Ab-Initio Investigations into Frenkel Defects in Hexagonal Boron Nitride for Quantum Optoelectronic Applications

The van Der Waals material, hexagonal boron nitride (h-BN) is being studied extensively for electronics, sensing, photonics, and quantum technology. Identifying distinct point-defects that may be employed to create qubits and single photon emitters with specific properties has recently boosted defect engineering research in h-BN. The assignment of defects to specific characteristics of h-BN is a subject of contention and so necessitates further investigation. We have examined the defect stability under different growth conditions for the assignment of defect states for the aforementioned applications using first-principles calculations. In this work, it is found that boron Frenkel pairs (V_B-B_i) play very critical role under N-rich and N-poor growth conditions. Boron Frenkel pairs were found to activate magnetic behaviour (with 0.45 μ_B) by forming spin active defect-states in forbidden gap. Furthermore, four distinct absorption peaks in the sub-bandgap regions (with peak values at 2.47, 2.30, 1.98, and 1.61 eV) have been observed, resulting into the well-known ∼2 eV emission. The large ultraviolet quantum efficiency observed in h-BN has been explained by considering Frenkel pairs as primary defect centres, which leads to strong photocatalytic and photovoltaic properties. This work will establish Frenkel pairs as one of the most intriguing defect states in h-BN leading towards various optoelectronic and quantum applications.