  We present a theoretical model that allows us to describe the dynamics of
exciton polaritons in the strong-coupling regime in a monolayer WS2 based
semiconductor microcavity. Numerical simulations using Boltzmann equations give
an overall description of polariton kinetics over a temperature range of
130-230K, under nonresonant excitation. Here, only the scattering rate via
optical phonons (LO) from the upper (UP) towards lower (LP) polariton branches
is considered. According this model we show the importance of the radiative
lifetime of the polaritonic states relative to polariton relaxation rate. Our
results show as the cavity detuning changes from negative (130 K) to positive
(230 K) values, the UP branch can be tuned from a more excitonlike to a more
photonlike state at small wave vector k. We deduce that the UP states have a
faster lifetime and the polariton relaxation time into the LP energy states
becomes very efficient. Thus, the UP occupation starts to decrease, and we
observe a simultaneous increase in the occupation of the LP branch.
Furthermore, the polariton states are less occupied for small excitation pump
rate, the calculated behavior is linear. In the high pumping regime, we observe
the nonlinear behavior of cavity polaritons and occupation factors much larger
than unity are reached.
