Study of Tunnel Currents of Electrons and Holes in Thermal SiO₂ with Charge Accumulation in the Dielectric^†

Accumulation of positive and negative charges in the structures metal–silicon nitride (300 nm)–tunnel thick SiO₂ sublayer (5 to 10 nm)–silicon in fields of (6 to 20) × 10⁶ V/cm is studied. A dependence of the accumulation current of electrons and holes on the reverse electric field in a dielectric is obtained on the basis of data on charge accumulation. The dependence obtained for electrons corresponds to the carrier injection from silicon according to the Fowler-Nordheim mechanism. Possible mechanisms of positive charge accumulation are discussed. The obtained anomalously high value of the exponential in the dependence of accumulation current on the reverse field equal to 7.5 × 10⁸ V/cm, and is assumed to be due to tunnel injection. For this case an estimation for the effective mass of holes in the forbidden zone of SiO² of about 2.5m_e is obtained.