Polymorphism and Ferroelectricity in Indium(III) Selenide.

Two-dimensional indium(III) selenide (InSe) is characterized by rich polymorphism and offers the prospect of overcoming thickness-related depolarization effects in conventional ferroelectrics. α-InSe 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-InSe are often hindered by difficulties in phase identification owing to mixing with β-InSe. β-InSe has several polymorphs, among which include the antiferroelectric and ferroelastic β'-InSe. It is important to understand polymorph transitions and crystal-amorphous phase transitions in β-InSe to tap into the potential of this material for resistive memory storage. In this review, we discuss how the various polymorphs and polytypes of InSe can be rigorously differentiated and further highlight recent applications of these phases in ferroelectrics and memory devices.