ANNEALING EFFECTS AND OXIDE STRUCTURE IN ALUMINA TUNNELING BARRIERS

In this work we have studied changes in aluminium-oxide-aluminium tunnel barrier parameters that result from annealing at different temperatures with and without an applied potential difference. We identify two processes: irreversible increase in mean barrier height which takes place under all conditions and reversible changes in the internal field produced by applied bias. We explain the observations in terms of a detailed microscopic model involving excess Al3+ in the barrier region and field-induced movement of ions. The model implies that the oxide grows by the classic Cabrera-Mott mechanism with aluminium as the mobile species, and it sheds light on the nature of the oxide and of the interfacial regions in this technologically important system.