Si-rich silicon nitride (SiNx(:H)) films are deposited on single crystalline p-type silicon to investigate their properties as a passivation and antireflection coating for solar cells. The SiNx(:H) films were reactively sputtered from an intrinsic Si-target in an Ar/N-2/H-2 rf(13.56 MHz) magnetron plasma at substrate temperatures from 150 degrees C to 350 degrees C. The optical band gap of Si-rich SiNx(:H) becomes lower than 3 eV which was determined from spectral data of the complex refractive index. Infrared spectra show a strong Si-H band in Si-rich films. The effective surface recombination velocity (SRV) was calculated from the effective life time in SiNx(:H) covered p-Si wafers by the microwave detected photoconductivity decay (MW PCD) technique. Very low values for the effective SRV of about 60 cm/s were determined. The low values of the effective SRV are due to field-effect passivation. The field-effect passivation of the SiNx(:H)/Si contact is explained with the model of a hetero junction.