The activation of p-type doping due to nitrogen incorporation in ZnS layers deposited by MOCVD over both n(+)- and p-GaAs substrates is investigated by Raman spectroscopy. The study is realized on the substrate side by taking advantage of the high-sensitivity of the substrate-related LO phonon-plasmon (LO-P) lineshape to the carrier density in narrow gap materials. The aim in view is to give evidence for large hole transfer from the layer to the near-interfacial substrate in case of even moderate p-type doping of ZnS. The Raman response from the space charge region of the substrate remains unchanged when ZnS is deposited by using precursor diethyl-Zn (DEZn). On the contrary deep changes are observed when precursor dimethyl-Zn (DMZn) is used. These are directly related to a high doping efficiency of nitrogen in the layer. It appears indeed that the interfacial hole transfer from the DMZn-based p-ZnS layers to the n(+)- and p-substrates generate LO-P modes, respectively inside and outside the optical phonon band. These contrasted behaviors are qualitatively discussed on the basis of the dispersive and phenomenological damping approaches.