Enhancing electronic materials by chemical treatments and nanoscale dielectrics

Author

Sophie Laura Pain

Year

2023

Abstract & Cover

This thesis presents a series of experiments into improved surface passivation of monocrystalline silicon, with a focus on chemical treatments and thin-film growth. A series of studies have been designed and performed for both passivation approaches.

Superacid chemical treatments offer excellent passivation of silicon (and of other electronic materials such as transition metal dichalcogenides - TMDCs), and the factors contributing to this are explored herein. A multi-material study is conducted into the behaviour of the superacid bis(trifluoromethanesulfonyl)imide (TFSA), using species with key chemical substitutions to assess the impact of functionality on passivation. The best silicon passivation is achieved by chemical treatments which introduce charge to the surface and those chemicals with CF₃SO₂ functionality, although an alternative mechanism for TMDCs must apply, as the trends observed with silicon are not consistent with those observed for TMDCs.

Superacid treatments can also be used to identify and diagnose degradation in silicon through re-passivation. The optimisation of sample processing for re-passivation is discussed, and subsequently three examples of re-passivation studies are presented. A particular focus is paid to temperature-induced degradation of Si/HfO₂ and Si/Al₂O₃, along an example of muon-induced degradation.

The latter half of this thesis focuses on silicon passivation via thin films. Ultra-thin SiO₂, Al₂O₃ and HfO₂ films are developed, with HfO₂ appearing a particularly promising ultra-thin passivation layer due to its passivation quality and negative fixed charge. Importantly, at nanoscale thicknesses, HfO₂ outperforms Al₂O₃, suggesting it is a promising alternative material for passivating interlayers of the kind which are needed for carrier selective contacts for solar cells.

Subsequently, two means to improve the passivation quality of ultra-thin HfO₂ are identified, namely the use of capping layers and chemical treatments to form chemically-enhanced passivating stacks. The improved passivation is found to be temporally stable, and resistant to further solution and thermal processing.

Source of Information

http://webcat.warwick.ac.uk/record=b3957317

University

University of Warwick

(Coventry, United Kingdom)

External Link