Interface state degradation of metal/ultra-thin oxide/semiconductor structures under electron injections at high field

In this paper we analyze the interface states of metal/ultra thin oxide/semiconductor structures and their degradation under electron injection from the metal or the semiconductor, by the Fowler-Nordheim effect, at high electric field (>10 MV/cm). The metal used is chromium and the oxide layer thickness is in the range of 60 Å-130 Å. Before injection the energy distribution of the interface states in the semiconductor gap presents a peak of energy of 0.25 eV above the semiconductor valence band edge. The peak density (Nssmax) decreases with the oxide thickness. After injection the degradation of the Nssmax density depends on the oxide thickness, and increases with injected charge independently of the injected field and the polarization mode (V<0, V>0) of the structure for the high injected charge (Qinj>2.10^-1 c/cm²). The injection influence on the interface state density (Nssmid) at mid gap is not important. The Nssmid density is lower than 10¹⁰ eV^-1 cm^-2 for all the injection charges (V<0, V>0). Also, we showed that the sensitivity to the degradation by electron injection decreases with the oxide thickness. In comparing with the literature results, we deduced a lower interface state density for our structures, and a satisfactory sensitivity to the degradation to high injecting fields.