Tunneling spectroscopy studies of treated aluminum oxide tunnel barrier layers

We report scanning tunneling microscopy and ballistic electron emission microscopy studies of the electronic states of the uncovered and chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states change when chemisorbed oxygen ions are moved into the oxide by either flood gun electron bombardment or by thermal annealing. While untreated samples exhibit band tails extending to zero bias, the former, if sufficiently energetic, results in locally well defined conduction band onsets at ∼1V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 °C thermal anneals.