Study of thin anodic SiO2 layers on degenerate silicon by inelastic electron tunnelling spectroscopy

Tunnelling phenomena were studied in two kinds of specimens: samples A, essentially metal—silicon junctions, featured a thin silicon oxide transition layer; samples B were prepared by the anodization of silicon in pure water. I, dI/dV and d2I/dV2vs. V curves were obtained at liquid helium temperature. For both specimens, the general shapes of the curves were in agreement with the theoretical prediction. Phonon fine structure was obtained. Moreover, for samples A, a zero-bias anomaly phenomenon, indicating the presence of metal particles in the oxide, as well as other structures, due to traps, were observed. The absence of such structures and of a zero-bias anomaly for samples B and the appearance of phonon structures, in spite of the considerably smaller amount of doping, are indications of a good quality oxide. This was in accordance with capacitance measurements made on thicker oxide obtained by the same process. These experiments show that inelastic electron tunnelling spectroscopy can be used as a valuable tool for the study of very thin silicon oxide layers in electron devices.