  The biexciton-exciton emission cascade commonly used in quantum-dot systems
to generate polarization entanglement yields photons with intrinsically limited
indistinguishability. In the present work we focus on the generation of pairs
of photons with high degrees of polarization entanglement and simultaneously
high indistinguishability. We achieve this goal by selectively reducing the
biexciton lifetime with an optical resonator. We demonstrate that a suitably
tailored circular Bragg reflector fulfills the requirements of sufficient
selective Purcell enhancement of biexciton emission paired with spectrally
broad photon extraction and two-fold degenerate optical modes. Our in-depth
theoretical study combines (i) the optimization of realistic photonic
structures solving Maxwell's equations from which model parameters are
extracted as input for (ii) microscopic simulations of quantum-dot cavity
excitation dynamics with full access to photon properties. We report
non-trivial dependencies on system parameters and use the predictive power of
our combined theoretical approach to determine the optimal range of Purcell
enhancement that maximizes indistinguishability and entanglement to near unity
values, here specifically for the telecom C-band at $1550\,\mathrm{nm}$.
