High-Quality Silicon Surface Passivation by Thermal-ALD Deposited Hafnium Oxide Films

Excellent silicon surface passivation is achieved by atomic layer deposition (ALD) grown hafnium oxide (HfOx) films on silicon surfaces (both n-type and p-type). It is inferred from the study that the silicon surface passivation by HfOx thin films is a film-thickness-dependent quality and a minimum film thickness of similar to 2 nm is essential to passivate the silicon surface. A good level of surface passivation (surface recombination velocity, SRV < 20 cm/s) can be achieved for film thickness, d >5 nm. However, the best results are obtained for hydrogen-annealed, similar to 8.5-nm-thin HfOx films. SRV as low as 3.5 cm/s (effective minority carrier lifetime, tau(eff) similar to 5 ms) and 4.4 cm/s (tau(eff) similar to 4 ms) are realized on p-type and n-type silicon surfaces, respectively. The injection level dependence of tau(eff) reveals that HfOx films provide better passivation for n-type silicon compared to p-type silicon at low injection levels. Hydrogen present in the annealing ambient first saturates the dangling bonds at the film/silicon interface and then affects the oxide charge density. Effective oxide charge density is positive in HfOx/n-Si samples and negative in HfOx/p-Si samples. This creates an accumulation condition near the silicon surface for both substrate-type situations and is responsible for effective passivation in both types of substrates. Thus, our study demonstrates that ALD-grown HfOx films offer excellent passivation for silicon surfaces.

Automated summary

Excellent silicon surface passivation is achieved by atomic layer deposition (ALD) grown hafnium oxide (HfOx) films on silicon surfaces (both n-type and p-type). The study suggests that the film thickness of the HfOx thin films plays a crucial role in the silicon surface passivation, with a minimum thickness of approximately 2 nm required for effective passivation. The best results are obtained for hydrogen-annealed, similar to 8.5-nm-thin HfOx films, which achieve a low surface recombination velocity (SRV) and high effective minority carrier lifetime (tau(eff)).