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 e₁₁ in the range of 3.34–5.60 × 10⁻¹⁰ C m⁻¹ and d₁₁ 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).