First-Principles Design of 3d Transition-Metal-Doped GaP Nanosheets for Multifunctional Spintronic and Optoelectronic Devices

Spin-resolved first-principles calculations show that substitutional incorporation of 3d transition metals provides a powerful way to reconfigure the properties of a GaP monolayer. In contrast to pristine GaP, which is a nonmagnetic indirect-gap semiconductor, the V-, Cr-, Mn-, Fe-, Co-, and Cu-doped systems develop localized d-derived states and pronounced spin asymmetry. The Mn-doped sheet exhibits the highest magnetic moment, reaching 5.58 μB at 6.25% concentration. Cr, Co, and Cu induce half-metallic behavior, whereas V, Mn, and Fe preserve semiconducting character with unequal gaps in the two spin channels. These results highlight transition-metal doping as an efficient route for tailoring monolayer GaP toward spintronic and visible-to-near-infrared optoelectronic applications.