arXiv subjects

Francesca Chiodi

Publications and source records attributed to Francesca Chiodi.

4 recordsLinked to original sources

arXiv2026

Unlocking extreme doping and strain in epitaxial monocrystalline silicon

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.

cond-mat.mtrl-sci↗

arXiv2025

Structural and thermodynamic stability of hexagonal-diamond $\text{Si}_{1 - x - y}\,\text{Ge}_{x}\,\text{B}_{y}$ alloys

Pushing dopant concentrations beyond the solubility limit in semiconductors -- a process known as hyperdoping -- has been demonstrated as an effective strategy for inducing superconductivity in cubic-diamond Si and SiGe materials. Additionally, previous studies have reported that several polytypes of Si may exhibit a type-I superconducting state under high pressure. In this work, we employ ground-state Density Functional Theory simulations to investigate the effects of both low and high B doping concentrations on the structural and thermodynamic properties of hexagonal-diamond SiGe alloys, with a systematic comparison to their cubic-diamond counterparts. Our results highlight three key findings: (i) structural analysis confirms that the lattice parameters of SiGeB alloys adhere to a ternary Vegard's law, consistent with observations in cubic-diamond SiGe alloys. However, at high doping concentrations, B incorporation can locally disrupt the hexagonal symmetry, particularly in the presence of B clustering; (ii) dopant formation energy calculations reveal that B is thermodynamically more stable in the hexagonal phase than in the cubic phase across all Ge concentrations, regardless of the doping level; (iii) mixing enthalpy calculations demonstrate that hyperdoped hexagonal-diamond SiGe alloys are thermodynamically stable across the full range of Ge compositions and that their tendency for hyperdoping is more favorable than that of cubic-diamond SiGe alloys. Taken together, these findings indicate that hyperdoping is experimentally viable in hexagonal-diamond SiGe alloys and, in light of previous evidence, position these materials as a promising platform for the exploration of superconductivity in group IV semiconductors.

cond-mat.mtrl-sci↗

arXiv2022

Evidence of boron pairs in highly boron laser doped silicon

Secondary Ions Mass Spectroscopy and Hall effect measurements were performed on boron doped silicon with concentration between 0.02 at.% and 12 at.%. Ultra-high boron doping was made by saturating the chemisorption sites of a Si wafer with BCl3, followed by nanosecond laser anneal (Gas Immersion Laser Doping). The boron concentration varies thus nearly linearly with the number of process repetitions. However, it is not the case for the hole concentration which tends to saturate at high boron concentration. The difference between boron and hole concentration increases as the square of boron concentration, pointing towards the formation of boron pairs as the dominant contribution to the increase of inactive boron.

cond-mat.mtrl-sci↗

arXiv2015

Silicon Superconducting Quantum Interference Device

We have studied a Superconducting Quantum Interference SQUID device made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the Gas Immersion Laser Doping (GILD) technique. The SQUID device is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations.

cond-mat.mes-hall↗