Unraveling In-Plane Crystallographic Anisotropy-Dependent Memory Performance In Van Der Waals α-In2Se3 Ferroelectric Semiconductor Field-Effect Transistors.

The ferroelectric semiconductor field-effect transistors (FeS-FETs) based on α-In2Se3 emerge as promising non-volatile memory devices. However, the intrinsic in-plane (IP) crystallographic anisotropy of α-In2Se3 introduces orientation dependence, leading to pronounced variations in memory performance depending on the IP alignment of the source/drain (S/D) contacts. This study presents the first demonstration of IP anisotropy-dependent ferroelectricity in α-In2Se3 FeS-FETs with S/D contacts aligned along the armchair (AC) and zigzag (ZZ) directions. The AC-aligned S/D configuration achieves a ferroelectric resistance switching (FRS) ratio of 6.42, an on/off current ratio of 4.53 × 104, and a normalized memory window (MW) of 59 %, whereas the ZZ-aligned counterpart exhibits an FRS ratio of 1.05, an on/off ratio of 5.25, and negligible MW. The electron transports proceed through twisted pathways along the AC direction, but proceed along a straight trajectory in the ZZ direction to avoid high-energy barrier regions due to the threefold rotational symmetric lattice. Thus, the excessive electron transmission and a reduced Schottky barrier height effectively screen the influence of ferroelectric bound charges in the ZZ-aligned S/D contacts. These findings establish clear correlations between IP anisotropy and the ferroelectric functionality of α-In2Se3, offering critical guidelines for the design of FeS-FETs.