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Phonon-Suppressed Auger Scattering of Charge Carriers in Defective Two-Dimensional Transition Metal Dichalcogenides
journal contribution
posted on 2019-08-23, 19:15 authored by Linqiu Li, Ming-Fu Lin, Xiang Zhang, Alexander Britz, Aravind Krishnamoorthy, Ruru Ma, Rajiv K. Kalia, Aiichiro Nakano, Priya Vashishta, Pulickel Ajayan, Matthias C. Hoffmann, David M. Fritz, Uwe Bergmann, Oleg V. PrezhdoTwo-dimensional
transition metal dichalcogenides (TMDs) draw strong
interest in materials science, with applications in optoelectronics
and many other fields. Good performance requires high carrier concentrations
and long lifetimes. However, high concentrations accelerate energy
exchange between charged particles by Auger-type processes, especially
in TMDs where many-body interactions are strong, thus facilitating
carrier trapping. We report time-resolved optical pump-THz probe measurements
of carrier lifetimes as a function of carrier density. Surprisingly,
the lifetime reduction with increased density is very weak. It decreases
only by 20% when we increase the pump fluence 100 times. This unexpected
feature of the Auger process is rationalized by our time-domain ab initio simulations. The simulations show that phonon-driven
trapping competes successfully with the Auger process. On the one
hand, trap states are relatively close to band edges, and phonons
accommodate efficiently the electronic energy during the trapping.
On the other hand, trap states localize around defects, and the overlap
of trapped and free carriers is small, decreasing carrier–carrier
interactions. At low carrier densities, phonons provide the main charge
trapping mechanism, decreasing carrier lifetimes compared to defect-free
samples. At high carrier densities, phonons suppress Auger processes
and lower the dependence of the trapping rate on carrier density.
Our results provide theoretical insights into the diverse roles played
by phonons and Auger processes in TMDs and generate guidelines for
defect engineering to improve device performance at high carrier densities.
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Keywords
fluence 100 timescarrier lifetimescarrier densitytime-domain ab initio simulationsPhonon-Suppressed Auger ScatteringAuger processestrap statesTMDcarrier densitiesDefective Two-Dimensional Transition Metal Dichalcogenides Two-dimensional transition metal dichalcogenidesAuger processpump-THz probe measurementsphonon
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