Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices

Aditya Kulkarni; Laurens D.A. Siebbeles

doi:10.1117/12.2311452

Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices

ChemE/Opto-electronic Materials

Research output: Chapter in Book/Conference proceedings/Edited volume › Conference contribution › Scientific › peer-review

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Abstract

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 language	English
Title of host publication	Proceedings of SPIE
Subtitle of host publication	Advances in Ultrafast Condensed Phase Physics
Publisher	SPIE
Number of pages	9
Volume	10673
ISBN (Electronic)	9781510618725
DOIs	https://doi.org/10.1117/12.2311452
Publication status	Published - 2018
Event	SPIE Photonics Europe 2018 - Strasbourg Convention & Exhibition Centre, Strasbourg, France Duration: 22 Apr 2018 → 26 Apr 2018 https://spie.org/conferences-and-exhibitions/photonics-europe

Conference

Conference	SPIE Photonics Europe 2018
Country/Territory	France
City	Strasbourg
Period	22/04/18 → 26/04/18
Internet address	https://spie.org/conferences-and-exhibitions/photonics-europe

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.

Keywords

carrier multiplication
charge cooling
charge generation
charge mobility
Nanocrystal

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10.1117/12.2311452

1067306taverneFinal published version, 2.26 MB

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title = "Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices",

abstract = "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.",

keywords = "carrier multiplication, charge cooling, charge generation, charge mobility, Nanocrystal",

author = "Aditya Kulkarni and Siebbeles, {Laurens D.A.}",

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volume = "10673",

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Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices. / Kulkarni, Aditya; Siebbeles, Laurens D.A.
Proceedings of SPIE: Advances in Ultrafast Condensed Phase Physics. Vol. 10673 SPIE, 2018. 1067306.

Research output: Chapter in Book/Conference proceedings/Edited volume › Conference contribution › Scientific › peer-review

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PY - 2018

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N2 - 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.

AB - 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.

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Ultrafast charge cooling and carrier multiplication in semiconductor nanocrystals and superlattices

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