Ultrafast Electron and Hole Relaxation Pathways in Few-Layer MoS<sub>2</sub>
Zhaogang Nie
Run Long
Jefri S. Teguh
Chung-Che Huang
Daniel W. Hewak
Edwin K. L. Yeow
Zexiang Shen
Oleg V. Prezhdo
Zhi-Heng Loh
10.1021/acs.jpcc.5b05048.s001
https://acs.figshare.com/articles/journal_contribution/Ultrafast_Electron_and_Hole_Relaxation_Pathways_in_Few_Layer_MoS_sub_2_sub_/2135461
Femtosecond optical pump–probe
spectroscopy is employed to elucidate the band-selective ultrafast
carrier dynamics of few-layer MoS<sub>2</sub>. Following narrowband
resonant photoexcitation of the exciton A transition, the subpicosecond
to picosecond relaxation dynamics of the electron and the hole at
the K valley are separately interrogated by a broadband probe pulse.
The temporal evolution of the spectral first moment reveals nonexponential
intravalley relaxation dynamics in the conduction band. Fluence dependence
measurements suggest that this relaxation process is predominantly
mediated by acoustic phonon emission. Intervalley scattering of carriers
from the K valley to the extrema of the conduction and valence bands
is also observed via the decay of the spectral zeroth moment. In addition,
second-order Raman scattering leads to the emergence of sidebands
in the normalized differential transmission spectra. The observed
two-phonon energies and the fluence-dependent time constants suggest
that the E<sub>1g</sub> longitudinal optical (LO) phonon and the LA
phonon participate in intervalley scattering in the conduction and
valence bands, respectively. <i>Ab initio</i> nonadiabatic
molecular dynamics simulations yield time constants of 0.80 and 0.72
ps for intra- and intervalley electronic relaxation, respectively;
the latter agrees well with experiment. Finally, the normalized differential
transmission spectra reveal a two-electron shake-up satellite that
originates from band-edge radiative recombination and the simultaneous
excitation of a hole from K<sub>v1</sub> to K<sub>v2</sub>. From its
spectral position, a K<sub>v1</sub>–K<sub>v2</sub> spin–orbit
splitting of 1166 ± 1 cm<sup>–1</sup> is deduced. The
observation of the two-electron transition points to the existence
of strong electron correlation in photoexcited few-layer MoS<sub>2</sub>.
2015-09-03 00:00:00
Ab initio nonadiabatic
MoS
conduction
2.
Fluence dependence measurements
nonexponential intravalley relaxation dynamics
broadband probe pulse
K valley
valence bands
transition
carrier
transmission spectra
Kv
picosecond relaxation dynamics
constant
intervalley
Hole Relaxation Pathways
LA
moment
electron
phonon
LO