Tunnel field-effect transistors for sensitive terahertz detection

The rectification of high-frequency electromagnetic waves to direct currents is a crucial process for energy harvesting, beyond 5G wireless communications, ultra-fast science, and observational astronomy. As the radiation frequency is raised to the sub-terahertz (THz) domain, efficient ac-to-dc conversion by conventional electronics becomes increasingly challenging and requires alternative rectification protocols. Here we address this challenge by tunnel field-effect transistors made of dual-gated bilayer graphene (BLG). Taking advantage of BLG's electrically tunable band structure, we create a lateral tunnel junction and couple it to a broadband antenna exposed to THz radiation. The incoming radiation is then down-converted by strongly non-linear interband tunneling mechanisms, resulting in exceptionally high-responsivity (exceeding 3 kV/W) and low-noise (0.2 pW/$\sqrt{Hz}$) detection at cryogenic temperatures. We demonstrate how the switching from intraband Ohmic to interband tunneling regime within a single detector can raise its responsivity by one order of magnitude, in agreement with the developed theory. Our work demonstrates an unexpected application of interband tunnel transistors for high-frequency detection and reveals bilayer graphene as one of the most promising platforms therefor.