Observation of the hot-phonon effect in monolayer MoS₂

Femtosecond transient absorption measurements have been performed to study the pump wavelength- and fluence-dependent hot carrier relaxation dynamics in monolayer MoS₂. The relaxation process of the photoinduced carriers monitored within hundreds of femtoseconds after photoexcitation is demonstrated to be achieved through the carrier-phonon scattering mechanism. It is observed that an efficient hot-phonon effect can slow down the relaxation rate by around three times with the injected carrier density changing from 1 × 10¹² to 3 × 10¹³ cm^-2. A pronounced increase in the hot carrier relaxation time with decreasing temperature is further detected, which is attributed to the decreased phonon occupancy at lower temperature.