Silicon passivation and tunneling contact formation by atomic layer deposited Al₂O₃/ZnO stacks

The passivation of Si by Al2O3/ZnO stacks, which can serve as passivated tunneling contacts or heterojunctions in silicon photovoltaics, was investigated. It was demonstrated that stacks with Al2O3 thicknesses >3 nm lead to lower surface recombination velocities (Seff,max <4 cm s-1) on n- and p-type Si than single-layer Al2O3 films for a wide range of ZnO thicknesses and irrespective of Al-doping of the ZnO. Stacks with an Al2O3 thickness of 1–2 nm were found to combine reasonable surface passivation (Seff,max = 100–700 cm s-1) with sufficiently high tunneling current densities (10–300 mA cm-2 at 700 mV).