Simultaneous dark-current and flat-band-voltage measurements on metal-Si3N4-Si capacitors were used to deduce Si-Si 3N4 contact-current-contact-field characteristics under positive and negative voltage bias. Whereas total-current-average-field characteristics are functions of counterelectrode material and nitride thickness, these contact-current-contact-field characteristics were dependent solely on the local properties of the Si-Si3N4 interface. Fowler-Nordheim analysis of the contact characteristics assuming 2-eV barrier heights as determined by internal photoemission indicated low effective masses of 0.05-0.13m0 for electrons and 0.005m0 for holes. Alternatively, use of an effective mass of 0.4m0 (as observed in SiO2) led to effective barrier heights of 0.8-1.2 eV for electrons and 0.44 eV for holes. Several mechanisms, including trap-assisted tunneling, are discussed which could account for different dark-current and photoemission barrier heights. In addition, simultaneous photocurrent and flat-band-voltage measurements as a function of voltage bias were performed to assist in determining the dominant photocurrent carrier type (electrons or holes) and the limiting photocurrent mechanism (contact or bulk).