Ultrafast carrier dynamics in vanadium-doped MoS alloys.

Substitutional doping is a most promising approach to manipulate the electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs). In addition to inducing magnetism, vanadium (V) doping can lead to semiconductor-metal transition in TMDCs. However, the dynamics of charge carriers that governs the optoelectronic properties of doped TMDCs has been rarely revealed. In this work, we have investigated the dynamics of photocarriers in pristine and V-doped monolayer (ML) MoS. Comparison of the transient absorption (TA) spectra of ML MoS with lightly (≤1%) and heavily (3.62%) V-doped MoS infers the induction of additional energy states in the doped materials giving rise to new low energy bleach features in the TA spectra. The quasiparticle band structure of MoS is found to disappear at sufficiently high V doping due to the presence of impurity bands. An attempt has also been made to study the manipulation of the carrier lifetime with V doping in MoS. Our TA kinetic measurements suggest that the decay kinetics of the carriers becomes slower with increasing doping percentage and at a higher doping level the carriers survive for a much longer time compared to pristine MoS. Furthermore, we have identified a new electronic transition (NET) in heavily V-doped MoS at high pump fluences.