Details

Autor(en) / Beteiligte

• Grant, Nicholas E.
• Markevich, Vladimir P.
• Mullins, Jack
• Peaker, Anthony R.
• Rougieux, Fiacre
• Macdonald, Daniel

Titel

Thermal activation and deactivation of grown-in defects limiting the lifetime of float-zone silicon

Ist Teil von

• Physica status solidi. PSS-RRL. Rapid research letters, 2016-06, Vol.10 (6), p.443-447

Ort / Verlag

Berlin: WILEY-VCH Verlag Berlin GmbH

Erscheinungsjahr

2016

Quelle

Wiley Online Library

Beschreibungen/Notizen

• By studying the minority carrier lifetime in recently manufactured commercially available n‐ and p‐type float‐zone (FZ) silicon from five leading suppliers, we observe a very large reduction in the bulk lifetime when FZ silicon is heat‐treated in the range 450–700 °C. Photoluminescence imaging of these samples at the wafer scale revealed concentric circular patterns, with higher recombination occurring in the centre, and far less around the periphery. Deep level transient spectroscopy measurements indicate the presence of recombination active defects, including a dominant center with an energy level at ∼Ev + 0.5 eV. Upon annealing FZ silicon at temperatures >1000 °C in oxygen, the lifetime is completely recovered, whereby the defects vanish and do not reappear upon subsequent annealing at 500 °C. We conclude that the heat‐treatments at >1000 °C result in total annihilation of the recombination active defects. Without such high temperature treatments, the minority carrier lifetime in FZ silicon is unstable and will affect the development of high efficiency (>24%) solar cells and surface passivation studies. This Letter demonstrates that commercially available float‐zone silicon wafers contain grown‐in vacancy defects, which cause very large instabilities in the bulk lifetime. This work offers a simple method to greatly improve the stability and lifetime of FZ silicon by permanently annihilating the vacancy defects through a high temperature >1000 °C anneal. The findings of this work are of particular interest for the development of very high efficiency solar cells and surface passivation studies.