Directly Probing Effective-Mass Anisotropy of Two-Dimensional ReSe2 in Schottky Tunnel Transistors

Anisotropic physical properties in two-dimensional (2D) layered semiconductors with low crystal lattice symmetry are of great interest due to the underlying rich physics and potential applications in electronics. Sophisticated transport measurements unveiling the anisotropic effective mass, which is an essential material parameter reflecting the energy band, are still lacking so far. With a focus on the anisotropy with respect to the underlying crystal structure, in this work, we propose a simple strategy to directly probe the carrier effective mass ${m}^{\ensuremath{\ast}}$ for 2D semiconductors using tunneling as the sensing tool. The Schottky tunnel transistor is a practically simple device, in which the transport can be electrically tuned to be tunneling dominated. Using such a device as the experimental platform, we extract the anisotropy of the effective mass for both electrons and holes in the low symmetric ${\mathrm{Re}\mathrm{Se}}_{2}$ from the Fowler-Nordheim tunneling measured at 1.4 K. Furthermore, a colossal conductivity anisotropy of ${10}^{3}$ is observed for ${\mathrm{Re}\mathrm{Se}}_{2}$.