Modification of the Band Gap of Hexagonal Boron Nitride in Contact with Graphene Through Systematic Annealing

Graphene/hexagonal boron nitride heterostructures provides an effective platform for tuning graphene’s electronic and optical properties while preserving its inherently high carrier mobility. In this work, the effect of post-growth thermal annealing on the optical band gap of G/h-BN heterostructures is investigated to examine temperature-dependent modifications at the graphene–substrate interface. The optical response of the annealed heterostructures was characterized using UV–Vis spectroscopy over the spectral range of 200–800 nm. The absorption spectra reveal a systematic red shift of the absorption edge with increasing annealing temperature, indicating a progressive modification of the electronic structure. Tauc method was used in the approximation of the optical band gap where a reduction of the optical band gap from 2.86 eV for the lower annealing temperature to 2.17 eV at the highest annealing temperature was observed. This act is associated to thermally induced interfacial relaxation, including changes in stacking configuration, and moirés super lattice formation. These processes lead to a reduction in substrate-induced symmetry breaking in graphene, thereby influencing its optical transitions. The findings contribute to a better understanding of temperature-driven interfacial effects in van der Waals heterostructures and provide insights relevant to the development of graphene-based optoelectronic and thermoelectric devices designed to operate under varying thermal conditions.