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Summary: Insulator-to-Metal Transition in Sulfur-Doped Silicon
Mark T. Winkler,1
Daniel Recht,2
Meng-Ju Sher,1
Aurore J. Said,2
Eric Mazur,1,2
and Michael J. Aziz2
1
Department of Physics, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
2
School of Engineering and Applied Sciences, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138, USA
(Received 4 February 2011; revised manuscript received 1 April 2011; published 25 April 2011)
We observe an insulator-to-metal transition in crystalline silicon doped with sulfur to nonequilibrium
concentrations using ion implantation followed by pulsed-laser melting and rapid resolidification. This
insulator-to-metal transition is due to a dopant known to produce only deep levels at equilibrium
concentrations. Temperature-dependent conductivity and Hall effect measurements for temperatures
T > 1:7 K both indicate that a transition from insulating to metallic conduction occurs at a sulfur
concentration between 1.8 and 4:3 Â 1020 cmÀ3. Conduction in insulating samples is consistent with
variable-range hopping with a Coulomb gap. The capacity for deep states to effect metallic conduction by
delocalization is the only known route to bulk intermediate band photovoltaics in silicon.
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