Structural and optical properties of a layered ε-GaSe thin film under elastic deformation from flexible PET substrate

The present study focuses on the structural and optical characterizations of a GaSe thin-film consisting of few layers mechanically exfoliated from bulk GaSe on a flexible PET substrate. The XRD and the RAMAN spectroscopies confirm the high crystallinity of our material and show that it belongs to the hexagonal ε-GaSe polytype with a mean crystallite size of about 50 ​nm. The sample's SEM images exhibit the two-dimensional nature of the layers. The optical transmission measurements clearly show two absorbing edges. They were assigned to an indirect band gap at 1.92 ​eV and to a direct one at 2.2 ​eV. The appreciable difference between the two gaps, of about 0.28 ​eV, is attributed to a compressive biaxial strain. A value, as high as 104 ​cm−1, of the absorption coefficient has been obtained which demonstrates the GaSe material's great potential for optoelectronic applications.