Dear friend Subham Mahanti

Not all 2D materials have zero band gaps at certain points in their Brillouin zone, like graphene. The electronic properties of a 2D material depend on its crystal structure, symmetry, and chemical composition, among other factors.

Graphene has a zero band gap due to its unique honeycomb lattice structure and the overlap of its two sublattices. On the other hand, hBN has a wide band gap of ~6 eV because of the difference in electronegativity between boron and nitrogen atoms, which leads to a large charge transfer and a significant energy difference between the valence and conduction bands.

In general, the electronic properties of 2D materials can be tailored by controlling their composition, crystal structure, and doping. Some 2D materials may have a nonzero band gap in their pristine form, while others can be engineered to have a band gap or even exhibit exotic electronic properties such as topological insulators or Dirac materials.

References:

1. Novoselov, K. S., et al. "Two-dimensional atomic crystals." Proceedings of the National Academy of Sciences 102.30 (2005): 10451-10453.

2. Watanabe, Kenji, et al. "Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal." Nature materials 3.6 (2004): 404-409.

3. Castro Neto, A. H., et al. "The electronic properties of graphene." Reviews of modern physics 81.1 (2009): 109.