Ageing of metal/ultra-thin oxide/semiconductor structures under Fowler–Nordheimcurrent injection

Abstract

In this paper, results of the ageing of metal/ultra-thin oxide/semiconductor structures underFowler–Nordheim constant current injections are presented. The oxide (silicon dioxide,SiO2) thickness layer of these structures varies from 3 to 12.5 nm for a p-type semiconductor. Itis shown that ageing induces trapped charges in the oxide layer (positive and negativenear the cathode and positive near the anode) and new interface states at theoxide/semiconductor interface.The positive charge created near the oxide/semiconductor interface,during current injection from the metal (accumulation regime,Vg<0), cannot be observed on current–voltage(I(Vg)) characteristics inthe inversion regime (Vg>0). It is shown that these charges can trap electrons injected from the semiconductor during acquisition of theI(Vg) characteristics(Vg>0). This inducesa shift in the I(Vg) characteristics as opposed to that what is obtained from capacity–voltage(C(Vg)) characteristics. So, the characteristics (density and centroid) of chargestrapped in the oxide layer cannot be obtained, as in the case of thicklayers (thickness greater than 20 nm), from the shift obtained from theI(Vg) characteristics in accumulation and inversion regimes. Also, it has been shown that thecapture of electrons by the positive charge at the oxide/semiconductor interface promotesthe creation of interface states.