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.