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

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.