The role of interfacial (intrinsic) electric field on the structural, electronic, linear and nonlinear optical properties of MoS2/MoSSe vdWHs

Many studies report that second harmonic generation (SHG) would be significantly modified by the interfacial electric field (interfacial-EF) in two-dimensional (2D) van der Waals heterojunctions (vdWHs). However, the physical picture between the interfacial-EF and the SHG-coefficient of 2D vdWHs has not been visualized. Hence, this manuscript studies the SHG property of 2D MoS₂/MoSSe vdWHs using first-principles calculations, focusing on the intrinsic electric field (intrinsic-EF) reversal of the MoSSe layer, expecting to amplify the interfacial-EF alternation and the SHG-coefficient alternation simultaneously. The electronic and linear optical properties, closely correlated with SHG application, are also investigated. After the intrinsic-EF reversal of the MoSSe layer, (1) larger charge transfers and stronger interfacial-EFs between the MoS₂ and MoSSe layers are obtained; (2) The linear optical absorption and the linear optical refractive index of MoS₂/MoSSe vdWHs are nearly not changed, which is confirmed by the vanishing optical transition between the MoS₂ and MoSSe layers; (3) Large out-of-plane SHG-coefficients in 2D MoS₂/MoSSe vdWHs can be induced, which is clarified by the interfacial-EF; (4) As a result, the SHG-intensity parallel to the pump field could be strengthened. Summarily, this manuscript visualizes that the SHG-coefficient and the SHG-intensity of 2D vdWHs could be enhanced by the interfacial-EF.