Insulator-to-metal transition in sulfur-doped silicon

TL;DR

This paper reports the observation of an insulator-to-metal transition in sulfur-doped silicon at high dopant concentrations, demonstrating a potential route for intermediate band photovoltaics.

Contribution

It provides experimental evidence of a metal transition in silicon doped with deep-level sulfur, achieved through ion implantation and pulsed laser melting.

Findings

Transition occurs at sulfur concentration between 1.8 and 4.3 x 10^20 cm-3

Insulating samples show variable range hopping conduction

Deep states can induce metallic conduction via delocalization

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 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 x 10^20 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.