A study of alloyed nanowires from two perspectives: Approximate dispersion and transmission

Gerhard Klimeck, Purdue University
Timothy Boykin, Department of Electrical and Computer Engineering, University of Alabama
Mathieu Luisieir, Integrated Systems Laboratory
Neerav Kharche, Birck Nanotechnology Center and Purdue University
Andreas Schenk, Integrated Systems Laboratory

Abstract

Local atomic arrangement in hetero structures or disorder due to alloying, surface roughness and impurities strongly influence the bandstructure and charge transport. With decreasing diameters down to nanometer scales, disorder can no longer be treated in an average manner using the virtual crystal approximation (VCA) and the need for atomistic simulations arises. This work looks at the nanoscale devices from two different perspectives. The materials science perspective in which average bandstructure of the whole nanowire is computed using the nanoelectronic modeling tool (NEMO-3D) and the zone-unfolding algorithm. The device physics perspective, where the transmission coefficient is calculated with an atomistic non-equilibrium Green's function (N-EGF) approach. Both approaches use 20 band sp(3)d(5)s* empirical tight-binding model with spin orbit coupling. The connection between dispersions and transmission coefficients of AlGaAs random alloy nanowires is highlighted. Both, transmission coefficients and average bandstructures show reduced bandgaps and noisy behavior. Their complimentary and mutually supporting nature provides a significant insight into the physics of charge transport through disordered systems.