Transport properties in a new type of modulation doped InP/InGaAs systems, where the n-type doping is provided by intrinsic PIn-antisite defects rather than foreign impurities, are studied by Shubnikov-de-Haas (SdH) oscillations and low-field Hall effect measurements. A close comparison of transport properties is made between these intrinsically modulation doped structures with extrinsically doped structures, with the emphasis on two of the most important physical processes i.e. doping efficiency and scattering mechanism. It is found that the efficiency of the intrinsic modulation doping is at least as high as the extrinsic modulation doping. The mobilities of the two dimensional electron gas (2DEG) derived from Hall and SdH measurements are shown to be higher in the intrinsically doped structures as compared to the extrinsically doped structures. This is attributed to a reduced scattering of the 2DEG by the remote parent dopants, due to e.g. an increased screening of the scattering potential by the excess free electrons present in the intrinsic doping region due to auto-ionization of the P_In antisite.