We discuss the potential applications of single photon sources based on a single quantum dot, emphasizing the crucial importance of the efficiency parameter in view of applications in the field of quantum computing and quantum communications. By inserting the single quantum dot in a pillar microcavity, an efficiency as high as 44% has been obtained by using the Purcell effect. We show that this approach is limited in practice by extrinsic cavity losses, such as those related to the scattering by the sidewalls roughness. We present novel design rules for micropillars in view of this application and show that for the well-mastered GaAs/AlAs system more than 70% of the emission can be concentrated into the collimated emission beam associated with the fundamental cavity mode. We show finally that a novel design, based on a state-of-the-art 2D photonic crystal microcavity, could permit to reach efficiencies in excess of 0.95.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.