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

Phillip Hamer,Alison Wenham,Ruy S Bonilla,Gabrielle Bourret‐Sicotte,George Martins,Peter Wilshaw

doi:10.1002/pssr.201600448

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.

Highlights

It is well established that hydrogen can be used to passivate surface and bulk defects in crystalline silicon
The reduced majority carrier concentration observed near the surface of samples treated in the plasma chamber demonstrated that significant deactivation of boron acceptors has taken place, presumably via atomic hydrogen de-activation
The most plausible explanations are that this difference is due to either etching of the silicon or the creation of signicant quantities of defects near the silicon surface through the plasma exposure [14, 15]

Summary

Introduction

It is well established that hydrogen can be used to passivate surface and bulk defects in crystalline silicon. For traditional screen-printed solar cells, hydrogen has been incorporated into dielectrics such as SiNx or AlOx that are deposited on the surface and released through high temperature firing steps [1,2,3]. There are a number of solar cell architectures, including those based on passivated contacts or traditional heterojunctions [4,5,6,7], which seek to introduce hydrogen while avoiding further high temperature processing. Hydrogen passivation can still be a critical process for these architectures and has typically been introduced either via an anneal in an environment containing molecular hydrogen, such as forming gas, or by exposure to an atomic hydrogen source, such as a remote plasma. A novel source of atomic hydrogen is demonstrated which may be valuable for these devices

Methods

Results

Discussion

Conclusion