First-principle investigation of barrier height fluctuations in metal/oxide heterojunctions in relation with large tunnel current fluctuations

The ab initio electronic structure of metal/oxide heterojunctions is investigated for various interfaces simulating interface quality fluctuations. The effective barrier height for tunnel transport, taken from the relative position of the Fermi level to the bottom of the valence band, is determined in $\rm Co/Al_2O_3$ multilayers for several metal/oxide interfaces. This study introduces another origin for tunneling current fluctuations due to barrier height fluctuations related directly to the quality of the interfaces through their electronic structure. The large tunnel current dispersion resulting from small fluctuations of the interfacial oxidation level is discussed