Photogalvanic effect in monolayer WSe2-MoS2 lateral heterojunction from first principles

Abstract

Abstract Density functional theory calculations and non-equilibrium Green's function method are carried out to study the photovoltaic effect of monolayer WSe2-MoS2 lateral heterojunction under vertical irradiation. We report the photoresponse behavior under different polarized lights and photon energies combined with charge density difference, electronic structure, and the joint density states under illumination. According to the charge density difference, the electrons transfer from MoS2 to WSe2 before illumination, but here generates the photocurrent under the vertical illumination due to the broken spatial inversion asymmetry of the device. Remarkably, the photocurrent increases from zero then decreases, and finally a reverse breakdown occurs. The photocurrent increases from zero since the electrons will be excited from the valence band to the conduction band only if the photon energy is greater than the energy gap of heterojunction material. As the illumination energy increases, the concentration difference of the excited electrons first increases and then decreases, leading to the photocurrent first increases and then decreases. Finally, the current reverses and suddenly increases because the Zener breakdown occurs. Furthermore, the photoresponse of system for linearly polarized light is similar with that for elliptically polarized light. This work demonstrates the basic principle of photovoltaic effect of single-layer WSe2-MoS2 lateral heterojunction, which can be further applied for novel electronic and optoelectronic devices based on quantum confined 2D lateral heterostructures.