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Electron and Hole Relaxation Pathways in II-VI Semiconductor Nanocrystals

Published online by Cambridge University Press:  09 August 2011

V. I. Klimov ,
Ch. Schwarz ,
X. Yang ,
D. W. McBranch ,
C. A. Leatherdale  and
M. G. Bawendi
V. I. Klimov
Affiliation:
Chemical Sciences and Technology Division, CST-6, MS-J585, Los Alamos National Laboratory, Los Alamos, NM 87545, klimov@lanl.gov
Ch. Schwarz
Affiliation:
Chemical Sciences and Technology Division, CST-6, MS-J585, Los Alamos National Laboratory, Los Alamos, NM 87545, klimov@lanl.gov
X. Yang
Affiliation:
Chemical Sciences and Technology Division, CST-6, MS-J585, Los Alamos National Laboratory, Los Alamos, NM 87545, klimov@lanl.gov
D. W. McBranch
Affiliation:
Chemical Sciences and Technology Division, CST-6, MS-J585, Los Alamos National Laboratory, Los Alamos, NM 87545, klimov@lanl.gov
C. A. Leatherdale
Affiliation:
Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
M. G. Bawendi
Affiliation:
Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
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Abstract

Femtosecond (fs) broad-band transient absorption (TA) is used to study the intra-band relaxation and depopulation dynamics of electron and hole quantized states in CdSe nanocrystals (NC's) with a range of surface properties. Instead of the drastic reduction in the energy relaxation rate expected due to a 'phonon bottleneck', we observe a fast sub-picosecond 1P-to-1S relaxation, with the rate enhanced in NC's of smaller radius. We use fs IR TA to probe electron and hole intraband transitions, which allows us to distinguish between electron and hole pathways leading to the depopulation of NC quantized states. In contrast to electron relaxation, which is controlled by NC surface passivation, depopulation of hole quantized states is extremely fast (sub-ps-to-ps time scales) in all types samples, independent of NC surface treatment (including NC's overcoated with a ZnS layer). Our results indicate that ultrafast hole dynamics are not due to trapping at surface defects, but rather arise from relaxation into intrinsic NC states.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 536: Symposium F – Microcrystalline & Nanocrystalline Semiconductors - 1998 , 1998 , 211
Copyright
Copyright © Materials Research Society 1999

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