Electronic Passivation of Crystalline Silicon Surfaces Using Spatial‐Atomic‐Layer‐Deposited HfO2 Films and HfO2/SiNx Stacks

Spatial Atomic Layer Deposition (SALD) is applied to the electronic passivation of moderately doped (~10^16 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 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 is attained. Reducing the HfO2 thickness to 1 nm, the passivation virtually vanishes after firing (i.e., Seff > 1000 cm/s). 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 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.