Letter abstract
Nature Materials 4, 680 - 684 (2005)
doi:10.1038/nmat1458
Subject Categories: Metals and alloys | Semiconductors
A density-driven phase transition between semiconducting and metallic polyamorphs of silicon
Paul F. McMillan1,2, Mark Wilson1, Dominik Daisenberger1 and Denis Machon1
Amorphous and crystalline forms of silicon are well-known, tetrahedrally coordinated semiconductors. High-pressure studies have revealed extensive polymorphism among various metallic crystal structures containing atoms in six-, eight- and 12-fold coordination1, 2. Melting silicon at ambient or high pressure results in a conducting liquid, in which the average coordination is greater than four (ref. 3). This liquid cannot normally be quenched to a glass, because of rapid crystallization to the diamond-structured semiconductor4. Solid amorphous silicon is obtained by synthesis routes such as chemical or physical vapour deposition that result in a tetrahedrally bonded semiconducting state. It has long been speculated that the amorphous solid and the liquid could represent two polymorphic forms of the amorphous state that are linked by density- or entropy-driven transformations5, 6, 7, 8. Such polyamorphic transitions are recognized to occur among several different types of liquid and glassy systems9, 10, 11, 12, 13, 14. Here we present experimental evidence for the occurrence of a density-driven polyamorphic transition between semiconducting and metallic forms of solid amorphous silicon. The experiments are combined with molecular dynamics simulations that map the behaviour of the amorphous solid on to that of the liquid state.
- Department of Chemistry and Materials Chemistry Centre, Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ, UK
- Davy-Faraday Research Laboratory, Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS, UK
Correspondence to: Paul F. McMillan1,2 e-mail: p.f.mcmillan@ucl.ac.uk
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