Interfacial character and electronic passivation in amorphous thin-film alumina for Si photovoltaics

The development of Si photovoltaic architectures using n-type base elements has prompted the investigation of alumina thin films as alternative passivation coatings for p-type Si to enhance photocarrier extraction and improve overall energy-conversion efficiency. The relationship between interfacial chemistry and nanostructure and electronic passivation performance was examined in amorphous alumina films, grown using a high-throughput plasma enhanced chemical vapor deposition (PECVD) method onto p-type Si wafers. The specimens were subjected to a range of post-deposition isothermal annealing treatments. Minority carrier lifetime (τ) was measured using resonance-coupled photoconductive decay (RCPCD) and was related to the evolution of interfacial roughness as well as near-interface oxygen-aluminum ratio throughout the iterative thermal treatments. An annealing time of 6 minutes at 500°C under a nitrogen atmosphere produced the greatest enhancement in both fixed space charge at the interface and carrier lifetime observed in this study, consistent with a field-based passivation response. From the correlation established between passivation performance and interfacial structure and chemistry, a mechanistic interpretation of the relationship between thermal processing, nanostructure, and passivation-related properties is offered in the context of an alumina passivation coating produced using an industrial-scale synthesis method.