Effects of ²⁹Si and ¹H on the near-zero field magnetoresistance response of Si/SiO₂interface states: Implications for oxide tunneling currents

We report on a study that offers fundamental physical insight into an important phenomenon in solid state device physics, tunneling in Si/SiO2. We observe near-zero field magnetoresistance via spin-dependent trap-assisted-tunneling in both unpassivated and passivated Si/SiO2 and 28Si/28SiO2 metal-insulator-semiconductor (MIS) capacitors. A previous report, which utilized electrically detected magnetic resonance and NZFMR on these devices, indicates a surprising conclusion: the observed trap-assisted tunneling spectra are dominated by silicon dangling bonds back bonded to silicon at the Si/SiO2 interface, Pb0 and Pb1 centers. In this study, the four sets of samples are virtually identical, apart from the presence or absence of either 1H and 29Si. We observed a substantial narrowing of the NZFMR response with the removal of 29Si nuclei and a substantial broadening with the addition of 1H. Since superhyperfine interactions between 29Si nuclei Pb at the Si/SiO2 interface are a full order of magnitude stronger than such interactions involving silicon dangling bonds defects (E′ centers) within the oxide, the NZFMR results strongly suggest a response dominated by Si/SiO2 interface trap defects. With the introduction of 1H magnetic nuclei to the interface after a forming gas anneal, linewidths and lines shapes of Si/SiO2 and 28Si/28SiO2 MIS capacitors were nearly identical. However, the amplitude of the NZFMR response is greatly reduced by the introduction of hydrogen by a fraction about equal to the reduction in the interface trap density. Our results further indicate that the rate limiting step in trap-assisted tunneling is the interface to oxide trapping event.