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Title: Electron and hole relaxation pathways in semiconductor quantum dots

Abstract

Femtosecond (fs) broad-band transient absorption (TA) is used to study the intraband relaxation and depopulation dynamics of electron and hole quantized states in CdSe nanocrystals (NC{close_quote}s) with a range of surface properties. Instead of the drastic reduction in the energy relaxation rate expected due to a {open_quotes}phonon bottleneck,{close_quotes} we observe a fast subpicosecond 1P-to-1S electron relaxation, with the rate exceeding that due to phonon emission in bulk semiconductors. The energy relaxation is enhanced with reducing the NC{close_quote}s radius, and does not show any dependence on the NC surface properties (quality of the surface passivation). These data indicate that electron energy relaxation occurs by neither multiphonon emission nor by coupling to surface defects, but is likely meditated by Auger-type electron-hole energy transfer. We use fs infrared TA to probe electron and hole intraband transitions, which allows us to distinguish between electron and hole relaxation pathways leading to the depopulation of NC quantized states. In contrast to the electron relaxation, which is controlled by NC surface passivation, the depopulation of hole quantized states is extremely fast (sub-ps-to-ps time scales) in all types of samples, independent of NC surface treatment (including NC{close_quote}s overcoated with a ZnS layer). Our results indicate that ultrafast holemore » dynamics are not due to trapping at localized surface defects such as a vacancy, but rather arise from relaxation into intrinsic NC states or intrinsically unpassivated interface states. {copyright} {ital 1999} {ital The American Physical Society}« less

Authors:
;  [1]; ;  [2]
  1. Chemical Sciences and Technology Division, CST-6, MS-J585, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
  2. Department of Chemistry and Center for Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States)
Publication Date:
OSTI Identifier:
690748
Resource Type:
Journal Article
Journal Name:
Physical Review, B: Condensed Matter
Additional Journal Information:
Journal Volume: 60; Journal Issue: 19; Other Information: PBD: Nov 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CADMIUM COMPOUNDS; CADMIUM SELENIDES; SEMICONDUCTOR DEVICES; QUANTIZATION; RELAXATION TIME; ABSORPTION SPECTRA; ENERGY-LEVEL DENSITY; RECOMBINATION; PHONONS

Citation Formats

Klimov, V I, McBranch, D W, Leatherdale, C A, and Bawendi, M G. Electron and hole relaxation pathways in semiconductor quantum dots. United States: N. p., 1999. Web. doi:10.1103/PhysRevB.60.13740.
Klimov, V I, McBranch, D W, Leatherdale, C A, & Bawendi, M G. Electron and hole relaxation pathways in semiconductor quantum dots. United States. https://doi.org/10.1103/PhysRevB.60.13740
Klimov, V I, McBranch, D W, Leatherdale, C A, and Bawendi, M G. 1999. "Electron and hole relaxation pathways in semiconductor quantum dots". United States. https://doi.org/10.1103/PhysRevB.60.13740.
@article{osti_690748,
title = {Electron and hole relaxation pathways in semiconductor quantum dots},
author = {Klimov, V I and McBranch, D W and Leatherdale, C A and Bawendi, M G},
abstractNote = {Femtosecond (fs) broad-band transient absorption (TA) is used to study the intraband relaxation and depopulation dynamics of electron and hole quantized states in CdSe nanocrystals (NC{close_quote}s) with a range of surface properties. Instead of the drastic reduction in the energy relaxation rate expected due to a {open_quotes}phonon bottleneck,{close_quotes} we observe a fast subpicosecond 1P-to-1S electron relaxation, with the rate exceeding that due to phonon emission in bulk semiconductors. The energy relaxation is enhanced with reducing the NC{close_quote}s radius, and does not show any dependence on the NC surface properties (quality of the surface passivation). These data indicate that electron energy relaxation occurs by neither multiphonon emission nor by coupling to surface defects, but is likely meditated by Auger-type electron-hole energy transfer. We use fs infrared TA to probe electron and hole intraband transitions, which allows us to distinguish between electron and hole relaxation pathways leading to the depopulation of NC quantized states. In contrast to the electron relaxation, which is controlled by NC surface passivation, the depopulation of hole quantized states is extremely fast (sub-ps-to-ps time scales) in all types of samples, independent of NC surface treatment (including NC{close_quote}s overcoated with a ZnS layer). Our results indicate that ultrafast hole dynamics are not due to trapping at localized surface defects such as a vacancy, but rather arise from relaxation into intrinsic NC states or intrinsically unpassivated interface states. {copyright} {ital 1999} {ital The American Physical Society}},
doi = {10.1103/PhysRevB.60.13740},
url = {https://www.osti.gov/biblio/690748}, journal = {Physical Review, B: Condensed Matter},
number = 19,
volume = 60,
place = {United States},
year = {1999},
month = {11}
}