Carbon annealed HPHT-hexagonal boron nitride: Exploring defect levels using 2D materials combined through van der Waals interface

Hexagonal boron nitride (h-BN) is a layered material that is generating interest in various fields owing to its fascinating properties. We present a multi-stranded analysis of carbon defects in h-BN using intentionally carbon (C)-doped h-BN crystals. Carbon defects were introduced into h-BN crystals synthesized under high-pressure and high-temperature (HPHT) conditions by a process of carbon annealing. We employ an innovative approach to explore impurity states in our C-doped h-BN by assembling it into van der Waals heterostructures with other 2D materials. Attaching graphene as a probe material to determine the impurity states in the h-BN bandgap, we locate an acceptor state above the Dirac point of graphene on C-doped h-BN, which causes anomalous bending in the Landau fan diagram. Furthermore, we adopt tungsten disulfide (WS₂) as another probe material and assess the influence of C-doped h-BN on the emission spectrum of the WS₂ monolayers. Our work reveals the nature of the carbon impurities in h-BN and also uncovers their effects on adjacent 2D materials.