University of California, Riverside

Department of Electrical and Computer Engineering



Electronic and Magneto-electronic Properties of Nanopatterned


Electronic and Magneto-electronic Properties of Nanopatterned
 
EE

Electronic and Magneto-electronic Properties of Nanopatterned

November 22, 2013 - 11:00 am
Winston Chung Hall, 205/206

Abstract:

 

Effective use of graphene in digital applications is limited due to its lack of an energy gap in its electronic spectra. We explore the possibility of any band gap tenability in graphene based structures. An atomistic model based on the Extended Huckel Theory (EHT) coupled with non-equilibrium Greens function (NEGF) formalism is used for simulating the transport characteristics. Our calculation shows that bandgap can be induced in all proposed structures and current voltage     (I − V ) characteristics mimic the characteristics of resonant tunneling diode featuring negative differential resistance (NDR). However obtaining a modest bandgap in grapheme often came at the expense of strongly degraded electron mobility with lithographic difficulties. We propose an unconventional biasing approach of modulating I − V  

characteristics without inducing any bandgap and observe NDR effect in single layer and bi-layer Graphene field-effect transistors (GFETs). Our atomistic modeling shows that the NDR appears not only in the drift-diffusion regime but also in the ballistic regime at the nanometer-scale although the physics changes. The NDR observed under certain biasing schemes is an intrinsic property of graphene resulting from its symmetric band structure. The obtained results present a conceptual change in graphene research and indicate an alternative route for graphenes applications in information processing.

 

Experimentally, the layers of bilayer or multilayer graphene tend to be misoriented with respect to each other. The        coherent, interlayer transmission (T(E)) of  misoriented bilayer graphene ribbons is a strong function of the Fermi energy and magnetic field. We investigate the magnetic field and interlayer bias dependency on transport properties of large scale misoriented bilayer graphene nanoribbon (mBGNR) heterostructure. Our simulation shows that edge states can result in a large peak in T(E) at the charge neutrality point that is several orders of magnitude larger than the surrounding low-energy transmission. The calculated coherent interlayer conductance is consistently asymmetric around the charge neutrality point for all structures with the value differing by up to 3 orders of magnitude at   Ef = ±0.05 eV. The low-energy states exhibit a high magnetoconductance (MC) ratio that tends to increase as the width of the ribbons decrease. The maximum value for the 35 nm wide bilayer ribbons at 10T is 15,000%. Non-equilibrium Green’s function calculations of T(E) are also supported by semi-analytical calculations based on Fermi’s Golden Rule. We also study interlayer bias dependency on simulated T(E). The nature of the bias modulated T(E) gives rise to non-linear current-voltage characteristics. This could be promising for potential electronic applications such as low power rectifier, switch etc.

 

More in Defenses

More Information 

General Campus Information

University of California, Riverside
900 University Ave.
Riverside, CA 92521
Tel: (951) 827-1012

Department Information

Electrical and Computer Engineering
Suite 343 Winston Chung Hall
University of California, Riverside
Riverside, CA 92521-0429

Tel: (951) 827-2484
Fax: (951) 827-2425
E-mail: E-mail/Questions

Footer