Ultrafast carrier thermalization and trapping in silicon-germanium alloy probed by extreme ultraviolet transient absorption spectroscopy
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 Si0.25Ge0.75 by extreme ultraviolet transient absorption spectroscopy. Probing the photoinduced dynamics of charge carriers at the germanium M4,5-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 (ΔEgap,Ge,direct=0.8 eV) and Si0.25Ge0.75 indirect gaps (ΔEgap,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 Si0.25Ge0.75 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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jun 06, 2017
- Source ID
- 10.1063/1.4985056
Entities
People
- Andrey Gandman
- Chaitanya D. Pemmaraju
- Christopher J. Kaplan
- Daniel Neumark
- David Prendergast
- Hung-Tzu Chang
- James S. Prell
- Lauren J. Borja
- Michael Zürch
- Myoung Hwan Oh
- Peter M. Kraus
- Scott K Cushing
- Stephen R. Leone
Organizations
- Air Force Office of Scientific Research
- Alexander von Humboldt Foundation
- Army Research Office
- Defense Advanced Research Projects Agency
- Lawrence Berkeley National Laboratory
- National Institutes of Health
- Office of Energy Efficiency and Renewable Energy
- SLAC National Accelerator Laboratory
- Swiss National Science Foundation
- United States Department of Energy
- W. M. Keck Foundation
- Yusuf Hamied Department of Chemistry