Simulation of Z-Shaped Graphene Geometric Diodes Using Particle-in-Cell Monte Carlo Method in the Quasi-Ballistic Regime.

John Stearns,Garret Moddel

doi:10.3390/nano11092361

Abstract

Geometric diodes are planar conductors patterned asymmetrically to provide electrical asymmetry, and they have exhibited high-frequency rectification in infrared rectennas. These devices function by ballistic or quasi-ballistic transport in which the transport characteristics are sensitive to the device geometry. Common methods for predicting device performance rely on the assumption of totally ballistic transport and neglect the effects of electron momentum relaxation. We present a particle-in-cell Monte Carlo simulation method that allows the prediction of the current–voltage characteristics of geometric diodes operating quasi-ballistically, with the mean-free-path length shorter than the critical device dimensions. With this simulation method, we analyze a new diode geometry made from graphene that shows an improvement in rectification capability over previous geometries. We find that the current rectification capability of a given geometry is optimized for a specific mean-free-path length, such that arbitrarily large mean-free-path lengths are not desirable. These results present a new avenue for understanding geometric effects in the quasi-ballistic regime and show that the relationship between device dimensions and the carrier mean-free-path length can be adjusted to optimize device performance.

Highlights

We defined geometric diodes as planar conductors patterned with a geometric asymmetry that gives rise to a preferred current direction in 2008 [1], and we have demonstrated that they rectify at DC and infrared frequencies [2,3]
These times are sampled from an exponential decay distribution where e−t/τ represents the probability that an electron picked at random will have no collision during the time interval t, and τ = λMFP/vF represents the average momentum relaxation time of the choice material [15]
MFP of λpeak is likely to change based on the applied voltage the resulting asymmetry was calculated, with the results shown in shape, and it may not exist at all for certain geometries

Summary

Introduction

We defined geometric diodes as planar conductors patterned with a geometric asymmetry that gives rise to a preferred current direction in 2008 [1], and we have demonstrated that they rectify at DC and infrared frequencies [2,3] Since these diodes are planar and have extremely low capacitance, they have the potential to provide ultra-fast rectification. For a geometric diode to exhibit rectification, charge carriers must travel ballistically (λMFP greater than device dimensions) or quasi-ballistically (λMFP near device dimensions) through the patterned material, which requires that device dimensions be on the order of λMFP or lower This imposes difficult fabrication requirements for devices made of conventional metals, as typical mean-free-path lengths are below 100 nm. Such graphene devices have been demonstrated experimentally [2,3,8] and are capable of infrared rectification

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Discussion

Conclusion