Effective surface passivation of crystalline silicon using ultrathin Al₂O₃ films and Al₂O₃/SiN<i>_x</i> stacks

Abstract

Abstract We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al 2 O 3 ) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al 2 O 3 thickness. For ultrathin Al 2 O 3 layers of 3.6 nm we still attain a SRV &lt; 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al 2 O 3 films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN x ). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al 2 O 3 and SiN x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al 2 O 3 /SiN x stacks compared to the single‐layer Al 2 O 3 passivation. Al 2 O 3 /SiN x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)