Ultrathin two-dimensional van der Waals asymmetric ferroelectric semiconductor junctions

Two-dimensional van der Waals ferroelectric semiconductors have attracted extensive research interest in both theoretical investigation and device applications due to their ferroelectricity and semiconducting nature. However, it is still not well understood how the ferroelectric phase is able to coexist with the semiconducting phase in this emerging material class. In this work, mm-scale continuous films of In₂Se₃ with a thickness of ∼3 nm were synthesized successfully by physical vapor deposition. Furthermore, we fabricated asymmetric ferroelectric semiconductor junctions (a-FSJs) from thick exfoliated and PVD-grown ultrathin In₂Se₃ films. A high read current density of ∼100 A/cm² and a distinction ratio of over 10² at V_Read= 0.5 V are achieved in devices fabricated by a 3 nm-thick In₂Se₃ film toward ultrahigh-density memory integration. Notably, the coercive voltage is constant, with In₂Se₃ film thickness decreasing from 200 to 3 nm. A qualitative model is proposed to elucidate the anomalous film-thickness-independent coercive voltage in this ultrathin a-FSJ, which can also be generalized to other emerging two-dimensional ferroelectric semiconductors.