arXiv subjects

Joel Davidsson

Publications and source records attributed to Joel Davidsson.

23 records · Page 2Linked to original sources

arXiv2021

ADAQ: Automatic workflows for magneto-optical properties of point defects in semiconductors

Automatic Defect Analysis and Qualification (ADAQ) is a collection of automatic workflows developed for high-throughput simulations of magneto-optical properties of point defect in semiconductors. These workflows handle the vast number of defects by automating the processes to relax the unit cell of the host material, construct supercells, create point defect clusters, and execute calculations in both the electronic ground and excited states. The main outputs are the magneto-optical properties which include zero-phonon lines, zero-field splitting, and hyperfine coupling parameters. In addition, the formation energies are calculated. We demonstrate the capability of ADAQ by performing a complete characterization of the silicon vacancy in silicon carbide in the polytype 4H (4H-SiC).

cond-mat.mtrl-sci↗

arXiv2020

Theoretical polarization of zero phonon lines in point defects

In quantum technologies, point defects in semiconductors are becoming more significant. Understanding the frequency, intensity, and polarization of the zero phonon line is important. The last two properties are the subject of this paper. I present a method for calculating these properties and show the importance of using wave functions from both the ground and excited state. The validity of this method is demonstrated on the divacancy in 4H-SiC. Here, the calculated polarization and lifetimes are in excellent agreement with experimental measurements. In general, this method can help to identify point defects and estimate suitable applications.

cond-mat.mtrl-sci↗

arXiv2019

Semi-Local Parameterization of the Electron Localization Function in Second-Order Density Gradients

The electron localization function (ELF) is a universal measure of electron localization that allows for, e.g., an effective characterization of physical bonds in molecular and solid state systems. In the context of the widely used Kohn-Sham density-functional theory (KS-DFT) and its generalizations, ELF is given in terms of the single-particle electron density as well as the non-interacting kinetic energy density (KED) of the KS system. Starting from the notion of an edge electron gas put forth by Kohn and Mattsson, we here use an \emph{exactly soluble}, strongly correlated few-electron model of a harmonically confined electron gas in order to parameterize the positive-definite non-interacting KS KED in terms of the density and its reduced second-order gradients. We arrive at a simple, yet generally applicable functional approximation to ELF expressed in the electron density and its derivatives. To demonstrate the validity of our approach, we use the obtained parameterization to perform topological analysis of the bonds in solid Al and Si, and to study physical and chemical adsorption of graphene on a Ni surface. We find that while the expression does not provide a quantitatively accurate approximation of absolute ELF values, the most essential qualitative features are captured. Hence, the expression is useful in contexts where the electron density is available, but not the KS orbitals or the KED, and one desires a qualitative picture of the electron localization that mimics ELF.

cond-mat.str-el↗

arXiv2017

Identification of Si-vacancy related room temperature qubits in 4H silicon carbide

Identification of microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, silicon vacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin-3/2 ground and excited states. Although, these centers were observed decades ago, still two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] are argued as an origin. By means of high precision first principles calculations and high resolution electron spin resonance measurements, we here unambiguously identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Si-vacancy qubit configurations that provide room temperature optical readout.

cond-mat.mtrl-sci↗

arXiv2017

First principles predictions of magneto-optical data for semiconductor defects: the case of divacancy defects in 4H-SiC

Study and design of magneto-optically active single point defects in semiconductors are rapidly growing fields due to their potential in quantum bit and single photon emitter applications. Detailed understanding of the properties of candidate defects is essential for these applications, and requires the identification of the defects microscopic configuration and electronic structure. Multi-component semiconductors often host two or more non-equivalent configurations of point defects. These configurations generally exhibit similar electronic structure and basic functionalities, however, they differ in details that are of great importance whenever single defect applications are considered. Identification of non-equivalent configurations of point defects is thus essential for successful single defect manipulation and application. A promising way to identify defects is via comparison of experimental measurements and results of first-principle calculations. We investigate a possibility to produce accurate ab initio data for zero-phonon lines and hyperfine coupling parameters that are required for systematic quantum bit search. We focus on properties relevant for the possible use of the divacancy defect in quantum bits in 4H-SiC. We provide a decisive identification of divacancy configurations in 4H-SiC and clarify differences in prior predictions of 4H-SiC divacancy zero-phonon photoluminescence lines.

cond-mat.mtrl-sci↗