Oxygen stoichiometry and instability in aluminum oxide tunnel barrier layers

Abstract

We present X-ray photoelectron spectroscopy data which show that the chemisorbed oxygen previously observed to be on the surface of thin AlO x layers formed by room temperature thermal oxidation is bound by oxygen vacancies in the oxide. Increasing the electric field across the oxide, either by over-coating with a metallic electrode, or by electron bombardment, drives this surface chemisorbed oxygen into the vacancy sites. Due to the low bonding energies of these oxygen sites, subsequent oxygen exposures draw these

Atomic and electronic structure of ultra-thin Al/AlOx/Al interfaces

“…Regions of similar barriers, referred to as "hot spots", were also observed by Gloos et al [2]. An interesting study by Tan et al [4] points to a novel stabilisation in the oxidation process and an inherent instability in AlO x films. They find that two structures -one corresponding to x ≈ 1.2 and the other with x ≈ 1.0 -can be switched using an electron gun, by exposure to oxygen or by overlaying the oxide with a metal having the work-function different from Al.…”

“…Practically this means that in typically prepared disordered interfaces the local geometric and electronic structure of the "asymmetric" type will be more frequent than the one of the "symmetric type". Furthermore, due to their energetic proximity, it is not surprising that one can switch between them, as it has been indeed experimentally done by Tan et al [4] by means of electron bombardment or by overcoating with metals having different work function (Au in our case and Y, Nb, and Co by Tan et al [4]). The calculated interface energy as well as the fact that using the Au electrode in place of the Al one drives the system towards the transition A → S, represents further evidence that the experimentally observed behaviour by Tan et al corresponds to the transition between local asymmetric and symmetric structures presented in our paper.…”

Electrical stress effect on Josephson tunneling through ultrathin AlOx barrier in Nb/Al/AlOx/Nb junctions

“…contains a large amount of oxygen vacancies. [35] At the oxidation conditions used in our work, the barrier thickness is only ∼ 1 nm, i.e. just about two to three nearestneighbor distances.…”

Thermally stable pn-junctions based on a single transparent perovskite semiconductor BaSnO3

“…5,6 In manganates, the interfacial magnetic properties were unreliable in magnetic tunnel junctions, due to its oxygen instability. [7][8][9] In resistively switched NiO, the very movement of oxygen seems responsible for the switching, making the controllability difficult. 10,11 In titanates, the oxygen stoichiometry issue at the interface remains controversial to date in spite of huge on-going interest in their 2DEG-like properties.…”