Identification of two-dimensional layered dielectrics from first principles

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.

Identification of Two-Dimensional Layered Dielectrics from First Principles

Two-dimensional (2D) van der Waals (vdW) materials promise ideal electrostatic control of charge carrier flow in a channel free of surface roughness or defects. To realize this ideal, good vdW dielectrics are needed in addition to the well explored channel materials. We study the dielectric properties of 32 easily exfoliable vdW materials using first principles methods. Specifically, we calculate the static and optical dielectric response of the monolayer and bulk form. In monolayers, we discover a strong out-of-plane response in GeClF (10.99), LaOBr (13.20), LaOCl (55.80) and PbClF (15.17), while the in-plane dielectric response is strong in BiOCl, PbClF, and TlF, ranging from 64.86 to 98.37. To assess their potential as gate dielectrics, we calculate the bandgap and electron affinity, and estimate the leakage current through the dielectric. We discover seven monolayer 2D dielectrics that promise to outperform bulk HfO2: LaOBr, LaOCl, CaHI, SrBrF, SrHBr, SrHI, and TlF with lower leakage currents at a significantly reduced 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 on vdW transistor channel materials.

Band structure of one-dimensional photonic crystal with graphene layers using the Fresnel coefficients method

In this paper, we have calculated the band structure of an instance of one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics via the Fresnel coefficients method. Then, we supposed the addition of a thin layer of graphene to each dielectric layer and the given photonic crystal (PC) composed of dielectric–graphene composites. The effects of graphene layers on the PC band structure were evaluated. We found out that according to the effective medium theory unlike the TE polarization, the electric permittivity of the dielectric layers changed at TM polarization. As such, the band structure of PC for TM polarization changed, too. Moreover, instead of bandgap related to “zero averaged refractive index” an approximately omnidirectional bandgap appeared and a related bandgap to “[Formula: see text] = 0” disappeared. In addition, a new angular gap branch appeared at a new frequency at TM polarization in which the width of gap increased as the angle increased.

Band structure of one-dimensional doped photonic crystal with three level atoms using the Fresnel coefficients method

We consider a one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics. Electric permittivity and magnetic permeability of this crystal depends on the incident electromagnetic wave frequency. We suppose that three level atoms have been added to the second layer of each dielectric and this photonic crystal (PC) has been doped. These atoms can be added to the layer with different rates. In this paper, we have calculated and compared the band structure of the mentioned PC considering the effect of added atoms to the second layer with different rates through the Fresnel coefficients method. We find out that according to the effective medium theory, the electric permittivity of the second layer changes. Also the band structure of PC for both TE and TM polarizations changes, too. The width of bandgaps related to “zero averaged refractive index” and “Bragg” increases. Moreover, new gap branches appear in new frequencies at both TE and TM polarizations. In specific state, two branches of “zero permittivity” gap appear in the PC band structure related to TM polarization. With increasing the amount of the filling rate of total volume with three level atoms, we observe a lot of changes in the PC band structure.