Density Functional Theory and Modelling of Electronic and Magnetic Properties of 2D Hexagonal Boron Nitride Doped with IVA-Group Elements

Hexagonal boron nitride (h-BN) is a 2D material with unique properties including a wide bandgap, high thermal conductivity, chemical stability, and simple chemical stoichiometry. These characteristics make h-BN attractive for device applications in electronics, spintronics, and optoelectronics. h-BN films allow for defect states to act as coherent quantum emitters in 610-642 nm wavelength range with relatively long lifetimes and photostability. Due to the wide band gap, room temperature emission becomes feasible. However, different defect such as boron or nitrogen single, pair or triple defect types alter the crystal stability, crystal symmetry, electronic band structure, magnetic order, phonon density of states, emission characteristics, and Raman spectra. Because different defect types may form at the same time in chemical vapor deposition, exfoliation or even molecular beam epitaxy, a detailed understanding of the defect types and their corresponding characteristic signatures such as crystal stability and symmetry, electronic band structure, Fermi level tuning, density of states and Raman spectra is needed. To elucidate these signatures and to tailor h-BN for applications, we used density functional theory (DFT) to identify defect type (vacancy, dopant IVA element type), configuration, and concentration dependence of h-BN structural stability, electronic band structure and magnetic moments.

In 2D materials, substitutional doping during growth can be used to alter the electronic and magnetic properties in advanced technologies such as spintronics and optoelectronics. Here, we report the effects of doping IVA-group elements (C, Si, Ge, Sn, Pb) into 2D hexagonal boron nitride (h-BN) based on first-principles density functional theory (DFT) calculations. Doping was performed at boron sites for n-type doping and nitrogen sites for p-type doping at various concentrations from 3.125% to 9.375%. Pristine h-BN is a semiconductor with a large bandgap (~4.67 eV) and exhibits non-magnetic behavior. However, 3.125% doping with IVA-group elements can effectively reduce the bandgap (0.39 ~ 0.56 eV) and introducing new defect bands, while maintaining their semiconductor properties. Increasing the doping concentration to 6.25% causes the magnetization to vanish with both n-type doping (C and Si) and p-type doping (C and Ge) due to the strong ionic interactions of dopants. Interestingly, the magnetization becomes stronger upon increasing the doping level 9.375% with a total magnetic moment of up to 2.26 μB with Ge and 1.54 μB with Si impurities. This doping level also results in the material exhibiting half-metallicity. The presence of half- metallicity can be explained based on the unpaired electron in the 2p orbital of doping IVA-group atoms. Additionally, configurations for doping were examined to ascertain doping site importance.

This comprehensive investigation highlights the significant potential of defect engineering in 2D materials, offering a pathway to customize h-BN for specific technological applications. This comprehensive investigation highlights the significant potential of defect engineering in 2D materials, offering a pathway to customize h-BN for specific technological applications. By systematically doping h-BN with IVA-group elements, we have demonstrated the ability to modulate its electronic and magnetic properties, achieving desirable characteristics such as bandgap reduction, introduction of defect bands, and even half-metallicity at higher doping concentrations. These findings provide crucial insights into how substitutional doping can be strategically employed to enhance the performance of h-BN in advanced spintronics and optoelectronics applications. Future research should focus on further refining these doping techniques and exploring other elemental substitutions to fully exploit the unique properties of h-BN for next-generation device applications.