Sub-10 nm High-Performance P-Type Transistors Based on Two-Dimensional HfX2 (X = Cl, Br, I): A Density Functional Theory–Nonequilibrium Green’s Function Study

As conventional Moore’s Law approaches physical scaling limits, the semiconductor industry has entered the post-Moore era, and two-dimensional (2D) semiconductors have emerged as candidate channel materials. Meanwhile, the lack of high-performance (HP) p-type field-effect transistors (FETs) hinders the development of high-efficiency complementary circuits. In this work, we systematically investigate the electronic structures and ballistic transport properties of monolayer HfX2 (X = Cl, Br, I) using first-principles calculations in combination with the nonequilibrium Green’s function (NEGF) method. The results show that 2D HfCl2, HfBr2, and HfI2 are indirect-band-gap semiconductors with band gaps of 0.85–1.03 eV and exhibit isotropy in the hole effective mass: m0 denotes the rest of a free electron. The hole effective mass is 0.30–0.38 m0 along the x and y direction. When the channel length is 5 nm, HfCl2, HfBr2, and HfI2 MOSFETs yield ballistic-performance upper-limit on-state currents Ion of 1197, 1087, and 1111 μA/μm, respectively. Moreover, HfI2 FETs with channel lengths ranging from 5 to 9 nm all meet the high-performance device requirements defined by the International Technology Roadmap for Semiconductors (ITRS). The comprehensive material performance demonstrates that monolayer HfX2 are promising p-type channel materials for next-generation high-speed and low-power 2D FETs.