Effect of stacking order and in-plane strain on the electronic properties of bilayer GeSe.

Germanium selenide as a new layered material is promising for nanoelectronic applications due to its unique optoelectronic properties and tunable band gap. In this study, based on density functional theory, we systematically investigated the structure, stability, and electronic properties of bilayer germanium selenide with four different stacking orders (namely AA-, AB-, AC- and AD-stacking). The obtained results indicated that the band gap is dependent on the stacking order with an indirect band gap for AA- and AC-stacking and direct band gap for AB- and AD-stacking. In addition, we also found that the band gap of the GeSe bilayer with different stacking orders can be tuned by in-plane strain. The transition between the direct to indirect band gap or semiconductor to metal is tunable. In particular, the direct band gap of the AB-stacking germanium selenide bilayer can be tuned in a wide energy range under applied strain along the armchair direction.