PO_x/Al₂O₃ stacks: Highly effective surface passivation of crystalline silicon with a large positive fixed charge

Thin-film stacks of phosphorus oxide (PO_x) and aluminium oxide (Al₂O₃) are shown to provide highly effective passivation of crystalline silicon (c-Si) surfaces. Surface recombination velocities as low as 1.7 cm s^-1 and saturation current densities J_0s as low as 3.3 fA cm^-2 are obtained on n-type (100) c-Si surfaces passivated by 6 nm/14 nm thick PO_x/Al₂O₃ stacks deposited in an atomic layer deposition system and annealed at 450 °C. This excellent passivation can be attributed in part to an unusually large positive fixed charge density of up to 4.7 × 10¹² cm^-2, which makes such stacks especially suitable for passivation of n-type Si surfaces.