Using Atom-Probe Tomography to Understand ZnO:Al/Si O2/Si Schottky Diodes

We use electronic transport and atom-probe tomography to study ZnO:Al/SiO2/Si Schottky diodes on lightly doped n- and p-type Si. We vary the carrier concentration in the ZnO:Al films by 2 orders of magnitude, but the Schottky barrier height remains nearly constant. Atom-probe tomography shows that Al segregates to the interface, so that the ZnO:Al at the junction is likely to be metallic even when the bulk of the ZnO:Al film is semiconducting. We hypothesize that the observed Fermi-level pinning is connected to the insulator-metal transition in doped ZnO. This implies that tuning the band alignment at oxide/Si interfaces may be achieved by controlling the transition between localized and extended states in the oxide, thereby changing the orbital hybridization across the interface.