Charge percolation pathways guided by defects in quantum dot solids

Yingjie Zhang, Danylo Zherebetskyy, Noah D. Bronstein, Sara Barja, Leonid Lichtenstein, David Schuppisser, Lin Wang Wang, A. Paul Alivisatos, Miquel Salmeron

Research output: Contribution to journalArticlepeer-review


Charge hopping and percolation in quantum dot (QD) solids has been widely studied, but the microscopic nature of the percolation process is not understood or determined. Here we present the first imaging of the charge percolation pathways in two-dimensional PbS QD arrays using Kelvin probe force microscopy (KPFM). We show that under dark conditions electrons percolate via in-gap states (IGS) instead of the conduction band, while holes percolate via valence band states. This novel transport behavior is explained by the electronic structure and energy level alignment of the individual QDs, which was measured by scanning tunneling spectroscopy (STS). Chemical treatments with hydrazine can remove the IGS, resulting in an intrinsic defect-free semiconductor, as revealed by STS and surface potential spectroscopy. The control over IGS can guide the design of novel electronic devices with impurity conduction, and photodiodes with controlled doping.

Original languageEnglish (US)
Pages (from-to)3249-3253
Number of pages5
JournalNano letters
Issue number5
StatePublished - May 13 2015
Externally publishedYes


  • Kelvin probe force microscopy
  • Quantum dot
  • charge percolation
  • charge transport
  • defect
  • in-gap states

ASJC Scopus subject areas

  • Bioengineering
  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanical Engineering


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