Effect of F-inclusion in nm-thick MgO tunnel barrier

We investigated the electrical characteristics of MgO tunnel barriers while we add F during oxidation process of nm-thick Mg layer. Specifically we measured dI/dV and d2I/dV2 data of MgO tunnel barriers as we add F. When comparing the data of magnesium oxyfluoride tunnel barriers to those of aluminum oxyfluoride data, we have found that effect of F-inclusion in MgO is different from that in AlOx; F-inclusion in MgO barrier makes the barrier more symmetric while F-inclusion in AlOx barrier makes the barrier more asymmetric. However, the d2I/dV2 data of MgO did not change much even after F-inclusion, suggesting a very small amount of F-doping can make significant change in oxidation process of nm-thick Mg layer. We believe this result from the fact the oxidation process of nm-thick Mg layer is reaction-limited while the oxidation process of Al layer is diffusion-limited.