Enhancement of monolayer SnSe light absorption by strain engineering: A DFT calculation

Strain effects on the electronic and optical properties of monolayer SnSe is studied by APW + lo method in DFT framework. The applied strains cause direct-indirect transition of SnSe band gap which is mainly constructed by s/p hybridization. The armchair epsilon(ac) and zigzag epsilon(zz) reduce the unstrained band gap of 1.05 eV down to 0 eV at 12% compression, but at 12% tension, the band gap decreases to 0.726-0.804 eV. The band gap always increases under biaxial strain epsilon(b) at 12% compression to 12% tension. We observe an enhancement of real epsilon(1) (omega) and imaginary epsilon(2) (omega) parts of dielectric function by 14%-30% of magnitude, wider peak distribution to infrared and ultra-violet regions, and appearance of new peaks in the epsilon(1) (omega) and epsilon(2) (omega) spectrums. As a consequence, the light absorption alpha(omega) is significantly enhanced in the ultra-violet region and the absorption even starts at lower energy at infrared region.