A novel source of atomic hydrogen for passivation of defects in silicon

Abstract

Palladium membranes have been used for decades for the separation of hydrogen from other gasses. In this letter the use of thin palladium leaves to act as sources of atomic hydrogen for silicon samples is explored. It has been assumed in the past that although hydrogen diffuses through palladium in atomic form, the atoms recombine to form molecular hydrogen at the surface. In this letter it is shown that hydrogen supplied to one surface of a palladium leaf can result in atomic hydrogen being released from the opposite surface at low pressure. This is demonstrated through the use of a palladium leaf in a direct plasma system which allows for atomic hydrogen to be supplied to a sample while avoiding exposure to UV radiation from the plasma and high energy charged particles. This method is shown to provide significant atomic hydrogen to silicon samples and improve passivation of silicon surfaces. Method of Shielded Hydrogen Passivation: Schematic of direct plasma chamber with a shield inserted between the plasma and the silicon sample.

Dielectric surface passivation for silicon solar cells: A review

“…They observed 2–12 times higher SRV and attributed it to the increased surface area, dangling bonds and stress‐induced defects . Most recently, Hamer et al and Bourret‐Sicotte et al reported a new methodology to extrinsically introduce H species into a SiO 2 film using a shielded ammonia plasma. By combining extrinsic chemical and FEP of SiO 2 they successfully achieved τ eff = 6.4 ms, S eff = 0.17 cm s −1 , in n‐type Si 1 Ωcm.…”

Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

“…With the development of high-quality room temperature passivation schemes such as SA-treated silicon, low-temperature gettering and hydrogenation techniques can be developed [18]- [21], which otherwise would be difficult to measure, if, for example, these methods relied on SiN x and Al 2 O 3 passivation, which in themselves can introduce hydrogen or change bulk properties through annealing procedures to activate the surface passivation (i.e., 400°C) [44]- [46]. In this regard, the SA treatment can provide valuable information regarding passivation quality of dielectric films and their impact on the bulk material.…”

“…By this procedure, an upper limit S of 3 and 13 cm/s on n-and p-type silicon are achieved, respectively [17]. From all these recent studies, it is evident that organic films can provide exceptional silicon surface passivation at very low temperatures (< 200°C), which could open up other opportunities for new and innovative low-temperature gettering and hydrogenation techniques to improve low-quality silicon for their inclusion as the base material in highly efficient solar cells [18]- [21]. However, the level of surface passivation demonstrated until now (>1 cm/s) is not good enough to compete with state-of-the-art dielectric films.…”

Shielded hydrogen passivation − A potential in‐line passivation process

“…In a recent letter, Shielded Hydrogen Passivation (SHP) was introduced as an alternative method for introducing significant amounts of atomic hydrogen at low temperatures . The approach uses plasma, in this case produced within a PECVD machine, to generate atomic hydrogen with a metal shield placed between the sample and the plasma.…”

“…In light of these studies and theoretical modelling, it has been assumed that there is a high energy barrier for the release of atomic hydrogen such that it may only occur in the presence of an additional stimulus. However, previous SHP work using Pd leaf has clearly demonstrated that a significant quantity of atomic hydrogen is released from the surface of the leaf opposite the plasma, after which it is detected by diffusion into adjacent Si material. Similar results are presented in this work.…”