First-principles investigation of the electronic, piezoelectric and transport properties of InSeX (X = Cl, Br, I) monolayers.

Abstract

First-principles calculation was performed to study InSeX (X = Cl, Br, and I) monolayers, which are formed by the breaking of In-In bonds in InSe monolayers through full halogenation. The isolated InSeX monolayers have Se-In-X stacking configuration with a buckled honeycomb structure maintained by newly formed Se-sp³ hybrid orbitals. InSeX (X = Cl, Br, and I) monolayers have good mechanical properties with Young's modulus in the range of 28.69-33.44 N m^-1 and a Poisson's ratio of nearly 0.30. Their in-plane structures are expected to be highly isotropic due to the independence of elastic parameters on the angle of applied strains. A high carrier concentration (10²⁰ cm^-3) and scattering mechanisms greatly reduce the mobility of these monolayers, especially at high temperature. However, the InSeI monolayer appears to be a promising material because its electron mobility is rather high, 10.82-217.33 cm² V^-1 s^-1, at a temperature of 50-400 K. InSeX (X = Cl, Br, and I) monolayers are also promising piezoelectric materials with high in-plane piezoelectric coefficients e ₁₁ in the range of 3.34-5.60 × 10^-10 C m^-1 and d ₁₁ of 14.90-33.50 pm V^-1. The current study provides the mechanism of how isolated InSeX (X = Cl, Br, and I) monolayers are formed and stabilized, which is useful to expand the new subclass of 2D materials by applying the same procedure for group XIII monochalcogenides (MX, where M = B, Al, Ga, In, Tl and X = S, Se, Te). InSeX (X = Cl, Br, and I) monolayers are also promising for a wide range of applications because of the broad tunability of the bandgap (1.36-2.94 eV), band edge positions, and work function (4.80-7.80 eV).