Ultrafast electron transport in layered semiconductors studied with femtosecond-laser photoemission

Femtosecond-laser photoemission was used to investigate the electron dynamics in the layered semiconductors MoSe₂ and WSe₂. Photoexcitation with 200-fs pulses of 2.03 eV light creates an electron gas with significant excess energy. Our measurements reveal a strong transient enhancement in the diffusive transport of the most energetic electrons relative to the conduction-band minimum. Additionally, we demonstrate that the surfaces of these layered chalcogenides are electronically passivated and we give an upper bound for the density of defect states within the band gap.