Slow states in vacuum ultraviolet irradiated metal–oxide–silicon systems

We describe a study of the generation of slow interface states (time constants ≳40 s) by vacuum ultraviolet irradiation (Kr lamp, hν=10 eV) on metal–oxide–silicon samples with approximately 30 nm of thermally grown SiO2 and a transparent aluminum gate. The density of the centers in a given energy range was obtained from the shift of the midgap voltage over this range. A detailed energy level spectrum was determined from the stabilization times of the charging or discharging current observed after each of a series of 0.1 V steps in the bias voltage. Peaks in the energy level spectrum were observed for a position of the Fermi level at the Si–SiO2 interface near the band edges, at ≊0.25 eV above the valence-band edge and at ≊0.65 eV above the valence-band edge. The corresponding defects are identified as the oxygen vacancy, the Pb center (tentatively), and a hydrogen atom trapped at an oxygen atom in a strained Si–O–Si configuration near the Si/SiO2 interface.