Figure 2

Modification of the BN bandgap. (a) The gap enhancement depends mainly on λ , is weakly dependent on Δ and shows almost no change with Ω. Calculations are made for Δ =t corresponding to a BN gap of 2Δ =4.66 eV, Δ =1.20t (2Δ =5.6 eV), and Δ =0.84t (2Δ =3.92 eV, the tight binding fit from reference [10]). t =2.33 eV, $\hslash \mathrm{\Omega }=0.01t=23$ meV, $\hslash \mathrm{\Omega }=0.03t=70$ meV, $\hslash \mathrm{\Omega }=0.06t=140$ meV, $\hslash \mathrm{\Omega }=0.09t=210$ meV, covering the full range of phonon frequencies in reference [13].k _B T =0.01t (T =268K) and λ ≤1. (b) Variation of the gap with temperature, $\hslash \mathrm{\Omega }=0.05t=117$ meV and λ =0.2. There is a weak temperature dependence due to the large Δ, consistent with the measurements in reference [15], with gap starting to close only for extremely high temperatures T >8,000 K , presumably above the melting point of the material. Red circles show the size of the gap, red lines are a guide to the eye.