Band Gap Engineering of Hexagonal SnSe Nanostructured Thin Films for Infra-Red Photodetection.

We, for the first time, provide the experimental demonstration on the band gap engineering of layered hexagonal SnSe nanostructured thin films by varying the thickness. For 50 nm thick film, the band gap is ~2.04 eV similar to that of monolayer, whereas the band gap is approximately ~1.2 eV similar to that of bulk for the 1200 nm thick film. The variation of the band gap is consistent with the the theoretically predicted layer-dependent band gap of SnSe. Interestingly, the 400-1200 nm thick films were sensitiveto 1064 nm laser iradiation and the sensitivity increases almost exponentiallly with thickness, while films with 50-140 nm thick are insensitive which is due to the fact that the band gap of thinner films is greater than the energy corresponding to 1064 nm. Over all, our results establish the possibility of engineering the band gap of SnSe layered structures by simply controlling the thickness of the film to absorb a wide range of electromagnetic radiation from infra-red to visible range.