Polarizability of Multi-layer GaSe and Its Heterostructures: A Theoretical Study

The nonlinear optical (NLO) properties of two-dimensional materials present promising opportunities for advanced photonic and optoelectronic applications. In this work, the NLO response of multilayer gallium selenide (GaSe) was systematically investigated using periodic and finite-cluster models within the density functional theory (DFT) framework. The results show consistent layer-dependent NLO response, with odd-numbered GaSe layers exhibiting significantly larger first hyperpolarizability (β) values than their even-layer counterparts. Modifications in the NLO response due to substrates, such as graphene, h-BN monolayer, and Ag(111), were also investigated. While graphene and h-BN only slightly modify the β value relative to the pristine monolayer, the Ag(111) substrate dominates the overall NLO response. These findings provide essential guidelines for the design of GaSe-based NLO devices.