Conductance Measurements on Pb Centres at the (111) Si:SiO2 Interface

The electrical properties of the Pb centre have been measured using the conductance technique over the temperature range 130K to 290K. A high concentration of Pb centres were created by vacuum annealing of 28nm thick thermal oxides on (111) silicon surfaces. Fitting the conductance peak allowed 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 show a capture cross-section which fell towards the band edges and which could be fitted by assuming an activated cross-section with an activation energy which increased towards the band edges. By contrast, the background states showed a cross-section which was temperature and band bending independent.