1. Bent Weber 1, S. Mahapatra 1,2, W, Clarke 1, M. Y. Simmons 1,2 1) School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia 2) Australian Research Counsel Centre of Excellence for Quantum Computer Technology, Sydney, Australia H. Ryu, S. Lee, G. Klimeck Network for Computational Nanotechnology, Purdue University, West Lafayette, IN 47907, USA L. C. L. Hollenberg Center for Quantum Computer Technology, School of Physics, University of Melbourne, VIC 3010, Australia

2. Applications of Silicon Nanowires In-plane gates / leads for silicon donor-based quantum computing Silicon nanowire transistors Fuhrer et al., NanoLetters 9 (2), 707 (2009) Fuechsle et al., Nat. Nanotech., advance online publication (2010) Singh et al., IEEE Electron Device Letters 27 (5), 383 (2006) Cui et al., NanoLetters 3 (2), 149 (2003)

3. As the diameter reaches the nano-scale:  Surface scattering (< 4 nm)  Carrier depletion due to surface/interface states  Doping challenging  Limited to (~ 10 20 cm -3 ) (VLS)  Dopant-segregation (< 5 nm)  Quantum confinement (<10 nm)  Dielectric confinement (<30 nm) Limits of Conduction in Nanowires Electron beam lithography, RIE etching STM-lithography, δ-doping and molecular beam epitaxy STM-lithography, δ-doping and molecular beam epitaxy 1.7 nm 25 nm STM-fabricated wires:  Elimination of surface effects  High doping levels (~ 10 21 cm -3 )  Full dopant activation Vaurette et al., J. Vac. Sci. Technol. B 26 (3), 945 (2008)

4. Atomic-Precision Doping by STM Si 4 nm H2H2 STM-tip STM hydrogen lithography SDBSDB H:SiH:Si STM- patterned ~25nm epitaxial encapsulation (~250°C) ~25nm epitaxial encapsulation (~250°C) Al contacts UHV

5. Ohmic Conductors at the Atomic Scale Ruess et al. Nanotechnology 18, 044023 (2007)

6. ¼ ML planar coverage N D,2D = 2.4 x 10 14 cm -2 d < 1 nm N D,3D = ~ 10 21 cm -3 >> N Mott ~ 3 x 10 18 cm -3 Atomistic Modeling of Si Nanowires T = 4K Electronic structure modeling with atomistic representation, using NEMO-3D d lith =1.7 nm d leff =3.4 nm A eff

7. Diameter-Independent Resistivity 9x10 18 3x10 19 1.5x10 20

8. Conclusions  Narrowest doped silicon nanowires, showing Ohmic conduction  Diameter-independent resistivity, comparable to bulk value  full dopant activation down to ~2 nm  Atomistic tight-binding calculations (NEMO-3D) to compute electronic structure

9. Thanks to …  Dr. A. Fuhrer (now IBM Rueschlikon, Switzerland) and Dr. T.C.G. Reusch (now OSRAM Opto Semiconductors, Regensburg, Germany)  The UNSW Quantum Electronic Devices group of Prof. A. R. Hamilton (especially Dr. T. Martin, Dr. O. Klochan, A/Prof A. P. Micolich)  This work was supported by the Australian Research Council, the Army Research Office under contract number W911NF-08-1-0527 and the National Science Foundation (NSF). Computational resources on nanoHUB.org, NICS, TACC, and Oak Ridge National Lab were utilized.