Fig 1

(a) Schematic plot of a heterojunction where 2D material stacks on bulk substrate. (b) The conventional model of the heterojunction, where both the 2D (here, transition metal ditelluride) and bulk materials (here, silicon) are extended into supercells to accommodate the lattice mismatch. (c) The small supercell model applied in this work, involving a three-step alignment from equilibrium 2D material (AX), to uniaxially (AX') and biaxially (AX'') strained 2D material, and eventually to equilibrium bulk silicon (BY). The vacuum region in AX''/BY structure is to mimic the high-k dielectric ultrathin layer in experiment."

Fig 2

A diagram of the core-level energy alignment method for SBH in AX/BY heterojunction. The steps 1–3 correspond to the same steps illustrated in Fig. 1c."

Table 1

Comparison of the equilibrium lattice constants of 2D semimetals in their hexagonal crystal system, between predictions from DFT and experimental measurements. After transforming to the orthorhombic lattice, they form heterojunction with Si(001) (a =7.68 Å, b = 3.84 Å), and lattice mismatches are also provided. A positive (negative) mismatch indicates a tensile (compressive) strain on 2D material when forming heterojunction."

Fig 3

Band structures of TMDs under strains. The strain conditions AX' and AX'' are the ones presented in Fig. 1. (a–c) Bulk IrTe2 under no strain, uniaxial strain, and biaxial strain; (d–f) Same properties for bulk NiTe2; (g–i) Same properties for bulk PdTe2; (j–l) Same properties for bulk PtTe2; (m–o) Same properties for bulk ZrTe2."

Fig 4

(a) Energy levels of Si (black solid lines) and the Fermi level of IrTe2 (orange solid line) in the large supercell model, calculated using HSE and only Γ point. (b) The projected DOS of Si (black) in the small supercell model, where the dash and solid orange lines are the Fermi levels of IrTe2 before () and after () corrections. VBM of silicon is set to be the energy zero."

Fig 5

Calculated SBH for different TMD/Si heterojunctions. (a) Band structure of Si from HSE functional, showing a bandgap of 1.13 eV. (b–f) SBH for IrTe2/Si, NiTe2/Si, PdTe2/Si, PtTe2/Si, and ZrTe2/Si heterojunctions, respectively. The left axis represents the SBH for holes (Φp), and the right axis represents the SBH for electrons (Φn) as a function of TMD layer number."

Table 2

Schottky barrier height of electron (Φn) (eV) for heterojunctions of 2D TMD materials with varying thicknesses. Note that the monolayer PtTe2 exhibits a semiconducting phase, and hence not provided here."