Quasi-Direct Optical Transitions in Silicon Nanocrystals with Intensity Exceeding the Bulk

Benjamin G. Lee, Jun Wei Luo, Nathan R. Neale, Matthew C. Beard, Daniel Hiller, Margit Zacharias, Paul Stradins, Alex Zunger

Research output: Contribution to journalArticlepeer-review

55 Scopus Citations

Abstract

Comparison of the measured absolute absorption cross section on a per Si atom basis of plasma-synthesized Si nanocrystals (NCs) with the absorption of bulk crystalline Si shows that while near the band edge the NC absorption is weaker than the bulk, yet above ∼2.2 eV the NC absorbs up to 5 times more than the bulk. Using atomistic screened pseudopotential calculations we show that this enhancement arises from interface-induced scattering that enhances the quasi-direct, zero-phonon transitions by mixing direct Γ-like wave function character into the indirect X-like conduction band states, as well as from space confinement that broadens the distribution of wave functions in k-space. The absorption enhancement factor increases exponentially with decreasing NC size and is correlated with the exponentially increasing direct Γ-like wave function character mixed into the NC conduction states. This observation and its theoretical understanding could lead to engineering of Si and other indirect band gap NC materials for optical and optoelectronic applications.

Original languageAmerican English
Pages (from-to)1583-1589
Number of pages7
JournalNano Letters
Volume16
Issue number3
DOIs
StatePublished - 9 Mar 2016

Bibliographical note

Publisher Copyright:
© 2016 American Chemical Society.

NREL Publication Number

  • NREL/JA-5J00-65272

Keywords

  • absorption cross section
  • atomistic screened pseudopotential
  • optical absorption
  • quantum dots
  • Silicon nanocrystals

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