Rutherford backscattering and X-ray reflectivity analysis of tunnel barriers

The properties of the insulating barrier junctions are determinant to the properties of silicon-based spin transistors. They are strongly influenced by their layer thicknesses and composition. Hence, forming the barrier is a key factor in fabricating a functional device. In this work, we investigate the formation of zirconium oxide and mixed zirconium and aluminium oxide ultra-thin barriers, by deposition of 5 to 10 Å thick Zr and/or Al layers which are then oxidised in a remote Ar/O2 plasma on a previously smoothed Si wafer. We determine the thickness and composition of the layers using a combination of grazing angle Rutherford backscattering and X-ray reflectivity. We study the oxidation of the Zr and Al layers, and show that, within the sensitivity of the experiments, no diffusion between the barriers and the Si substrate occurred.