Relationship between passivation properties and band alignment in O3-based atomic-layer-deposited AlO_x on crystalline Si for photovoltaic applications

The passivation properties and band structures in aluminum oxide (AlO_x) deposited by ozone-based atomic layer deposition (ALD) at room temperature on p-type crystalline silicon were investigated by X-ray photoelectron spectroscopy (XPS). The effective carrier lifetime depends on the thickness of AlO_x films, since the field effects induced in the films by fixed charges depend on film thickness. The fixed charges are different by two orders of magnitude between films with thicknesses of 10 and 30 nm. At the 30-nm-thick AlO_x/Si interface, the completely accumulated band bending of the Si surface was observed. On the other hand, a thin depletion layer was formed at the 10-nm-thick AlO_x/Si interface. From the timedependent XPS measurements, a hole trap was observed toward AlO_x, in which trapping centers existed.