Crystallization-Route-Dependent Lattice Ordering and Polar Response in Layered α-In2Se3

Abstract

Vapor-phase crystallization provides an effective strategy for regulating lattice ordering and polar response in layered chalcogenide crystals. Herein, layered α-In2Se3 is used as a model polar semiconductor to clarify how open-flow chemical vapor deposition (CVD) and sealed-ampule chemical vapor transport (CVT) influence the morphology, stoichiometric retention, layered periodicity, local lattice ordering, and switchable out-of-plane polar response. CVD directly yields ultrathin substrate-supported α-In2Se3 nanosheets, but the nonequilibrium growth environment leads to a slightly In-rich composition, weaker basal diffraction, less resolved Raman features, and more pronounced local lattice-contrast fluctuations. In contrast, iodine-assisted CVT produces mechanically exfoliable multilayer α-In2Se3 crystals with composition closer to nominal stoichiometry, stronger layered periodicity, clearer vibrational fingerprints, more regular In–Se chemical-state characteristics, and improved local lattice coherence. These crystallization-induced structural advantages enable a clearer out-of-plane polar response, as evidenced by butterfly-like PFM amplitude behavior, nearly 180° phase switching, and electrically written domain contrast. A proof-of-concept α-In2Se3/InSe heterojunction further demonstrates polarization-associated interfacial transport modulation, linking crystallization-selected lattice ordering with functional polar chalcogenide interfaces.