Effects of artificial stacking configurations and biaxial strain on the structural, electronic and transport properties of bilayer GaSe- A first principle study

The Gallium Selenide (GaSe) is one of the emerging members in the two-dimensional (2D) semiconductor family and being actively explored for electronic and optoelectronic applications. However, to this date, systematic theoretical investigations are yet to be observed on simultaneous effects of interlayer stacking arrangements and applied biaxial strains in few-layer GaSe for realizing tunable electronic and transport properties. In this work, the bilayer (2L) GaSe is considered in its natural as well as three energetically stable artificial interlayer stacking arrangements and is subjected to biaxial compressive and tensile strains. The subsequent modulations in the structural, electronic, and transport properties are systematically analysed from the in-plane, and inter-plane electronic redistributions using density functional theory (DFT) based first principle calculations. In this context, emphasis has been given to the energy bandgaps and effective masses of 2L-GaSe. The results indicate that strain and artificial stacking together can lead to significant changes in the in-plane and interlayer electronic distributions and, thereby, the electronic band structures and transmission spectrum of 2L-GaSe. The applied biaxial compressive strain appears highly effective for linearly tuning the bandgap and effective masses with noticeably different values for different stacking arrangements. Interestingly, under applied biaxial tensile strain, highly nonlinear variations in energy bandgap and effective mass are observed along with characteristic shifts in the position of conduction band minima (CBM) and Valence Band Maxima (VBM) for different stacking orientations. The key findings of this work offer detailed theoretical and design-level insight for strain/stacking co-optimization strategy in 2L-GaSe for realizing high-performance electronic and optoelectronic devices.