Effects of an external electric field on the electronic properties of MSi2PxAsy monolayers and homojunctions: a first-principles study

Abstract

Using first-principles density functional theory (DFT), we systematically investigate the influence of a perpendicular external electric field (E_ext) on the electronic properties of monolayer and homojunction structures of MSi₂P_xAs_y (M = Mo, W; x + y = 4). Our results demonstrate that an external electric field of approximately 0.7 V Å⁻¹ induces a direct-to-indirect bandgap transition, followed by a semiconductor-to-metal phase transition in the monolayer. The Rashba spin splitting around the Γ point, as captured by a derived k·p Hamiltonian, exhibits a tunable magnitude that depends linearly on the E_ext, with a maximum coefficient of 0.08 eV Å. Moreover, the E_ext leads to a significant redistribution of charge density and a rearrangement of the electronic structure, resulting in the formation of a type-II band alignment in the homojunction. These findings reveal the strongly tunable electronic and spin-dependent behavior of MSi₂P_xAs_y monolayers under external fields, suggesting their potential for application in flexible electronic, spintronic, and optoelectronic devices, particularly those utilizing field-driven transitions.