Growth-Driven Polymorphism Engineering and Direct Phase Modulation of α- and β′-In2Se3

Two-dimensional (2D) In ₂ Se ₃ represents a uniquely versatile platform for novel electronics, hosting the rare coexistence of paraelectric (β), antiferroelectric (β'), and ferroelectric (α) phases. However, synthesizing phase-pure In ₂ Se ₃ films, particularly the critical ferroelectric semiconducting α-phase, is fundamentally hindered by the subtle structural distinctions and minimal energetic differences among its polymorphs. Here, we directly reveal phase-selective growth of In ₂ Se ₃ on mica using cross-sectional transmission electron microscopy (TEM). It is found that both chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques yield exclusively either the pure β′ phase or coexisting monolayer α and β′ phases, with the cooling rate playing a critical role in phase selection. Crucially, in situ stress release within the epitaxial film on mica generates wrinkles propagating along the <> direction, triggering an immediate β' to α phase transformation. The resulting phase-pure α-In ₂ Se ₃ films enable ferroelectric transistors exhibiting a high electron mobility of 259 cm ² V ^-1 s ^-1 . This precise control over polymorph synthesis unlocks promising opportunities for 2D ferroelectric devices and nanoelectronics, offering a pathway to harness phase-specific functionalities.