Solid-state spin defects, characterized by their optical addressability and unique coherent properties, are garnering significant attention for their potential applications in quantum technologies, particularly as spin-photonic interfaces and highly sensitive sensors. This study investigates the long-term electron spin Rabi oscillations of nitrogen-vacancy (NV) centers embedded in a 6H-SiC crystal, stimulated by optical excitation at a wavelength of 980 nm. The experimental findings were acquired through pulsed electron paramagnetic resonance (EPR) conducted at a temperature of 150 K, utilizing two microwave (MW) frequency ranges: the X band (9.6 GHz) and the W band (94 GHz). The Rabi oscillation profiles were effectively modeled using a unified set of simulation parameters across varying MW pulse powers. A comparative analysis of the data from both MW frequency ranges revealed that the primary mechanism responsible for the damping of Rabi oscillations in the NV centers ensemble (with a concentration of CN = 1017cm-3) is attributed to the nonuniform distribution of the alternating magnetic field B1 within the EPR cavity. An analytical expression that accurately describes the experimentally observed increase in the modulation frequency of Rabi oscillations has been derived. The findings presented in this article are anticipated to contribute to the assessment of fidelity in various quantum algorithms that utilize the investigated spin systems as a foundational platform.

We have investigated the room temperature spin coherence properties of the axial NVkk center in 4H–SiC by pulsed high-frequency electron spin resonance and electron-nuclear double resonance techniques. Our results show a remarkable phase coherence time (TCoherence) of 25.3 μs at room temperature for ensembles of NV centers. We demonstrate precise control over NV defect spins through Rabi oscillations, which exhibit a linear response to microwave power. Additionally, the demonstrated room temperature readout of the intrinsic 14N nuclear spin (I = 1) underscores its potential as a robust nuclear spin memory resource, further positioning NV defects in 4H–SiC as an advanced platform for implementing cutting-edge quantum technologies in semiconductor systems.

NV- defects in silicon carbide (SiC) are emerging as a competitive alternative to NV- centers in diamond due to advanced industrial-scale SiC production methods. We present a study of the ground-state electron-nuclear coupling of negatively charged nitrogen-vacancy NV- centers in a 6H-SiC crystal by electron paramagnetic resonance and electron-nuclear double resonance techniques. The hyperfine and nuclear quadrupole interaction tensors have been precisely determined. The hyperfine coupling is found to be predominantly characterized by an isotropic contact Fermi part a(iso) = -1.125(2) MHz and a negligibly small dipole-dipole part b < 50 kHz. The nuclear quadrupole interaction is characterized by a coupling constant C-q = 2.530(3) MHz. The spin density distribution of the NVk2k1- center was calculated using density functional theory, and the theoretical electron-nuclear interaction values align well with experimental results. All established parameters are crucial for implementing NV- defects in SiC for quantum magnetometry, other sensing applications, and as robust qubits.

The high-temperature diffusion of an acceptor impurity of beryllium (Be) into bulk single-crystal aluminum nitride (AlN) has been studied. It is shown that the introduction of Be leads to the appearance of green luminescence of AlN, which is stable at room temperature and is observed over the entire thickness of the sample. It was shown by the method of luminescence analysis that the Be diffusion process is most efficiently realized in the temperature range from 1800 to 2100°C and is characterized by extremely high diffusion coefficients D = 10–7cm2/s and 10–6 cm2/s, respectively. It is shown that a prolonged diffusion process (t < 1 h) at a temperature of 2100°C leads to concentration quenching of the luminescence of near-surface AN layers with a thickness of ≈80 μm, which makes it possible to estimate the concentration of beryllium impurities in the near-surface layer on the order of ∼1019 cm–3.

