First-Principles Study of the Schottky Contact, Tunneling Probability, and Optical Properties of MX/TiB₄ 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 4 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 4 heterojunctions. The calculated binding energies reveal that X-type MX/TiB 4 heterojunctions exhibit more stable structures than M- and C-type stacking modes. Schottky barrier heights (SBHs) indicate that X-type GeSe/TiB 4 and GeTe/TiB 4 form n-type Schottky contacts with SBHs of 0.497 and 0.132 eV, respectively, while SnS/TiB 4 and SnSe/TiB 4 form p-type Schottky contacts with SBHs of 0.557 and 0.418 eV, respectively. Moreover, X-type MX/TiB 4 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 4 heterojunctions is also observed compared with individual TiB 4 and MX monolayers. By applying in-plane biaxial strain, the transformation of MX/TiB 4 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.