abstract
Spatial atomic layer deposition (SALD) is applied to the electronic passivation of moderately doped ($\approx$1016 cm$-$3) p-type crystalline silicon surfaces by thin layers of hafnium oxide (HfO2). For 10 nm thick HfO2 layers annealed at 400 °C, an effective surface recombination velocity Seff of 4 cm s$-$1 is achieved, which is below what has been reported before on moderately doped p-type silicon. The one-sun implied open-circuit voltage amounts to iVoc = 727 mV. After firing at 700 °C peak temperature in a conveyor-belt furnace, as applied in the production of solar cells, still a good level of surface passivation with an Seff of 21 cm s$-$1 is attained. Reducing the HfO2 thickness to 1 nm, the passivation virtually vanishes after firing (i.e., Seff \textgreater 1000 cm s$-$1). However, by adding a capping layer of plasma-enhanced-chemical-vapor-deposited hydrogen-rich silicon nitride (SiNx) onto the 1 nm HfO2, a substantially improved firing stability is attained, as demonstrated by Seff values as low as 30 cm s$-$1 after firing, which is attributed to the hydrogenation of interface states. The presented study demonstrates that SALD-deposited HfO2 layers and HfO2/SiNx stacks have the potential to evolve into an attractive surface passivation scheme for future solar cells.