  Using integrated superconducting single photon detectors we probe ultra-slow
exciton capture and relaxation dynamics in single self-assembled InGaAs quantum
dots embedded in a GaAs ridge waveguide. Time-resolved luminescence
measurements performed with on- and off-chip detection reveal a continuous
decrease in the carrier relaxation time from 1.22 $\pm$ 0.07 ns to 0.10 $\pm$
0.07 ns upon increasing the number of non-resonantly injected carriers. By
comparing off-chip time-resolved spectroscopy with spectrally integrated
on-chip measurements we identify the observed dynamics in the rise time
($\tau_r$) as arising from a relaxation bottleneck at low excitation levels.
From the comparison with the temporal dynamics of the single exciton transition
with the on-chip emission signal, we conclude that the relaxation bottleneck is
circumvented by the presence of charge carriers occupying states in the bulk
material and the two-dimensional wetting layer continuum. A characteristic -2/3
power law dependence of the rise time is observed suggesting Auger-type
scattering between carriers trapped in the quantum dot and the two-dimensional
wetting layer continuum which circumvents the phonon relaxation bottleneck.
