Intentional defect creation and doping in boron nitride (BN) are critical strategies for tailoring its electronic, optical, and magnetic properties. BN, a wide bandgap material, exhibits exceptional thermal stability, mechanical strength, and chemical inertness. However, its insulating nature limits direct applications in electronics and optoelectronics. To overcome this, researchers employ defect engineering and doping to introduce controlled modifications that enhance functionality.

Defect engineering in BN primarily involves creating vacancies, antisites, or interstitial defects. Nitrogen vacancies (V_N) and boron vacancies (V_B) are among the most studied defects. V_N defects introduce unoccupied states near the conduction band, while V_B defects create occupied states near the valence band. These defects can be generated via ion implantation, plasma treatment, or irradiation. For example, argon ion bombardment at energies between 50 keV and 200 keV induces V_N defects, which have been observed to increase n-type conductivity. Similarly, electron irradiation at doses exceeding 10^18 e/cm² produces V_B defects, leading to p-type behavior in hexagonal BN (hBN).

Chemical doping is another effective approach to modify BN properties. Carbon is a common dopant due to its proximity to boron and nitrogen in the periodic table. Substitutional carbon doping at nitrogen sites (C_N) introduces donor levels, while carbon at boron sites (C_B) creates acceptor levels. Studies show that C_N doping reduces the bandgap by approximately 0.5 eV, enhancing visible light absorption. Oxygen doping, achieved through annealing in oxygen-rich environments, introduces deep levels that influence photoluminescence spectra, with emission peaks shifting toward the red region.

Transition metal doping is explored for introducing magnetic properties into BN. Manganese (Mn) and iron (Fe) are notable dopants. Mn-doped BN exhibits ferromagnetic ordering at room temperature when the doping concentration exceeds 5 atomic percent. Fe doping, on the other hand, leads to antiferromagnetic coupling at low concentrations but transitions to ferromagnetism at higher doping levels (above 8 atomic percent). These modifications are achieved using techniques like co-sputtering or chemical vapor deposition with metal-organic precursors.

Ion implantation is a precise method for defect and dopant incorporation. For instance, silicon implantation into hBN at fluences of 10^14 to 10^15 ions/cm² introduces Si_N defects, which act as deep donors. Post-implantation annealing at temperatures above 800°C activates these dopants, improving carrier mobility. Similarly, magnesium implantation followed by annealing at 1000°C results in Mg_B acceptors, enabling p-type conductivity with hole concentrations up to 10^17 cm^-3.

Plasma treatment offers a less invasive alternative for defect creation. Nitrogen plasma exposure generates N vacancies, while boron plasma introduces B vacancies. The defect density can be controlled by varying plasma power and exposure time. For example, 100 W nitrogen plasma for 10 minutes produces a V_N density of 10^12 cm^-2, as confirmed by X-ray photoelectron spectroscopy (XPS).

Defect complexes, such as V_N-V_B divacancies, exhibit unique properties. These complexes introduce mid-gap states that can trap excitons, leading to prolonged photoluminescence lifetimes. The formation of such complexes is favored under high-energy particle irradiation, with divacancy concentrations reaching 10^19 cm^-3 in some cases.

Doping and defect engineering also influence optical properties. For instance, fluorine doping via reactive ion etching introduces F_B defects, which quench intrinsic UV emission and enhance defect-related visible emission. This is attributed to the formation of new electronic states within the bandgap. Similarly, sulfur doping during growth creates S_N defects, leading to broad emission bands centered at 550 nm.

Magnetic property modulation is achievable through defect engineering. Neutron irradiation induces spin-polarized defects in BN, resulting in room-temperature ferromagnetism with a saturation magnetization of 0.1 emu/g. This is linked to the formation of defect-induced magnetic moments. Additionally, cobalt doping via ion implantation produces Co_B defects, which exhibit a magnetic anisotropy energy of 1 meV per atom.

The choice of technique depends on the desired property modification. Ion implantation offers depth control but requires annealing for dopant activation. Chemical doping during growth provides uniform distribution but may introduce unintended impurities. Plasma treatment is suitable for surface modifications but lacks depth precision. Each method has trade-offs in terms of defect density, spatial resolution, and thermal budget.

Challenges remain in achieving high dopant activation rates and minimizing compensating defects. For example, excessive nitrogen vacancy creation can lead to charge trapping, degrading device performance. Advanced characterization techniques like deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR) are essential for quantifying defect states and their impact on material properties.

Future directions include exploring co-doping strategies to balance charge carriers and investigating new dopants like rare earth elements for optoelectronic applications. The integration of defect-engineered BN with other 2D materials also presents opportunities for heterostructure devices with tailored functionalities.

In summary, intentional defect creation and doping in BN enable precise control over its electronic, optical, and magnetic properties. Techniques such as ion implantation, chemical doping, and plasma treatment provide versatile pathways for property modification, paving the way for advanced applications in electronics, photonics, and spintronics. Continued advancements in defect engineering will further expand the utility of BN in emerging technologies.