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, w...
Main Authors: | , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
AIP Publishing LLC and ACA
2017-07-01
|
Series: | Structural Dynamics |
Online Access: | http://dx.doi.org/10.1063/1.4985056 |
Summary: | 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
(
Δ
E
gap
,
Ge
,
direct
=
0.8
eV
)
and Si0.25Ge0.75
indirect gaps (
Δ
E
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 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. |
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ISSN: | 2329-7778 |