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We investigate the quenching of the photoluminescence (PL) from the divacancy defect in 4H-SiC consisting of a nearest-neighbour silicon and carbon vacancies. The quenching occurs only when the PL is excited below certain photon energies (thresholds), which differ for the four different inequivalent divacancy configurations in 4H-SiC. Accurate theoretical ab initio calculation for the charge-transfer levels of the divacancy show very good agreement between the position of the (0/−) level with respect to the conduction band for each divacancy configurations and the corresponding experimentally observed threshold, allowing us to associate the PL decay with conversion of the divacancy from neutral to negative charge state due to capture of electrons photoionized from other defects (traps) by the excitation. Electron paramagnetic resonance measurements are conducted in dark and under excitation similar to that used in the PL experiments and shed light on the possible origin of traps in the different samples. A simple model built on this concept agrees well with the experimentallyobserved decay curves.

We study the optical properties of tetravalent vanadium impurities in 4H silicon carbide (4H SiC). Emission from two crystalline sites is observed at wavelengths of 1.28 µm and 1.33 µm, with optical lifetimes of 163 ns and 43 ns. Group theory and ab initio density functional supercell calculations enable unequivocal site assignment and shed light on the spectral features of the defects. We conclude with a brief outlook on applications in quantum photonics. arXiv:1901.05371v2 [quant-ph]

Fluorescent paramagnetic defects in solids have become attractive systems for quantum information processing in the recent years. One of the leading contenders is the negatively charged nitrogen-vacancy defect in diamond with visible emission but alternative solution in technologically mature host is an immediate quest for many applications in this field. It has been recently found that various polytypes of silicon carbide (SiC), that are standard semiconductors with wafer scale technology, can host nitrogen-vacancy defect (NV) that could be an alternative qubit candidate with emission in the near infrared region. However, it is much less known about this defect than its counterpart in diamond. The inequivalent sites within a polytype and the polytype variations offer a family of NV defects. However, there is an insufficient knowledge on the magneto-optical properties of these configurations. Here we carry out density functional theory calculations, in order to characterize the numer ous forms of NV defects in the most common polytypes of SiC including 3C, 4H and 6H, and we also provide new experimental data in 4H SiC. Our calculations mediate the identification of individual NV qubits in SiC polytypes. In addition, we discuss the formation of NV defects in SiC with providing detailed ionization energies of NV defect in SiC which reveals the critical optical excitation energies for ionizing this qubits in SiC. Our calculations unravel the challenges to produce NV defects in SiC with a desirable spin bath.

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The divacancy in silicon carbide (SiC) is a prominent solid state defect quantum bit that bears a relatively strong fluorescence and optically detected magnetic resonance contrast (ODMR) at room temperature. These properties exemplify it for quantum sensing of biological molecules. To this end, we previously developed a top-down method to create divacancies in cubic SiC nanoparticles (NPs) as non-perturbative ODMR biomarkers. In this process, large SiC particles are synthesized and then stain etched to form porous SiC and then ultrasonication and filtering are applied to the solution to extract few nanometer diameter SiC NPs. We called this process no-photon exciton generation chemistry (NPEGEC). We showed that by adding aluminum to carbon and silicon in the synthesis process of cubic SiC, one can engineer divacancy defects in SiC NPs by NPEGEC. An alternative traditional way to introduce vacancies to the SiC lattice is irradiation. Here, we compare the fluorescence spectra of divacancies as created by neutron irradiation in porous cubic SiC and NPEGEC technique in SiC NPs, and the results are analyzed in detail by means of first principles calculations. We find that the irradiation technique produces a larger shift in the fluorescence spectrum with residual background fluorescence than that for divacancies in SiC NPs, which is most likely caused by the parasitic defects left after irradiation and annealing in the former sample. These results imply that the chemistry technique applied to prepare divacancies in few nanometer SiC NPs may preserve the bulk-like quality of divacancy quantum bits near the surface.