Zirconium oxide surface passivation of crystalline silicon

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited zirconium oxide (ZrO_x). The optimum layer thickness and activation annealing conditions are determined to be 20 nm and 300 °C for 20 min. Cross-sectional transmission electron microscopy imaging shows an approximately 1.6 nm thick SiO_x interfacial layer underneath an 18 nm ZrO_x layer, consistent with ellipsometry measurements (∼20 nm). Capacitance-voltage measurements show that the annealed ZrO_x film features a low interface defect density of 1.0 × 10¹¹ cm^-2eV^-1 and a low negative film charge density of -6 × 10¹⁰ cm^-2. Effective lifetimes of 673 μs and 1.1 ms are achieved on p-type and n-type 1 Ω cm undiffused c-Si wafers, respectively, corresponding to an implied open circuit voltage above 720 mV in both cases. The results demonstrate that surface passivation quality provided by ALD ZrO_x is consistent with the requirements of high efficiency silicon solar cells.