Ferroelectricity in the polytypes of In2Se3 grown by molecular beam epitaxy

Ferroelectric transition metal chalcogenides (TMC) have been used for the development of ferroelectric semiconductor field effect transistor (FeSmFET), a novel microelectronic device for which the conduction channel rather than the gate dielectric in the FET is a ferroelectric. Among polytypes of In₂Se₃, the α- and β-phases of In₂Se₃ featuring band gap values being 1. 39 and 1.41, respectively, were reported to be ferroelectric. Another polytype within the In₂Se₃ family, γ-In₂Se₃, whose structure features a polar C₆ point group, is also a promising candidate for ferroelectric semiconductor with a large bandgap of 2.1 eV, substantially larger than those of α- and β-In₂Se₃, making it potentially a channel material for FeSmFET applications as well. However, the evidence for ferroelectricity in γ-In₂Se₃ is so far limited to that obtained from piezoelectric force microscopy (PFM) measurements. We report low-temperature growth of various polytypes of In₂Se₃ on Si and SiO₂ substrates by molecular beam epitaxy (MBE) as well as their structural and electrical characterizations. In particular, we performed c-axis electrical measurements and observed hysteresis loops in the polarization and current-voltage characteristics in capacitors involving γ-In₂Se₃, suggesting that this polytype of In2Se3 is indeed ferroelectric.