Passivation Of Defects In Silicon Research Articles

Hydrogen diffusion and dissociation influenced by the laser treatments: a study in the context of silicon processing

Diffusion of hydrogen and thus passivation of defects in silicon that can facilitate the fabrication of high-efficiency solar cells using low-cost silicon material mostly rely on the thermal treatment. In this contribution, we aim to investigate the effect of diode laser-induced thermal treatment on the hydrogen diffusion as well as the passivation of crystallographic defects in silicon and eventually open-up the window to employ lasers in achieving the high effectiveness in passivation. To do so, we employed a robust numerical model, which is developed in an open-source based computational fluid dynamics (CFD) platform, to explain the coupled thermal and diffusion-reaction phenomena initiated as well as controlled by the lasers. The results reveal some interesting insights into the considerable concentrations of hydrogen and the effective passivation of defects throughout the silicon substrate that will help in achieving the desired outcome in fabricating high-efficiency solar cells. Such as, with prolonged exposure times during the laser annealing, the bulk of the silicon substrate becomes recombination-active and eventually enables the possibility of conducting defect passivation, however meanwhile, enables the dissociation of hydrogen from the defect sites. While the dissociation of hydrogen can be controlled by employing short exposure times during laser annealing, the penetration length of hydrogen inside the substrate has to be considered as short exposure times result in a passivation-active region remain confined at the surface vicinity. The findings from this study will help as a valuable resource in further optimising the operating parameters during laser-induced thermal treatment.

A novel source of atomic hydrogen for passivation of defects in silicon (Phys. Status Solidi RRL 5/2017)

A novel source of atomic hydrogen for passivation of defects in silicon (Phys. Status Solidi RRL 5/2017)

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

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.

Manipulation of Hydrogen Charge States for Passivation of P-Type Wafers in Photovoltaics

Passivation of defects in silicon solar cells using hydrogen has long been an area of significant interest to the photovoltaic community. In this paper, we explore the importance of the charge states of hydrogen for passivation of defects in p-type silicon and how these charge states might be manipulated using illumination. We show that by using illumination during hydrogenation processes at temperatures between 475 and 625 K, the lifetime of wafers containing high concentrations of hydrogen can be strongly increased. The magnitude of the increase depends on temperature, with the most significant increase occurring at 545 K with samples under illumination showing an average effective lifetime of 167 μs, while samples without illumination had an average lifetime of 67 μs. This increase in the lifetime with illumination is explained in terms of how the electron quasi-Fermi energy and, hence, the relative concentrations of the hydrogen charge states respond to illumination at these temperatures. We show a correlation between the predicted charge states of interstitial hydrogen and the effective lifetimes of the wafers.