Defect and Doping Properties of Two-Dimensional PdSe₂

In this work, the defect and doping properties of monolayer (ML) PdSe₂ were investigated from first-principles calculations. The calculated formation energies of the intrinsic defects indicate that the dominant defects are adatoms, followed by antisites, and then vacancies. The charge transition levels of the intrinsic defects are extremely deep. Although the screening of the substrate can shallow the defect levels, this effect is rather weak even though the substrate has a large dielectric constant. Therefore, the unintentional doping concentration in a ML PdSe₂ is expected to be very low. Tuning the carrier density in a ML PdSe₂ through substitutional doping is difficult since the calculated ionization energies of various dopants are quite large. Alternatively, good doping behaviors in a ML PdSe₂ can be achieved through a modulation doping approach, in which the dopant is incorporated into an encapsulation CaF₂ layer that forms a heterostructure with the PdSe₂. It is shown that K and Al dopings in the CaF₂ layer introduce holes and electrons in the PdSe₂ layer, respectively, through the charge transfer driven by the type-I band alignment and large band offsets. In addition, the spatial separation of the charge carrier and the impurity significantly reduces Coulomb scattering; thus, good transport properties can be expected. These findings can be helpful for the defect control and performance optimization of 2D PdSe₂-based devices.