Excitons under strain: light absorption and emission in strained hexagonal boron nitride

Abstract

Hexagonal boron nitride is an indirect band gap material with a strong luminescence in the ultraviolet. This luminescence originates from bound excitons recombination assisted by different phonon modes. The coupling between excitons and phonons is so strong that the resulting light emission is as efficient as the one of direct band gap materials. In this manuscript we investigate how uniaxial strain modifies the electronic and optical properties of this material, and in particular how it affects the exciton-phonon coupling. Using a formulation of this coupling based on finite-difference displacements, recently developed by some of us, we investigate how phonon-assisted transitions change under strain. Our results open the way to the study of phonon-assisted luminescence in strained materials from first principles. Our findings are important both for experiments that directly probe h-BN under strain or for those in which it is used as substrate for other 2D material with a lattice mismatch.

Interlayer and Intralayer Excitons in AlN/WS2 Heterostructure

“…This means that the variation of the lattice constant induces a change in the gap larger than the one due to AlN layer screening. The small strain applied has then essentially no effect on the excitonic binding energy, as is consistent with other works [ 59 ]. To summarize, this explains why the fully relaxed heterostructure has a larger GW gap than the isolated , even in the presence of a larger screening.…”

Pressure dependence of electronic, vibrational and optical properties of wurtzite-boron nitride

“…Moreover, in the displaced supercells we do not recalculate the dielectric constant but we use the equilibrium one. This approximation allows us to speed up calculation and it has been shown not to produce any visible error in the final luminescence spectrum [39].…”