The development of a scalable source of non-classical light is fundamental for unlocking the potential of quantum technology. The ideal source of quantum light should simultaneously deliver single and entangled photons deterministically, with high purity, high efficiency, high indistinguishability and high degree of entanglement, and it should be compatible with current photonic integration technologies. Semiconductor quantum dots are currently emerging as near-optimal sources of indistinguishable single photons. However, their performances as sources of entangled-photon pairs are still modest in comparison to state of the art sources of entangled photon states, which are based on probabilistic parametric-down-conversion processes. In general, it is believed that semiconductor quantum dots can not generate maximally entangled photon pairs, since the solid state system underlies various decoherence effects. In this thesis we use experimental and theoretical methods to investigate a material system that has received limited attention so far: droplet etched GaAs quantum dots. By coherent population of the biexciton, which is the fundamental state for the generation of entangled photon pairs in a quantum dot, we observe a near perfect single photon purity and highly entangled - albeit non maximally entangled - photon pairs. Theoretical considerations revealed that the exciton fine structure splitting is dominating the entanglement degradation. By the use of an on-chip piezoelectric strain actuator, we are finally able to cancel the fine structure splitting and perform an examination of the residual decoherence mechanism in quantum dot entanglement. The experimental work in combination with theoretical considerations allows us to demonstrate for the fist time that quantum dots can be considered as a nearly dephasing-free source of polarization entangled photons pairs on-demand. Beside the study of entanglement properties, we also investigated the indistinguishability of the emitted photons via two-photon interference experiments, where we find high, but not perfect, values of interference visibility. Based on the data we discuss the effects limiting the indistinguishability. The results presented in this thesis are of great scientific interest for future research, making quantum dot entanglement resources usable in future quantum technologies.