Doping-tunable charge ordering in semiconducting single-layer Cr₂Se₃

The charge density wave (CDW), a charge ordering phase, offers a valuable framework for exploring electron-electron interactions, electron-phonon coupling, and quantum phase transitions. In CDW materials, carrier density substantially influences the ground state, typically altered through foreign ion doping and investigated at macro- or mesoscopic scales via photoemission or transport techniques. However, atomic-scale visualization, particularly in doped CDW systems without foreign ions, remains rare. Here, we present real-space observation of doping-tunable granular charge ordering using scanning tunneling microscopy (STM) in semiconducting single-layer Cr₂Se₃, a group VIB transition metal chalcogenide (TMC). Observations of lattice distortion, bandgap modulation at E_F, and STM contrast inversion at low temperatures indicate a charge ordering origin. Cr₂Se₃'s semiconducting nature enables charge ordering modulation through doping: Hole doping suppresses it, whereas electron doping alters the pattern, yielding a periodic 3√3 × 3√3 CDW phase. This tunable charge ordering in a group VIB TMC advances the understanding of charge doping and ordering interactions in two-dimensional materials.