  Purcell-enhanced quantum dot single-photon emission in the telecom C-band
from InAs quantum dots inside circular Bragg grating cavities is shown. The
InAs quantum dots are grown by means of molecular beam epitaxy on an InP
substrate and are embedded into a quaternary
$\mathrm{In}_{0.53}\mathrm{Al}_{0.23}\mathrm{Ga}_{0.24}\mathrm{As}$ membrane
structure. In a post-growth flip-chip process with subsequent substrate removal
and electron beam-lithography, circular Bragg grating ("bullseye") resonators
are defined. Micro-photoluminescence studies of the devices at cryogenic
temperatures of T = 5 K reveal individual quantum dot emission lines into a
pronounced cavity mode. Time-correlated single-photon counting measurements
under above-band gap excitation yield Purcell-enhanced excitonic decay times of
$\tau = (180 \pm 3)$ ps corresponding to a Purcell factor of $F_P = (6.7 \pm
0.6)$. Pronounced photon antibunching with a background limited $g^{(2)}(0) =
(0.057 \pm 0.004)$ is observed, which demonstrates that the light originated
mostly from one single quantum dot.
