Raman Spectroscopic Study of Nb/AlO x –Al/Nb Josephson Junctions

We have studied the AlO x barrier composition of niobium (Nb) Josephson junctions with a Nb/AlO x -Al/Nb structure using Raman spectroscopy at 10 K. We have observed both Al-O and Al-OH modes of an AlO x barrier with a few nm thickness in the Raman spectra through Nb counter electrode. For a structure annealed at 300°C, the Al-O mode intensity increases and the Al-OH mode intensity decreases. This contributes to a change in the critical current of the junction after annealing.