A comparative study of ultrafast carrier dynamics near A, B, and C-excitons in a monolayer MoS2 at high excitation densities

Abstract

With the growing demand for monolayer MoS2 in diverse optoelectronic applications, it is more important than ever to understand carrier behavior under varied excitation conditions and at different excitonic levels. In this article, we show that band structure, excitation wavelength, and excitation density all have a significant impact on the carrier dynamics in a monolayer MoS2. At the A and B excitation levels, an initial bandgap renormalization is detected, while band bleaching is found to play a stronger role at the C-excitonic state. The exciton dissociation at the band edge near A and B-exciton causes the bandgap renormalization. On the other hand, band bleaching, which occurs at the C-exciton, is caused by the exciton formation due to the high availability of states. At this excitation energy, carrier relaxation and thermalization occur through lattice interaction by releasing a high number of hot phonons, which creates a bottleneck effect. Due to the hot phonon bottlenecking effect, carrier relaxation time is prolonged.