  We demonstrate experimental results based on time-resolved photoluminescence
spectroscopy to determine the oscillator strength (OS) and the internal quantum
efficiency (IQE) of InGaAs quantum dots (QDs). Using a strain-reducing layer
(SRL) these QDs can be employed for the manufacturing of single-photon sources
(SPS) emitting in the telecom O-Band. The OS and IQE are evaluated by
determining the radiative and non-radiative decay rate under variation of the
optical density of states at the position of the QD as proposed and applied in
J. Johansen et al. Phys. Rev. B 77, 073303 (2008) for InGaAs QDs emitting at
wavelengths below 1 $\mu$m. For this purpose, we perform measurements on a QD
sample for different thicknesses of the capping layer realized by a controlled
wet-chemical etching process. From numeric modelling the radiative and
nonradiative decay rates dependence on the capping layer thickness, we
determine an OS of 24.6 $\pm$ 3.2 and a high IQE of about (85 $\pm$ 10)% for
the long-wavelength InGaAs QDs.
