A spin-dependent recombination study of radiation-induced P b1 centers at the (001) Si/SiO2 interface

The generation of interface defects at the Si/SiO2 boundary is an important aspect of radiation damage in MOS devices. The observations of several independent groups over the last twenty years have demonstrated that Si/SiO2 interface silicon "dangling bond" defects called P-b centers dominate the interface trap generation process. In the technologically important (001) Si/SiO2 system, two Pb variants may appear. One variant, the P-b0 center, generally dominates radiation and hot carrier damage; however, a less web studied variant, called P-b1 may play a significant secondary role. The electronic properties of the Pbl centers are quite controversial. Early work by Gerardi ct al.indicated quite strongly that the Pbl centers, like the other Pb family members, have two levels in the Si bandgap. Several recent publications by Stesmrtns and Afanas'ev argue that P-b1 centers do not have any levels in the Si bandgap. We present spin-dependent recombination (SDR) measurements which demonstrate that Pbl centers have levels around the middle of the Si bandgap. Our SDR results strongly suggest that the Pbl center electron correlation energy is significantly smaller than that of P-b0 Our results may help explain some apparently contradictory studies involving the energy distribution of radiation induced interface states. We also discuss possible relevance of these results to the precision of oxide charge measurements based on the shifts in capacitance versus voltage curves for the Fermi energy at midgap.