Polymorphism and Ferroelectricity in Indium(III) Selenide

Two-dimensional indium(III) selenide (In2Se3) is characterized by rich polymorphism and offers the prospect of overcoming thickness-related depolarization effects in conventional ferroelectrics. α-In2Se3 has attracted attention as a ferroelectric semiconductor that can retain ferroelectricity at the monolayer level; thus, it can be potentially deployed in high density memory switching modes that bypasses the traditional von Neumann architecture in device design. However, studies involving α-In2Se3 are often hindered by difficulties in phase identification owing to mixing with β-In2Se3. β-In2Se3 has several polymorphs, among which include the antiferroelectric and ferroelastic β′-In2Se3. It is important to understand polymorph transitions and crystal–amorphous phase transitions in β-In2Se3 to tap into the potential of this material for resistive memory storage. In this review, we discuss how the various polymorphs and polytypes of In2Se3 can be rigorously differentiated and further highlight recent applications of these phases in ferroelectrics and memory devices.