To realize effective van der Waals (vdW) transistors, vdW dielectrics are needed in addition to vdW channel materials. We study the dielectric properties of 32 exfoliable vdW materials using first principles methods. We calculate the static and optical dielectric constants and discover a large out-of-plane permittivity in GeClF, PbClF, LaOBr, and LaOCl, while the in-plane permittivity is high in BiOCl, PbClF, and TlF. To assess their potential as gate dielectrics, we calculate the band gap and electron affinity, and estimate the leakage current through the candidate dielectrics. We discover six monolayer dielectrics that promise to outperform bulk HfO2: HoOI, LaOBr, LaOCl, LaOI, SrI2, and YOBr with low leakage current and low equivalent oxide thickness. Of these, LaOBr and LaOCl are the most promising and our findings motivate the growth and exfoliation of rare-earth oxyhalides for their use as vdW dielectrics.
Using first-principles calculations, we investigate six transition-metal nitride halides as potential vdW dielectrics for transition metal dichalcogenide channel transistors. We identify the best combinations for the p-MOS transistor technology.
We perform first-principles calculations to explore the 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 the 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 does 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).
Recent
developments in the field of two-dimensional (2D) van der
Waals (vdW) dielectrics have captured great interest because of potential
applications of 2D materials in future generations of complementary
metal-oxide semiconductor (CMOS) technologies. In this Spotlight article,
we highlight the progress we recently made toward the discovery of
2D vdW dielectrics, which will be critical to realizing a vdW transistor
technology. We provide an overview of how to calculate the dielectric
properties of 2D vdW dielectric candidates from first-principles using
density functional theory. Furthermore, we show how to quantify the
anticipated leakage current through a 2D vdW dielectric. We illustrate
the use of hexagonal boron nitride (h-BN), oxyhalides, transition-metal
nitride halides (TMNH), and alkaline hydroxides.
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