Multiple Quantum Well Structures of Graphene Nanoribbons

Graphene is a new two dimensonal atomically thin form of carbon in honeycomb crystal structure. It has recently been isolated from graphite (which was was  thought to be impossible for a long time). Graphene has lots of unique properties and offers extraordinary applications for future's nanotechnology. It is extensively studied throughout the world. Graphene nanoribbons are  geometrically terminated forms of perfect 2D graphene, where the charge carriers are confined in two dimension and free to move in third direction. They are particularly important due to their well defined geometry and possible ease of manipulation. Graphene nanoribbons can be characterized according to their edge shape, i.e. armchair or zigzag. Based on first-principles calculations we predict that periodically repeated junctions of armchair graphene nanoribbons of different widths form multiple quantum well structures. In these superlattice heterostructures the width as well as the energy-band gap is modulated in real space and specific states are confined in certain segments. Not only the size modulation, but also composition modulation, such as periodically repeated and commensurate heterojunctions of boron nitride and graphene honeycomb nanoribbons, results in a multiple quantum well structure. The geometrical features of the constituent nanoribbons, namely, their widths and lengths, the form of the junction, as well as the symmetry of the resulting superlattice, are the structural parameters available to engineer electronic properties of these quantum structures. We present our analysis regarding the variation of the band gaps and the confined states with these structural parameters. Calculation of transmission coefficient through a double barrier resonant tunneling device formed from a finite segment of such a multiple quantum well structure and placed between metallic electrodes yields resonant peaks which can be identified with electronic states confined in the well. We show that these graphene-based quantum structures can introduce interesting concepts to design nanodevices.

H. Sevinçli, M. Topsakal, and S. Ciraci
PHYSICAL REVIEW B 78 , 245402  (2008)
Editorially selected  for IOP www.nanotechweb.org  Technology Update