Investigation of both interface states spectrum and deep oxide states from differential isothermal transient spectroscopy

Metal/insulator/Si (MIS) structures using a high-permittivity (high-k) dielectric layer, here the perovskite compound SrTiO₃, are investigated by differential isothermal transient spectroscopy in order to study electronic states at interface and inside the oxide. The isothermal transient capacitance responses of these MIS capacitors, obtained at varying depletion bias voltages and recording times, are analysed by fast Fourier transform (FFT). Different values of the accumulation pulse duration may induce changes in the trapped charge, allowing identification of the various mechanisms for restoring thermodynamical equilibrium in the interface states. Thus, discrimination between the proper contribution of interfaces states and that of oxide deep states is evidenced. The effects of several post-annealing of the oxide layer onto the energy spectra are also described.