Mechano-electronic Superlattices in Silicon Nanoribbons

Significant new mechanical and electronic phenomena can arise in single-crystal semiconductors when their thickness reaches nanometer dimensions, where the two surfaces of the crystal are physically close enough to each other that what happens at one surface influences what happens at the other. We show experimentally that, in silicon nanomembranes, through-membrane elastic interactions cause the double-sided ordering of epitaxially grown nanostressors that locally and periodically highly strains the membrane, leading to a strain lattice.  Because strain influences band structure, we create a periodic band gap modulation, up to 20% of the band gap, effectively an electronic superlattice.  Our calculations demonstrate that discrete mini-bands can be generated in the potential wells of an electronic superlattice generated by Ge nanostressors on a sufficiently thin Si(001) nanomembrane at the temperature of 77K. We predict that it is possible to observe discrete mini-bands in Si nanoribbons at room temperature if nanostressors of a different material are grown. ¬†We are currently working on the thermoelectrical, electrical and optical measurements of this unique structure.

 

Strain in Si Superlattice
Figure 1. Strain and electronic superlattices in Si nanoribbons. (a) A schematic graph of doubled-side ordering of Ge QDs grown on a 10 nm thick Si nanoribbon and the calculated strain profile shows 1D strain lattice in it. (b) A SEM image of a Si ribbon with doubled-side ordering of SiGe QDs. (c) Schematic diagrams of a 1D strain lattice and corresponding periodic-potential shapes. (d) Calculated mini-band structures for Ge QDs on Si.

 

Author: Ming Huang

References:
M. Huang et. al., ACS Nano 3, 721-727 (2009)
D. Yu et. al., Phys. Rev. B, 78,245204-1-8 (2008)