Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices

Aditya Kulkarni, Laurens D.A. Siebbeles

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

7 Downloads (Pure)


We studied charge carrier photogeneration, cooling, carrier multiplication (CM) and charge mobility and decay in: a) isolated PbSe nanocrystals in solution, b) films of PbSe nanocrystals coupled by organic ligands, and c) 2D percolative networks of epitaxially connected PbSe nanocrystals. The studies were performed using ultrafast pump-probe spectroscopy with optical or terahertz/microwave conductivity detection. The effects of electronic coupling between the nanocrystals on charge mobility were characterized by frequency-resolved microwave and terahertz photoconductivity measurements. Reducing the size of ligand molecules between nanocrystals in a film strongly increases the charge mobility. Direct connection of nanocrystals in a percolative network yielded a sum of electron and hole mobilities as high as 270±10 cm2V-1s-1. We found that a high mobility is essential for multiple electron-hole pairs formed via CM to escape from recombination. The coupling between the nanocrystals was found to strongly affect the competition between cooling of hot charges by phonon emission and CM. In percolative networks of connected nanocrystals CM is much more efficient than in films with ligands between the nanocrystals. In the e networks CM occurs in a step-like fashion with threshold near the minimum photon energy of twice the band gap.

Original languageEnglish
Title of host publicationProceedings of SPIE
Subtitle of host publicationAdvances in Ultrafast Condensed Phase Physics
Number of pages9
ISBN (Electronic)9781510618725
Publication statusPublished - 2018
EventSPIE Photonics Europe 2018 - Strasbourg Convention & Exhibition Centre, Strasbourg, France
Duration: 22 Apr 201826 Apr 2018


ConferenceSPIE Photonics Europe 2018
Internet address

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • carrier multiplication
  • charge cooling
  • charge generation
  • charge mobility
  • Nanocrystal


Dive into the research topics of 'Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices'. Together they form a unique fingerprint.

Cite this