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Ultrafast carrier thermalization and trapping in silicon-germanium alloy probed by extreme ultraviolet transient absorption spectroscopy

Zürch, Michael and Chang, Hung-Tzu and Kraus, Peter M. and Cushing, Scott K. and Borja, Lauren J. and Gandman, Andrey and Kaplan, Christopher J. and Oh, Myoung Hwan and Prell, James S. and Prendergast, David and Pemmaraju, Chaitanya D. and Neumark, Daniel M. and Leone, Stephen R. (2017) Ultrafast carrier thermalization and trapping in silicon-germanium alloy probed by extreme ultraviolet transient absorption spectroscopy. Structural Dynamics, 4 (4). Art. No. 044029. ISSN 2329-7778. PMCID PMC5461173. https://resolver.caltech.edu/CaltechAUTHORS:20180627-110158675

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Abstract

Semiconductor alloys containing silicon and germanium are of growing importance for compact and highly efficient photonic devices due to their favorable properties for direct integration into silicon platforms and wide tunability of optical parameters. Here, we report the simultaneous direct and energy-resolved probing of ultrafast electron and hole dynamics in a silicon-germanium alloy with the stoichiometry Si_(0.2)5Ge_(0.75) by extreme ultraviolet transient absorption spectroscopy. Probing the photoinduced dynamics of charge carriers at the germanium M_(4,5)-edge (∼30 eV) allows the germanium atoms to be used as reporter atoms for carrier dynamics in the alloy. The photoexcitation of electrons across the direct and indirect band gap into conduction band (CB) valleys and their subsequent hot carrier relaxation are observed and compared to pure germanium, where the Ge direct (ΔE_(gap,Ge,direct) = 0.8eV) and Si_(0.25)Ge_(0.75) indirect gaps (ΔE_(gap,Si_(0.25)Ge_(0.75),indirect) = 0.95 eV) are comparable in energy. In the alloy, comparable carrier lifetimes are observed for the X, L, and Γ valleys in the conduction band. A midgap feature associated with electrons accumulating in trap states near the CB edge following intraband thermalization is observed in the Si_(0.25)Ge_(0.75) alloy. The successful implementation of the reporter atom concept for capturing the dynamics of the electronic bands by site-specific probing in solids opens a route to study carrier dynamics in more complex materials with femtosecond and sub-femtosecond temporal resolution.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1063/1.4985056DOIArticle
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5461173PubMed CentralArticle
ORCID:
AuthorORCID
Cushing, Scott K.0000-0003-3538-2259
Neumark, Daniel M.0000-0002-3762-9473
Leone, Stephen R.0000-0003-1819-1338
Additional Information:© 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). (Received 21 February 2017; accepted 24 May 2017; published online 6 June 2017) M.Z. acknowledges supplementary support by the Army Research Office (ARO) (WN911NF-14-1-0383). H.-T.C. and L.J.B. acknowledge support by the Air Force Office of Scientific Research (AFOSR) (FA9550-15-1-0037). Additional funding for L.J.B. was provided by NSSEFF. Funding for C.J.K. was provided by the Defense Advanced Research Projects Agency PULSE program through Grant No. W31P4Q-13-1-0017. The initial instrument development and experimental work was supported by the Office of Assistant Secretary of Defense for Research and Engineering through a National Security Science and Engineering Faculty Fellowship (NSSEFF) and W. M. Keck Foundation. J.S.P. and A.G. acknowledge support by NSSEFF. S.K.C. acknowledges a postdoctoral fellowship through the Office of Energy Efficiency and Renewable Energy of the Department of Energy. P.M.K. acknowledges support from the Swiss National Science Foundation (P2EZP2_165252). M.Z. acknowledges support from the Humboldt Foundation. The Department of Energy under Contract No. DE-AC03-76SF00098 is acknowledged for additional experimental equipment. Theoretical work by C.D.P. and D.P. was performed as part of a User Project at The Molecular Foundry (TMF), Lawrence Berkeley National Laboratory. TMF is supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231. Portions of C.D.P.'s DFT calculations were carried out within TIMES at SLAC supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. Numerical simulations were executed on the Lawrencium computer clusters, administered by the High-Performance Computing Services Group at LBNL. We acknowledge A. Schwartzberg for help taking Raman measurements on the thin films.
Funders:
Funding AgencyGrant Number
Army Research Office (ARO)WN911NF-14-1-0383
Air Force Office of Scientific Research (AFOSR)FA9550-15-1-0037
National Security Science and Engineering Faculty FellowshipUNSPECIFIED
Defense Advanced Research Projects Agency (DARPA)W31P4Q-13-1-0017
W. M. Keck FoundationUNSPECIFIED
Swiss National Science Foundation (SNSF)P2EZP2_165252
Alexander von Humboldt FoundationUNSPECIFIED
Department of Energy (DOE)DE-AC03-76SF00098
Department of Energy (DOE)DE-AC02-05CH11231
Department of Energy (DOE)DE-AC02-76SF00515
Issue or Number:4
PubMed Central ID:PMC5461173
Record Number:CaltechAUTHORS:20180627-110158675
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180627-110158675
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87395
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:27 Jun 2018 20:42
Last Modified:03 Oct 2019 19:55

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