Insulating and passivating plasma-enhanced atomic layer deposited aluminum oxide thin films for silicon solar cells

Highlights: • Al₂O₃ thin films with different thicknesses were deposited at various temperatures • 80 nm thick Al₂O₃ films deposited at 250 °C provide sufficient electrical insulation • Al₂O₃ thin films have low defect density and low stress even after annealing • Low leakage current density and high breakdown voltage achieved after annealing • Al₂O₃ thin films enabled very good surface passivation after anneal at 450 °C - Abstract: Plasma-enhanced atomic layer deposited (PEALD) aluminum oxide (Al₂O₃) thin film were investigated with respect to their application in silicon solar cells where not only excellent surface passivation but also excellent electrical insulation properties are required. In this study, the insulation properties of about 10 nm to almost 250 nm Al₂O₃ thin films, deposited at temperatures in the range of 100 °C to 350 °C and annealed in the range of 250 °C to 450 °C, were correlated to various thin film properties, most notably the thin film defect density, i. e. pinhole density, and the thin film stress. Al₂O₃ thin films provide sufficient electrical insulation after a post-deposition annealing step at 450 °C when deposited at 250 °C with thickness of at least 80 nm which can be attributed to a low defect density and low stress in the thin films, allowing a low leakage current density and a high breakdown voltage that was independent of the type of metals used for the electrode. Al₂O₃ thin films deposited and annealed at these temperatures enabled a very good surface passivation of silicon. These results indicate that Al₂O₃ thin films realized by PEALD are a promising candidate for silicon solar cells that rely on passivating as well as insulating thin films.