Characteristics of surface passivation of ozone- and water-based Al2O3 films grown by atomic layer deposition for silicon solar cells

Highlights: • We compared surface passivation of ozone- and water-based ALD-Al₂O₃ film. • Ozone-based ALD-Al₂O₃ film shows excellent thermal stability for passivation. • The passivation quality of O₃-based Al₂O₃ is affected by interface defect over 780 °C. • Degradation of passivation performance was different according to ALD oxidants. - Abstract: We investigated the effects of the thermal stability of atomic layer deposition (ALD) oxidants on the surface passivation of ALD-Al₂O₃ film. The results showed good passivation at temperatures not greater than 780 °C. However, we found that Al₂O₃ films with an ozone oxidant showed better surface passivation at high temperatures than the water-based samples. The Al₂O₃ films with a water oxidant yielded an additional interfacial oxide upon high-temperature annealing. In the case of the ozone-based samples, the interfacial SiO bonds that formed during deposition were more stable. This structural change degraded chemical passivation, which increased the interface-trap density to ~10¹² eV⁻¹ cm⁻². The passivation performance of ALD-Al₂O₃ films showed that at temperatures over 780 °C the passivation quality was affected more by defective passivation at the Si/SiOx interface than by a negative-fixed charge.