Search

The alneal is one of the most effective methods of electrically passivating a silicon surface, and has been used by numerous research groups since the 1980s. In this work, we present an enhanced alneal process that substantially improves its effectiveness. Previously, the success afforded by the standard alneal has been attributed to the chemical passivation provided by hydrogenation of the Si-SiO 2 interface. However, the work presented here shows that it is possible to enhance the surface passivation by simultaneously introducing a component of Field Effect Passivation (FEP). Where the standard alneal is seen to provide lifetimes of ~2.1 ms, equivalent to a surface recombination velocity (SRV) of 3.3 cm/s, the enhanced alneal can provide a lifetime of 5.6 ms on 1 Ω cm, n-type Si, equivalent to a SRV 0.4 cm/s. The charge required for this enhanced passivation can be introduced in the order of minutes and has the potential to be introduced at the same time as the aluminium is deposited, thus, resulting in no extra processing time. Secondary ion mass spectroscopy showed that the nature of the charge is likely to be K and Na cations residing at the Si-SiO 2 interface. The possibility of increasing the surface passivation beyond that of the standard alneal points to the importance of both chemical and field effect components of passivation, and is therefore of significant interest to high efficiency silicon solar cell research. [ABSTRACT FROM AUTHOR]

This paper reports a new approach for exposing materials, including solar cell structures, to atomic hydrogen. This method is dubbed Shielded Hydrogen Passivation (SHP) and has a number of unique features offering high levels of atomic hydrogen at low temperature whilst inducing no damage. SHP uses a thin metallic layer, in this work palladium, between a hydrogen generating plasma and the sample, which shields the silicon sample from damaging UV and energetic ions while releasing low energy, neutral, atomic hydrogen onto the sample. In this paper, the importance of the preparation of the metallic shield, either to remove a native oxide or to contaminate intentionally the surface, are shown to be potential methods for increasing the amount of atomic hydrogen released. Excellent, damage free, surface passivation of thin oxides is observed by combining SHP and corona discharge, obtaining minority carrier lifetimes of 2.2 ms and J 0 values below 5.47 fA/cm 2 . This opens up a number of exciting opportunities for the passivation of advanced cell architectures such as passivated contacts and heterojunctions. [ABSTRACT FROM AUTHOR]

Shielded hydrogen passivation (SHP) is a recently developed technique for introducing atomic hydrogen into materials and it offers significant advantages over the other hydrogenation techniques. Hydrogen de-activation of boron followed by electrochemical CV profiling was used to demonstrate that substantial quantities of atomic hydrogen can permeate though palladium/silver alloy foils which are 10 µm thick. It is thought that such thickness will be sufficient to withstand pressures of up to 1 atmosphere allowing passivation in an in-line process. Further, it is shown that poisoning of the foil by using sulphur increases the flux of atomic hydrogen released. SHP delivers extremely good passivation of SiO2-Si interfaces, as demonstrated by using thermally oxidised 1 Ω-cm, n-type silicon where the lifetime, at 1015 cm−3 injection level, was found to increase from 12 to 1.05 ms after SHP processing. Upon application of corona charge, the lifetime further increased to 6.3 ms, equivalent to SRV ≤ 0.17 cm s−1. [ABSTRACT FROM AUTHOR]