The role of the SiO2 interface for Al2O3 passivation layers on p-type Silicon is investigated. Thin (0.6-6.0 nm) SiO2 layers were prepared by means of HF etch and thermal oxidation on c-Si wafers prior to the Atomic Layer Deposition (ALD) of Al2O3. Subsequently, the Al2O3 layer was deposited and annealed and the films were characterized using Microwave Detected Photoconductivity (MDP), Fourier Transform InfraRed (FTIR) and Capacitance-Voltage (C(V)) measurements. The best passivation effect was found for a 2.0 nm SiO2 interface. Thicker interfaces reduce the effective minority carrier lifetime due to the formation of positive charges in the dielectric. C(V) hysteresis curves show that the charge density in Al2O3 is not stable but a function of the applied bias voltage and thickness of the SiO2 interface. The change in charge density could be described by trapping of electrons from Si into Al2O3 with SiO2 acting as a tunnel barrier. Since trapped electrons are part of the negative charges in Al2O3, a thin SiO2 interface is required to realize the high field effect passivation of Al2O3.

27th European Photovoltaic Solar Energy Conference and Exhibition; 1793-1796