The doping effects of monolayer Ca<sub>2</sub>N on electronic states: A first-principles calculation

<p indent="0mm">Given the importance of two-dimensional (2D) materials in the development of microelectronic devices, condensed matter physics and chemistry concepts, the existence of electrodes with two-dimensional electronic structures has become a hot research direction. Two-dimensional calcium nitride (Ca₂N) with a layered structure is a new type of 2D electrode materials, the conduction electrons are confined between Ca layers, and the 2D confined electrons behave as anions, showing the unique topological characteristics of electrode materials, which has potential applications in high-performance electronic devices and chemical synthesis. The space group of Ca₂N belongs to <italic>R3m</italic>, and the layers are stacked along the direction of the <italic>c</italic> axis. The interaction between the layers is through the van der Waals force, and the weak molecular force between the layers makes the single layer Ca₂N easy to be stripped from the body phase like graphene. But the influence of its electrical properties and its changing rules are not sufficiently studied. Doping can effectively regulate the electronic band structure and improve the integration of thin-layer two-dimensional materials, so as to accurately control and optimize various properties of materials. What’s more, doping not only regulates the band structure of the system, but also affects the magnetic properties of the system. It provides a novel approach for designing and constructing high-performance microelectronic devices. Therefore, the electrical properties of pure Ca₂N and the regulation of doping on its electrical properties are studied by first principles calculation based on density functional theory. Calculations were conducted using the Vienna Ab-initio Simulation Package (VASP). The energy cutoff for the plane wave basis set was set to <sc>500 eV,</sc> and the interactions between ionic cores and valence electrons were described using the projector augmented wave (PAW) method. For the exchange-correlation functional, the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional was employed. The effects of doping elements (B/C/O/F) on Ca₂N geometry and electronic structures, including atomic spacing, bond length and charge transfer, were investigated. The study reveals that the phonon spectrum of pristine two-dimensional Ca₂N shows no imaginary frequencies, indicating its thermodynamic stability. Similarly, after doping, the phonon spectra still exhibit no imaginary frequencies; however, bond distortions occur near the dopant atoms, altering the surface structure and significantly affecting the work function and electronic states. It is found that the Ca-N bond length of the nearest and second nearest neighbors is affected after all doping atoms replace N. Specifically, when B (boron) replaces N (nitrogen), the bond length between Ca and B is the longest, while the next-nearest Ca-N bond length significantly decreases. When B and C (carbon) are doped, there is a notable change in the charge distribution, which not only effectively alters the electronic states and magnetism of Ca₂N but also imparts semi-metallic characteristics. In contrast, F (fluorine) and O (oxygen) doping have a relatively minor impact on the electronic states of the system. Therefore, the appropriate selection of doping elements provides a guide for the functional chemically reactive monolayer Ca₂N electrode, so as to achieve a wide range of practical applications.