Spontaneous polarization induced photocurrent mechanisms in 3R-MoS2-graphene heterostructures

Rohmbohedrally stacked transition metal dichalcogenides (TMD) exhibit broken inversion symmetry and have been shown to be ferroelectric up to room temperature. When sandwiched between two graphene electrodes, the 3R-MoS2 develops a large depolarization field, which leads to a significant photovoltaic (PV) effect. On the other hand, the spontaneous polarization also induces image charges in top and bottom graphene electrodes, resulting in a chemical potential imbalance and a corresponding photo-thermoelectric (PTE) effect. These two photocurrents both occur at zero bias and therefore are difficult to distinguish in the steady state measurement. Here we perform the ultrafast photocurrent autocorrelation experiment in 3R-MoS2-graphene devices. We find the autocorrelation response of the PV and PTE effects are opposite in direction and have different time scales, which are limited by cooling of the lattice and electron, respectively. These results reveal the intrinsic mechanisms behind the spontaneous photocurrent in 3R-MoS2 devices and can help further optimize ferroelectric TMD heterostructures for practical optoelectronic applications.