Negative differential resistance with ultra-high peak-to-valley current ratio intunnel diodes based on two-dimensional cold metals: Vertical NbTe₂/BN/NbTe₂ heterojunction diode

The negative differential resistance (NDR) effect is of great interest for future memory and logic circuit applications. We propose a novel semiconductor-free NDR tunnel diode concept with ultra-high peak-to-valley current ratio (PVCR) [1]. Our proposed NDR diode consists of two cold metal (CM) electrodes separated by a thin insulating tunnel barrier. The NDR effect stems from the unique electronic band structure of the CM electrodes, i.e., the width of the isolated metallic bands around the Fermi level as well as the energy gaps separating higher and lower lying bands determine the current-voltage characteristics and PVCR  value of the tunnel diode. By proper choice of the CM electrodes the PVCR values as high as 10⁹ can be obtained. We employ the nonequilibrium Green's function method combined with density functional theory to demonstrate the NDR characteristics of the proposed diode based on two-dimensional CM NbTe₂ and hexagonal BN (NbTe₂/BN/NbTe₂) vertical heterojunctions.