Unlocking extreme doping and strain in epitaxial monocrystalline silicon

TL;DR

This paper demonstrates a novel laser doping technique in epitaxial silicon that achieves record dopant concentrations and lattice deformations, supported by a simple combinatorial model and first-principles calculations.

Contribution

It introduces a new laser doping method for epitaxial silicon that enables extreme hyperdoping levels and provides a theoretical framework to understand the doping limitations.

Findings

Achieved 8% carrier concentration in silicon.

Recorded 3% lattice deformation.

Developed a combinatorial model explaining doping limits.

Abstract

Hyperdoping, overcoming the solubility limit of dopants in a crystalline semiconductor, is a fertile method for the enhancement of the electrical, structural and optical devices' performances and for the exploration of exotic phases such as superconductivity. We demonstrate an unprecedented control on the dopant concentration and lattice deformation via nanosecond laser doping in epitaxial boron doped silicon, achieving record carrier concentrations (8 at.%) and lattice deformations (3 %). Probing the microscopical hyperdoping limitations, we show that the relevant mechanisms are caught by a simple combinatorial model, which quantitatively explains both the experimental carrier concentration and lattice deformation evolution. First principle calculations complete and support such simple model. Indeed, at the high doping levels now attainable, the maximum carrier concentration is inherently limited by the probability of two or three substitutional dopants occupying neighboring lattice sites, forming partially inactive complexes that we detail. This description is valid in the case of perfect layers with no crystallographic defects and a fully substitutional dopant occupation, highlighting the quality of the epitaxial layers realized.