Excellent Passivation of n-Type Silicon Surfaces Enabled by Pulsed-Flow Plasma-Enhanced Chemical Vapor Deposition of Phosphorus Oxide Capped by Aluminum Oxide

Phosphorus oxide (PO_x) capped by aluminum oxide (Al₂O₃), prepared by atomic layer deposition (ALD), has recently been introduced as a surface passivation scheme for planar n-type FZ silicon. In this work, a fast pulsed-flow plasma-enhanced chemical vapor deposition (PECVD) process for the PO_x layer is introduced, making it possible to increase the PO_x deposition rate significantly while maintaining the PO_x/Al₂O₃ passivation quality. An excellent surface passivation is realized on n-type planar FZ and Cz substrates (J₀ = 3.0 fA cm⁻²). Furthermore, it is demonstrated that the PO_x/Al₂O₃ stack can passivate textured surfaces and that the application of an additional PECVD SiN_x capping layer renders the stack stable to a firing treatment that is typically used in fire-through contact formation (J₀ = 12 fA cm⁻²). The excellent surface passivation is enabled by a high positive fixed charge density (Q_f ≈ 4 × 10¹² cm⁻²) and an ultralow interface defect density (D_it ≈ 5 × 10¹⁰ eV⁻¹ cm⁻²). Finally, outstanding passivation is demonstrated on textured silicon with a heavy n⁺ surface doping, as is used in solar cells, on par with alnealed SiO₂. These findings indicate that PO_x/Al₂O₃ is a highly suited passivation scheme for n-type silicon surfaces in typical industrial solar cells.