A Shallow Acceptor of Phosphorous Doped in MoSe2 Monolayer

Tuning the conductivity and other electronic properties by doping in ultrathin layers of transition-metal dichalcogenides is of great scientific and practical interest. As with traditional semiconductors, controllable doping is essential for device applications of the materials. Here, hole doping in epitaxial MoSe2 by phosphorus (P) are reported, where substitutional P at the Se sites acts as a shallow acceptor. P substituting Se in MoSe2 is identified by annular dark field scanning transmission electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. Scanning tunneling spectroscopy and ultraviolet photoemission spectroscopy reveal in-gap defect states and Fermi-level shifts, suggesting the hole doping effect of substitutional P. Combining with density functional theory calculation and partial charge analysis, the binding energies of impurity levels of group V elements in a MoSe2 monolayer are elucidated, where the dopant energy level becomes shallower with increasing atomic mass.