Impacts of h-BN Stacking Sequence and Layer Thickness on the Band Structure and Radiative Recombination*

We investigated the variation of the electronic and optical properties of h-BN as a function of stacking sequence and number of layers using first-principles calculations. Our study includes bulk and bilayer structures for the five possible stacking sequences, as well as monolayer and randomly stacked bulk structures (t-BN). Variations of the band structure were studied both at the density functional theory (DFT) and GW levels, with particular focus on the band extrema. The majority of the investigated structures were found to have indirect band gaps, with a few exceptions such as the AB₁ stacking sequence and t-BN. We further calculated the phonon-assisted optical matrix elements (S) for all structures to understand how the number of layers and stacking type influence light emission. Most of the ordered bulk and bilayer structures are capable of efficient light emission with values of S² ranging from ~10-1000× that of bulk Si, indicating that efficient phonon-assisted light emission is possible even though the gap is indirect.