Breaking the doping limit in silicon by deep impurities

TL;DR

This paper demonstrates that doping silicon with deep impurities like tellurium via non-equilibrium processing can surpass the traditional doping limits of shallow impurities, achieving higher electron concentrations and inducing an insulator-to-metal transition.

Contribution

It introduces a novel doping method using deep impurities, specifically tellurium, to exceed the Fermi-level pinning limit in silicon, supported by first-principles calculations.

Findings

Deep Te doping exceeds traditional doping limits in Si.

Te dimers act as effective donors with lowest formation energy.

Achieves non-saturating carrier concentration and insulator-metal transition.

Abstract

N-type doping in Si by shallow impurities, such as P, As and Sb, exhibits an intrinsic limit due to the Fermi-level pinning via defect complexes at high doping concentrations. Here we demonstrate that doping Si with the chalcogen Te by non-equilibrium processing, a deep double donor, can exceed this limit and yield higher electron concentrations. In contrast to shallow impurities, both the interstitial Te fraction decreases with increasing doping concentration and substitutional Te dimers become the dominant configuration as effective donors, leading to a non-saturating carrier concentration as well as to an insulator-to-metal transition. First-principle calculations reveal that the Te dimers possess the lowest formation energy and donate two electrons per dimer to the conduction band. These results provide novel insight into physics of deep impurities and lead to a possible solution for the ultra-high electron concentration needed in today's Si-based nanoelectronics.