  Semiconductor microcavities are often influenced by structural imperfections,
which can disturb the flow and dynamics of exciton-polariton condensates.
Additionally, in exciton-polariton condensates there is a variety of dynamical
scenarios and instabilities, owing to the properties of the incoherent
excitonic reservoir. We investigate the dynamics of an exciton-polariton
condensate which emerges in semiconductor microcavity subject to disorder,
which determines its spatial and temporal behaviour. Our experimental data
revealed complex burst-like time evolution under non-resonant optical pulsed
excitation. The temporal patterns of the condensate emission result from the
intrinsic disorder and are driven by properties of the excitonic reservoir,
which decay in time much slower with respect to the polariton condensate
lifetime. This feature entails a relaxation oscillation in polariton condensate
formation, resulting in ultrafast emission pulses of coherent polariton field.
The experimental data can be well reproduced by numerical simulations, where
the condensate is coupled to the excitonic reservoir described by a set of rate
equations. Theory suggests the existence of slow reservoir temporarily emptied
by stimulated scattering to the condensate, generating ultrashort pulses of the
condensate emission.
