling driven by quantum well states. The distance between two QPCs can shift these resonant peaks by modulating the transverse confined effect. This study opens a window for designing stable, reliable, and high-performance tunneling devices via emerging quantum materials with great potential for low-power topological electronics applications.