It is shown by contactless transient photoconductivity measurements in the microwave frequency range that Si3N4 films are an outstanding passivation of the n-type c-Si surface. Si3N4 on n-type Si forms an accumulation layer, which acts as an ideally reflecting potential barrier for minority carriers (holes). Due to the small space charge layer capacitance, minority carrier storage at this interface is very limited. In contrast to the latter measurements on p-type Si wafers covered with Si3N4 are characterized by storage of excess charge carriers in the surface depletion layer. The stored charge carriers decay slowly. The minority carriers (electrons) collected at the surface show a reduced mobility. (C) 2002 Elsevier Science B.V. All rights reserved.