Bálint Somogyi

Transition Metal Defects in Cubic and Hexagonal Polytypes of SiC: Site Selection, Magnetic and Optical Properties from Ab Initio Calculations

Relatively little is known about the transition metal defects in silicon carbide (SiC). In this study we applied highly convergent and sophisticated density functional theory (DFT) based methods to investigate important transition metal impurities including titanium (Ti), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo) and tungsten (W) in cubic 3C and hexagonal 4H and 6H polytypes of SiC. We found two classes among the considered transition metal impurities: Ti, V and Cr clearly prefer the Si-substituting configuration while W, Nb, and Mo may fractionally form a complex with carbon vacancy in hexagonal SiC even under thermal equilibrium. If the metal impurity is implanted into SiC or when many carbon impurities exist during the growth of SiC then complex formation between Si-substituting metal impurity and the carbon vacancy should be considered. This complex pair configuration exclusively prefers the hexagonal-hexagonal sites in hexagonal polytypes and may be absent in cubic polytype. We also studied transition metal doped nano 3C-SiC crystals in order to check the effect of the crystal field on the d-orbitals of the metal impurity.

Photoluminescence, infrared, and Raman spectra of co-doped Si nanoparticles from first principles

Co-doped silicon nanoparticles (NPs) are promising for the realization of novel biological and optoelectronic applications. Despite the scientific and technological interest, the structure of heavily co-doped Si NPs is still not very well understood. By means of first principles simulations, various spectroscopic quantities can be computed and compared to the corresponding experimental data. In this paper, we demonstrate that the calculated infrared spectra, photoluminescence spectra, and Raman spectra can provide valuable insights into the atomistic structure of co-doped Si NPs.

Introducing Color Centers to Silicon Carbide Nanocrystals for In Vivo Biomarker Applications: A First Principles Study

Molecule-sized fluorescent emitters are much sought-after to probe biomolecules in living cells. We demonstrate here by time-dependent density functional calculations that the experimentally achievable 1-2 nm sized silicon carbide nanocrystals can emit light in the nearinfrared region after introducing appropriate color centers in them. These near-infrared luminescent silicon carbide nanocrystals may act as ideal fluorophores for in vivo bioimaging.