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Femtosecond tracking of carrier relaxation in germanium with extreme ultraviolet transient reflectivity

Kaplan, Christopher J. and Kraus, Peter M. and Ross, Andrew D. and Zürch, Michael and Cushing, Scott K. and Jager, Marieke F. and Chang, Hung-Tzu and Gullikson, Eric M. and Neumark, Daniel M. and Leone, Stephen R. (2018) Femtosecond tracking of carrier relaxation in germanium with extreme ultraviolet transient reflectivity. Physical Review B, 97 (20). Art. No. 205202. ISSN 2469-9950. doi:10.1103/PhysRevB.97.205202.

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Extreme ultraviolet (XUV) transient reflectivity around the germanium M_(4,5) edge (3d core-level to valence transition) at 30 eV is advanced to obtain the transient dielectric function of crystalline germanium [100] on femtosecond to picosecond time scales following photoexcitation by broadband visible-to-infrared (VIS/NIR) pulses. By fitting the transient dielectric function, carrier-phonon induced relaxations are extracted for the excited carrier distribution. The measurements reveal a hot electron relaxation rate of 3.2 ± 0.2 ps attributed to the X−L intervalley scattering and a hot hole relaxation rate of 600 ± 300 fs ascribed to intravalley scattering within the heavy hole (HH) band, both in good agreement with previous work. An overall energy shift of the XUV dielectric function is assigned to a thermally induced band gap shrinkage by formation of acoustic phonons, which is observed to be on a timescale of 4–5 ps, in agreement with previously measured optical phonon lifetimes. The results reveal that the transient reflectivity signal at an angle of 66° with respect to the surface normal is dominated by changes to the real part of the dielectric function, due to the near critical angle of incidence of the experiment (66°–70°) for the range of XUV energies used. This work provides a methodology for interpreting XUV transient reflectivity near core-level transitions, and it demonstrates the power of the XUV spectral region for measuring ultrafast excitation dynamics in solids.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kaplan, Christopher J.0000-0002-5873-9487
Cushing, Scott K.0000-0003-3538-2259
Chang, Hung-Tzu0000-0001-7378-8212
Neumark, Daniel M.0000-0002-3762-9473
Leone, Stephen R.0000-0003-1819-1338
Additional Information:© 2018 American Physical Society. (Received 21 February 2018; published 8 May 2018) C.J.K. acknowledges support by the Defense Advanced Research Projects Agency PULSE program through grant W31P4Q-13-1-0017. P.M.K. acknowledges support from the Swiss National Science Foundation (Grant Nos. P2EZP2_165252 and P300P2_174293). M.Z. acknowledges support by the Army Research Office (ARO) (WN911NF-14-1-0383). S.K.C. acknowledges a postdoctoral fellowship through the Office of Energy Efficiency and Renewable Energy of the Department of Energy M.Z. acknowledges support from the Humboldt Foundation. H.-T.C. acknowledges support by the Air Force Office of Scientific Research (AFOSR) (FA9550-15-1-0037). 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. C.J.K. and P.M.K. each contributed equally to this work.
Funding AgencyGrant Number
Defense Advanced Research Projects Agency (DARPA)W31P4Q-13-1-0017
Swiss National Science Foundation (SNSF)P2EZP2_165252
Swiss National Science Foundation (SNSF)P300P2_174293
Army Research Office (ARO)WN911NF-14-1-0383
Department of Energy (DOE)UNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
Air Force Office of Scientific Research (AFOSR)FA9550-15-1-0037
National Security Science and Engineering Faculty FellowshipUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Issue or Number:20
Record Number:CaltechAUTHORS:20180627-095819556
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87382
Deposited By: George Porter
Deposited On:27 Jun 2018 17:14
Last Modified:15 Nov 2021 20:47

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