Optical properties of short-period CdSe/ZnSe fractional monolayer (ML) superlattices (SLs) with nominal thickness of CdSe layers in the range of 0.1-2 ML have been studied, focusing on vertical carrier transport along the growth axis. Specially designed structures have been grown by molecular beam epitaxy, containing either a single SL or a SL with an enlarged ZnCdSe quantum well located far away from the region where carriers are generated by photo-excitation. Extremely efficient vertical transport is observed for a CdSe layer thickness less than 0.7 ML, confirming formation of a perfect miniband of extended states. Localized electronic levels appear in the SL with CdSe layers thicker than 0.7 ML. However, at layer thicknesses up to 1-1.5 ML the extended states dominate the light-absorption process and the transport properties of the SL.