A First-Principles Study on Electronic, Thermodynamic, and Dielectric Properties of Monolayer Ca(OH)2 and Mg(OH)2

TL;DR

This study uses first-principles calculations to analyze the electronic, thermodynamic, and dielectric properties of monolayer Ca(OH)2 and Mg(OH)2, highlighting their potential as dielectric materials in 2D FETs.

Contribution

It provides detailed first-principles insights into the properties of monolayer Ca(OH)2 and Mg(OH)2, proposing their use in advanced 2D electronic devices.

Findings

Mg(OH)2 has higher out-of-plane dielectric constant than Ca(OH)2.

Bilayer Mg(OH)2 exhibits lower leakage current and EOT compared to Ca(OH)2.

Mg(OH)2 outperforms bilayer h-BN as a dielectric material.

Abstract

We perform first-principles calculations to explore electronic, thermodynamic, and dielectric properties of two-dimensional (2D) layered, alkaline-earth hydroxides Ca(OH)2 and Mg(OH)2. We calculate the lattice parameters, exfoliation energies, and phonon spectra of monolayers and also investigate the thermal properties of these monolayers such as Helmholtz free energy, heat capacity at constant volume, and entropy as a function of temperature. We employ Density Functional Perturbation Theory (DFPT) to calculate the in-plane and out-of-plane static dielectric constant of the bulk and monolayer samples. We compute the bandgap and electron affinity values using the HSE06 functional and estimate the leakage current density of transistors with monolayer Ca(OH)2 and Mg(OH)2 as dielectrics when combined with HfS2 and WS2, respectively. Our results show that bilayer Mg(OH)2 (EOT ~ 0.60 nm) with a lower solubility in water, offers higher out-of-plane dielectric constants and lower leakage currents than bilayer Ca(OH)2 (EOT ~ 0.56 nm). Additionally, the out-of-plane dielectric constant, leakage current, and EOT of Mg(OH)2 outperform bilayer h-BN. We verify the applicability of Anderson's rule and conclude that bilayers of Ca(OH)2 and Mg(OH)2 respectively paired with lattice-matched monolayer HfS2 and WS2 are effective structural combinations that could lead to the development of innovative multi-functional Field Effect Transistors (FETs).