December 2, 2011Ph.D. Thesis Presentation First principles simulations of nanoelectronic devices Jesse Maassen (Supervisor : Prof. Hong Guo) Department of Physics, McGill University, Montreal, QC Canada

December 2, 2011Ph.D. Thesis Presentation Why first principles theory? Line of ~ 50 atoms nm YearChannel length nm nm ? (Source: ITRS 2010)

December 2, 2011Ph.D. Thesis Presentation Why first principles theory? ScienceEngineering Atomic structure : surfaces, chemical bonding, interfaces, dissimilar materials, charge transfer, roughness, variability, … tunneling, conductance quantization, spin-transport, … Quantum effects : First principles

December 2, 2011Ph.D. Thesis Presentation How to calculate transport properties? Taylor et al., PRB 63, (2001) Waldron et al., PRL 97, (2006) Maassen et al., IEEE (submitted)

December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen et al., Appl. Phys. Lett. 97, (2010); Maassen et al., Nano. Lett. 11,151 (2011)

December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen and Guo, preprint to be submitted

December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen et al., PRB 80, (2009)

December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen et al., PRB 80, (2009)

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Motivation :  Graphene has interesting properties (i.e., 2D material, zero gap, linear dispersion bands, …).  For electronics, all graphene sheets must be contacted via metal electrodes (source/drain).  How does the graphene/metal interface affect the response of a device?  Theoretical studies exclude accurate treatment of electrodes.

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Transport properties :

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Atomic structure :  Cu, Ni and Co (111) have in-place lattice constants that almost match that of graphene.  Equilibrium interface structure determined from atomic relaxations. Metal eq Maassen et al., Appl. Phys. Lett. 97, (2010); Maassen et al., Nano. Lett. 11,151 (2011)

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact :  Linear dispersion bands near Fermi level.  Zero band gap.  States only in the vicinity of K.

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact :  Strong hybridization with metal  Band gap opening  Graphene is spin-polarized Maassen et al., Nano. Lett. 11, 151 (2011) : Top-site C(p z ) : Hollow-site C(p z ) : Ni(d Z 2 )

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact : Maassen et al., Nano. Lett. 11, 151 (2011)

December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact : Maassen et al., Nano. Lett. 11, 151 (2011)

December 2, 2011Ph.D. Thesis Presentation CHANNEL Application : Localized doping in Si nano-transistors Motivation :  Leakage current accounts for 60% of energy in transistors.  Two sources : (i) gate tunneling and (ii) source/drain tunneling.  How can highly controlled doping profiles affect leakage current ?

December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  Structure: n-p-n and p-n-p.  Channel doping: B or P.  L = 6.5 nm  15.2 nm  Si band gap = 1.11 eV Technical details regarding random doping, large-scale modeling and predicting accurate semiconductor band gaps can be found in the thesis.

December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  G MAX / G MIN ~ 50.  Lowest G with doping in the middle of the channel. Maassen and Guo, preprint to be submitted

December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors Maassen and Guo, preprint to be submitted

December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors Maassen and Guo, preprint to be submitted

December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  G decreases with L.  Variations in G increase dramatically with L. Maassen and Guo, preprint to be submitted

December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  G decreases with L.  Variations in G increase dramatically with L. Maassen and Guo, preprint to be submitted

December 2, 2011Ph.D. Thesis Presentation Summary  First principles transport theory is a valuable tool for quantitative predictions of nanoelectronics, where atomic/quantum effects are important.  I determined that the effect of metallic contacts (Cu, Ni, Co) can significantly influence device characteristics. I found that the atomic structure of the graphene/metal interface is crucial for a accurate treatment.  My simulations on localized doping profiles demonstrated how leakage current can be substantially reduced in addition to alleviating device variations.

December 2, 2011Ph.D. Thesis Presentation Thank you! Questions ?