Effective passivation of crystalline silicon surfaces by ultrathin atomic-layer-deposited TiOx layers

Abstract We characterize the surface passivation properties of ultrathin titanium oxide (TiO x ) films deposited by atomic layer deposition (ALD) on crystalline silicon by means of carrier lifetime measurements. We compare different silicon surface treatments prior to TiO x deposition, such as native silicon oxide (SiO y ), chemically grown SiO y and thermally grown SiO y . The best passivation quality is achieved with a native SiO y grown over 4 months and a TiO x layer thickness of 5 nm, resulting in an effective lifetime of 1.2 ms on 1.3 Ωcm p-type float-zone silicon. The measured maximum lifetime corresponds to an implied open-circuit voltage ( iV oc ) of 710 mV. For thinner TiO x layers the passivation quality is reduced, however, samples passivated with only 2 nm of TiO x still show a lifetime of 612 μs and an iV oc of 694 mV. The contact resistivity of the TiO x including the SiO y interlayer between the silicon wafer and the TiO x is below 0.8 Ωcm 2 . The combination of excellent surface passivation and low contact resistivity has the potential for silicon solar cells with efficiencies exceeding 26%.