The electrical properties of the Pb center were measured by using conductance techniques at temperatures ranging from 130 to 290K. It was found that a high concentration of Pb centers was created by the vacuum annealing of 28nm-thick thermal oxides on (111) Si surfaces. Analysis of the conductance data permitted the contribution of the (0/-) Pb level to be separated from the U-shaped background states. The (0/-) peak in the density of states was found to be asymmetrical, with a broad shoulder on the conduction-band side. The Pb levels were found to have a capture cross-section which decreased towards the band edges. It could be fitted by assuming an activated cross-section with an activation energy that increased towards the band edges. On the other hand, the background states had cross-sections which were independent of temperature and band-bending.

M.J.Uren, J.H.Stathis, E.Cartier: Journal of Applied Physics, 1996, 80[7], 3915-22