Design of Tunneling diodes with 2D Insulators for Switching at THz and Beyond

The key components of a conventional rectifying circuit are semiconductor PN junction diodes. The electron transfers across a PN junction via diffusion with a typical time interval of 1-100ns. It is applicable for processing the signal at radio frequencies. However, for the signal processing at THz and higher, the time interval for electron to transmit across a junction must be faster than 1ps which can be overcome by tunneling. Metal/insulator/metal (MIM) junction is a simple and yet very effective structure for a tunneling diode. The tunneling time is defined by barrier profile U_x and bias, reaching femtosecond.

The conventional MIM diodes use bulk materials as the insulators in which the thickness cannot be fine-tuned and the surface defects negatively affect tunneling efficiency. In this work, we applied density function theory (DFT) method to study MIM junctions with two-dimensional (2D) materials as the insulators. We have studied the band structures of 1-3 layers of TiO₂, TaO₂ and SnO₂ which can be obtained by oxidizing the corresponding 2D metal-sulfur materials. The Au/monolayer TiO₂/Al junction was found to have the best rectifying performance. There is not a significant effect for up to ±0.6% of strain. In addition, the simulated current-voltage characteristics were fed through a rectifier in Pspice which showed excellent signal rectifying for frequencies at THz and beyond. Such a diode is very attractive for THz medical devices and rectenna solar cells.