Insulator-to-metal transition in sulfur-doped silicon

Abstract:

We observe an insulator-to-metal (I–M) transition in crystalline silicon doped with sulfur to non-equilibrium concentrations using ion implantation followed by pulsed laser melting and rapid resolidification. This I–M transition is due to a dopant known to produce only deep levels at equilibrium concentrations. Temperature-dependent conductivity and Hall effect data measured for temperatures T > 1.7 K both indicate that a transition from insulating to metallic conduction occurs at a peak sulfur concentration between 1.8 and 4.3 × 1020 cm–3. 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.