Strain modulation in 2D GaSe epitaxial films by substrate engineering via molecular beam epitaxy (MBE)

In this work, we systematically investigate the epitaxial growth of GaSe thin films on different substrates, including GaAs(100), GaAs(111), GaN/Al₂O₃(0001), and SrTiO₃(001), using molecular beam epitaxy (MBE). All films exhibit a universal strain configuration with biaxial tensile strain in the basal plane coupled with out-of-plane compressive strain, whose magnitude varies with substrate type. On cubic GaAs substrates, GaSe grows with well-aligned single domains, while hexagonal GaN and perovskite STO promote multiple domain orientations, reflecting the role of interfacial symmetry mismatch. X-ray diffraction confirms out-of-plane lattice contraction, with compressive strain ranging from ∼1.3 % on GaAs(1 0 0) to ∼2.5 % on GaN(0001). Raman spectroscopy shows red-shifts of the in-plane $E_{2g}^2$ phonon mode, directly evidencing biaxial tensile strain. These findings demonstrate that substrate-induced strain, governed primarily by symmetry mismatch, provides a powerful and intrinsic route to tailor the optical and electronic properties of GaSe, enabling new strategies for strain-engineered 2D optoelectronic devices.