  Strong Coulomb interactions in two-dimensional systems, together with quantum
confinement, make many-body processes particularly effective for carrier
dynamics, which plays a crucial role in determining carrier lifetime,
photoconductivity, and emission yield of the materials. Hereby, by using
optical pump and terahertz probe spectroscopy, we have investigated the
photocarrier dynamics in the PdSe2 films with different thickness. The
experimental results reveal that the photocarrier relaxation consists of two
components: a fast component of 2.5 ps that shows the layer-thickness
independence, and a slow component has typical lifetime of 7.3 ps decreasing
with the layer thickness. Surprisingly, the relaxation times for both fast and
slow components are exhibited both pump fluence and temperature independence,
which suggests that synergistic interactions between defect trapping and Auger
effect dominate the photocarrier dynamics in PdSe2 films. A model involving
defect-assisted Auger process is proposed, which can reproduce the experimental
results well. The fitting results reveal that the layer dependent lifetime is
determined by the defect density rather than carrier occupancy rate after
photoexcitation. Our results underscore the interplay between Auger process and
defects in two-dimensional semiconductors.
