Investigation of Radiation-Induced Interface States Utilizing Gated-Bipolar and MOS Structures

The radiation dose dependence of the energy profile of the interface state density, NFS(E), has been monitored for the first time by using quasistatic MOS C-V techniques. The surprising result is that the radiation-induced increases in the interface state density are proportional to the pre-irradiation density regardless of the energy position in the band gap (away from the band edges) and in spite of the differences in the nature of the pre-and post-irradiation interface states. Both undoped and aluminum-implanted silicon dioxide films were used in the MOS devices investigated in this effort. Also, the dose dependence of the capture crosssection for carriers, ¿, has been determined for the first time by combining quasistatic MOS capacitance measurements with gate-controlled IEBO measurements. Initial cross section values were consistent with those determined by different techniques, ~6×10-16 cm2. Contrary to the results that have been reported by other workers, ¿ was found to be relatively constant with respect to changes in NFS. Consequently, the radiation-induced rise in the surface recombination velocity is interpreted as being primarily due to an increase in NFS.