First-Principles Study of the Schottky Contact, Tunneling Probability, and Optical Properties of MX/TiB Heterojunctions (M = Ge, Sn; X = S, Se, Te): Strain Engineering Tunability.

Designing two-dimensional (2D) heterojunctions with rapid response and minimal energy consumption holds immense significance for the advancement of the next generation of electronic devices. Here, we construct a series of Schottky heterojunctions based on TiB monolayer and group-IV monochalcogenide monolayers MX (M = Ge, Sn; X = S, Se, Te). Using first-principles calculations, we investigate the structural stability, Schottky contact barrier, tunneling probability, and optical properties of MX/TiB heterojunctions. The calculated binding energies reveal that X-type MX/TiB heterojunctions exhibit more stable structures than M- and C-type stacking modes. Schottky barrier heights (SBHs) indicate that X-type GeSe/TiB and GeTe/TiB form n-type Schottky contacts with SBHs of 0.497 and 0.132 eV, respectively, while SnS/TiB and SnSe/TiB form p-type Schottky contacts with SBHs of 0.557 and 0.418 eV, respectively. Moreover, X-type MX/TiB heterojunctions exhibit high susceptibility to interlayer electron tunneling due to their large tunneling probability and strong interlayer interaction. Meanwhile, enhanced optical absorption capacity in MX/TiB heterojunctions is also observed compared with individual TiB and MX monolayers. By applying in-plane biaxial strain, the transformation of MX/TiB heterojunctions from a Schottky contact to an Ohmic contact can also be realized. Our findings could offer valuable candidate materials and guidance for the design of the next generation of nanodevices with high electronic and optical performances.