Doping-Modulated Semiconductor-to-Metal Transformation in a Low-Band-Gap Two-Dimensional Material

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are promising materials for next-generation complementary metal-oxide-semiconductor (CMOS) technologies owing to their atomically thin channels and strong electrostatic control. Achieving the modulation of carrier polarity within a single material system is desirable for CMOS integration but remains challenging. Low-bandgap TMDCs could facilitate effective polarity tuning. Additionally, such materials provide a sensitive medium for probing doping-induced electronic evolution, where small perturbations can strongly shift the Fermi level. Here, we employ five-layer PtSe₂, an air-stable TMDC with a low bandgap of ∼0.1 eV, as a material platform to investigate doping-driven transport modulation. Through dilute (∼2%) incorporation of period-four transition metal dopants, we drive a continuous transition from intrinsic n-type semiconducting behavior (pristine) to p-type semiconducting (V, Mn-doped), through a heavily p-doped regime (Fe-doped), and ultimately to a fully metallic state (Cr-doped). In Cr-PtSe₂, we observe four-terminal (4T) resistivity as low as 200 Ω and achieve a very high hole carrier density of ∼7.8 × 10¹⁴ cm^-2, reflecting the strong dopant-induced Fermi level tuning. This study shows a broad, doping-controlled conduction spectrum within a single TMDC, characterizes dopant-host interactions and electronic structure modulation, and is relevant to CMOS-compatible low-bandgap 2D semiconductors.