Effects of an external electric field on the electronic properties of MSi(2)P(x)As(y) monolayers and homojunctions: a first-principles study.

Using first-principles density functional theory (DFT), we systematically investigate the influence of a perpendicular external electric field () on the electronic properties of monolayer and homojunction structures of MSiPAs M = Mo, W; + = 4. Our results demonstrate that an external electric field of approximately 0.7 V Å induces a direct-to-indirect bandgap transition, followed by a semiconductor-to-metal phase transition in the monolayer. The Rashba spin splitting around the point, as captured by a derived · Hamiltonian, exhibits a tunable magnitude that depends linearly on the , with a maximum coefficient of 0.08 eV Å. Moreover, the 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 MSiPAs monolayers under external fields, suggesting their potential for application in flexible electronic, spintronic, and optoelectronic devices, particularly those utilizing field-driven transitions.