Group IV semiconductor nanowires

What is the difference between the skin of the Statue of Liberty in New York, and an electric wire? Both are made of the same material (copper), but they have different properties because of the shape. Now, get your shrinking machine and make your electric wire smaller than one of your hair. Do you expect the wire to keep the same properties? Nope, of course!

You can do really amazing thing just changing the shape and the size of any material. This is what I did to enable new light sources made of silicon. All our electronics devices are made of silicon. Unfortunately, it cannot emit light by itself. But, if you fabricate a silicon wire smaller than a virus, things will change.

I investigated the growth of silicon and germanium nanowires by a self-assembled method, using electron beam evaporation. This is a relatively unexploited technique that offers a pathway towards high throughput production. By properly varying the experimental parameters of the evaporation it is possible to define the length, density and crystallographic orientation of the wires. The structural properties have been correlated to the atomistic growth mechanism. Moreover, we explored the possibility to bend and restore the wires. Ion beam irradiation amorphizes the nanowires, causing their bending in the direction opposite to the beam. A full recovery is possible after thermal annealing.

I explored a top-down approach as well. Metal-Assisted Chemical Etching is a full VLSI compatible process to grow very thin nanowires of arbitrary length and controlled doping. Room-temperature photoluminescence and electroluminescence has been demonstrated from silicon nanowires. Moreover, I introduced an innovative approach, based on the combination of standard Electron Beam Lithography and reactive ion etching, for nanopatterning nanowires in any arbitrary geometry. We demonstrate broadband photoluminescence enhancement up to approximately one order of magnitude after a reliable engineering of periodic and aperiodic array patterns.

These projects have been funded partly by University of Catania and CSFNSM (Growth and characterization of Si and Ge nanowires), and performed during my PhD course.

Publication output

Book / Book chapter

Conference participation

  • E-MRS Fall Meeting 2010 – Warsaw (PL) September 13-17, 2010 Oral presentation, Symposium E
  • International School on “Materials for Renewable Energies” – Erice (TP, Italy) May 28 – June 2, 2010 Poster session
  • E-MRS 2009 – Strasbourg (F) June 8-12, 2009 Oral presentation, Symposium I
  • NODE International Summer School – Cortona (AR, Italy) July 1-5, 2008 Poster session
  • XV International Winter School on “New Developments in Solid State Physics” – Bad HofGastein (Salzburg, AT) February 18-22, 2008
  • XIII National School of Materials Science – Bressanone (Bz, Italy) September 30 – October 9, 2007 Poster session
  • XV International conference on “Ion Beam Modification of Materials” – Taormina (ME, Italy) September 18-22, 2006 Poster session

Sub-250 nm optical gain

Room temperature deep-UV optical gain has been demonstrated in AlGaN/AlN multiple quantum wells structure with strong band-structure potential fluctuations grown by Molecular Beam Epitaxy. A maximum net modal gain of 118 cm-1 has been measured and the transparency threshold of 5 µJ/cm2 was experimentally determined. Amplified Spontaneous Emission results strongly TE-polarized.

This work has been funded by DARPA – Defense Advanced Research Projects Agency CMUVT Program under subcontract from Photon Systems Inc. (2011, March – 2012, March) and performed at Boston University.

Publication output

Conference proceedings

  • Sub-250nm room temperature optical gain from AlGaN materials with strong compositional fluctuations
    E. F. Pecora, W. Zhang, H. Sun, A. Yu. Nikiforov, J. Yin, R. Paiella, T. D. Moustakas, L. Dal Negro
    Bulletin of the American Physical Society, vol. 58, V1.00111
  • Sub-250nm room temperature optical gain from AlGaN/AlN multiple quantum wells structures
    E. F. Pecora, W. Zhang, L. Zhou, D. J. Smith, J. Yin, R. Paiella, L. Dal Negro, T. D. Moustakas
    CLEO: Science and Innovations, CTh3D, CTh3D.5
  • Sub-250nm room-temperature optical gain from AlGaN/AlN multiple quantum dot structures
    E. F. Pecora, W. Zhang, L. Zhou, D. J. Smith, J. Yin, R. Paiella, L. Dal Negro, T. D. Moustakas
    Bulletin of the American Physical Society, vol. 57
  • Room temperature low threshold stimulated emission of electron beam-pumped AlGaN-based deep UV laser structures emitting below 250 nm
    A. Nikiforov, W. Zhang, J. Woodward, J. Yin, E. Pecora, L. Zhou, L. Dal Negro, R. Paiella, D. Smith, T. Moustakas, A. Moldawer
    Bulletin of the American Physical Society, vol. 57

Conference participation

  • APS March Meeting 2013 – Baltimore, MD (USA) March 18 – 22, 2013 Poster presentation, Session V1
  • CLEO Conference 2012 – San Jose, CA (USA) May 6 – 11, 2012 Oral presentation, Session “Low-dimensional Photonic Structures”
  • APS March Meeting 2012 – Boston, MA (USA) February 27 – March 2, 2012 Oral presentation, Session L28