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

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 0.25Ge 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 = 0.8 eV) and Si 0.25Ge 0.75 indirect gaps (ΔE gap,Si0.25Ge0.75,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 0.25Ge 0.75 alloy. The successful implementation of the reporter atom conceptmore » 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.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
  2. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). The Molecular Foundry
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). The Molecular Foundry; SLAC National Accelerator Lab., Menlo Park, CA (United States). Theory Inst. for Materials and Energy Spectroscopies
  5. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
  6. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry. Dept. of Physics; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
Publication Date:
Grant/Contract Number:
AC02-05CH11231; AC03-76SF00098; AC02-76SF00515; WN911NF-14-1-0383; FA9550-15-1-0037; W31P4Q-13-1-0017; P2EZP2_165252
Type:
Accepted Manuscript
Journal Name:
Structural Dynamics
Additional Journal Information:
Journal Volume: 4; Journal Issue: 4; Journal ID: ISSN 2329-7778
Publisher:
American Crystallographic Association/AIP
Research Org:
Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Energy Efficiency and Renewable Energy (EERE); US Army Research Office (ARO); US Air Force Office of Scientific Research (AFOSR); Defense Advanced Research Projects Agency (DARPA) (United States); USDOD; W. M. Keck Foundation (United States); Swiss National Science Foundation (SNSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; germanium; elemental semiconductors; band gap; conduction bands; electron scattering
OSTI Identifier:
1408443
Alternate Identifier(s):
OSTI ID: 1366565