Dissertation in the field of Semiconductor Technology, Ville Vähänissi
The title of thesis is ”Boron and phosphorus diffusion gettering: Efficiency, mechanism and applicability to silicon solar cells”
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Impurities are, and have always been, an issue in silicon technology due to their detrimental effects on device performance. As it is impossible to completely prevent the presence of impurities in device processing, various defect engineering strategies are essential. The purpose of this thesis is to increase the level of understanding of different impurity gettering techniques in silicon, especially from solar cell point-of-view.
The results obtained in the thesis consist of both material parameters, such as minority carrier lifetime and bulk impurity concentration, and device parameters, such as solar cell Voc, Jsc and η. The conducted experiments determine the obtainable gettering efficiencies and help to clarify the exact mechanisms behind gettering. Special emphasis is put on analyzing the applicability of the different gettering techniques to silicon solar cells. The results clearly demonstrate the importance of careful process parameter design. The most effective gettering mechanisms are found to be case sensitive. To achieve best results, the gettering parameters used for high purity silicon should be chosen differently as for a material with high impurity content.
Many of the themes covered in the thesis, e.g. n-type silicon, oxygen precipitation and related defects, red zone removal and implantation gettering, coincide closely with the topics under current debate in the photovoltaic community.
Opponent: Professor John Murphy, University of Warwick, United Kingdom
Supervisor: Professor Hele Savin, Aalto University School of Electrical Engineering, Department of Micro- and Nanosciences
Contact information:
Ville Vähänissi
tel +358 50 4317 397
ville.vahanissi@aalto.fi