The nitrogen-vacancy (NV) centers (NCVSi)− in 4H silicon carbide (SiC) constitute an ensemble of spin S = 1 solid state qubits interacting with the surrounding 14N and 29Si nuclei. As quantum applications based on a polarization transfer from the electron spin to the nuclei require the knowledge of the electron–nuclear interaction parameters, we have used high-frequency (94 GHz) electron–nuclear double resonance spectroscopy combined with first-principles density functional theory to investigate the hyperfine and nuclear quadrupole interactions of the basal and axial NV centers. We observed that the four inequivalent NV configurations (hk, kh, hh, and kk) exhibit different electron–nuclear interaction parameters, suggesting that each NV center may act as a separate optically addressable qubit. Finally, we rationalized the observed differences in terms of distinctions in the local atomic structures of the NV configurations. Thus, our results provide the basic knowledge for an extension of quantum protocols involving the 14N nuclear spin.

The question of why a high-quality bulk AlN crystal can be grown on a SiC seed, which is superior in a number of parameters to the same crystal grown on its own seed, remains open. We set ourselves the task of comprehensive analysis of the process of the formation of bulk AlN crystals on SiC using Raman spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy (EDXS), secondary ion mass spectroscopy (SIMS), and optical microscopy. We managed to detect silicon on the surface of the grown AlN сrystals and traces of silicon at the SiC/AlN phase boundary. In connection with this discovery, we consider a new model for the formation of high-quality bulk AlN crystal growth on SiC substrates through the formation of a layer of liquid silicon. The application of this model will facilitate the growth of large, high-quality AlN crystals.

The origns leading to the appearance of a green color of AlN crystals grown by sublimation on SiC seeds are investigated. It was shown by the method of secondary ion mass spectroscopy that the color of crystals weakly depends on the content of silicon and carbon, and a green or dark color appears only with an increased content of carbon in comparison with silicon. The presence of a separate amorphous carbon phase in these crystals was established by the method of Raman light scattering. The separation of the carbon phase in the process of crystal growth makes it difficult to obtain high-quality AlN crystals, as well as AlN-SiC solid solutions. The influence of growth conditions on the optical properties of AlN crystals is analyzed.

Controllable solid-state spin qubits are currently becoming useful building blocks for applied quantum technologies. Here, we demonstrate that in a specific type of silicon-vacancy in the 6H-SiC polytype the excited-state fine structure is inverted, compared to 4H-SiC. From the angular polarization dependencies of the emission, we reconstruct the spatial symmetry and determine the optical selection rules depending on the local deformation and spin–orbit interaction. We show that this system is well suited for the implementation of robust spin–photon entanglement schemes. Furthermore, the inverted fine structure leads to unexpected behavior of the spin readout contrast. It vanishes and recovers with lattice cooling due to two competing optical spin pumping mechanisms. Our experimental and theoretical approaches provide a deep insight into the optical and spin properties of atomic-scale qubits in SiC required for quantum communication and distributed quantum information processing.

The possibility of creating defects with spin-dependent fluorescence in a Van der Waals material, hexagonal boron nitride (hBN), by irradiating the latter with high-energy protons (E P =15 MeV) has been studied. Using micro-photoluminescence and electron paramagnetic resonance methods it was shown that such irradiation leads to the creation of boron vacancies in the negative charge state (V - B -centers). The ground spin triplet (S=1) state of these defects demonstrates an optically induced inverse population. Keywords: electron paramagnetic resonance, micro-photoluminescence, hexagonal boron nitride, boron vacancy.

We fabricate a quantum magnetic field sensor based on the silicon vacancy centers in 6H–SiC using atomic force microscopy technique. The quantum sensing is based on optically detected magnetic resonance. To implement quantum scanning microscopy, we attach a single 6H–SiC nanoparticle on the tip of the atomic force microscopy cantilever. Our quantum sensors are characterized using optical spectroscopy and electron microscopy. The use of such probes significantly reduces the cost of a quantum sensor and enables the extension of quantum scanning microscopes to physiological and conductive environments.

We report the influence of static mechanical deformation on the zero-field spin splitting of silicon vacancies in silicon carbide at room temperature. We use AlN/6H-SiC heterostructures deformed by growth conditions and monitor the stress distribution as a function of distance from the heterointerface with spatially resolved confocal Raman spectroscopy. The zero-field spin splitting of the V1/V3 and V2 centers in 6H-SiC, measured by optically detected magnetic resonance, reveals significant changes at the heterointerface compared to the bulk value. This approach allows unambiguous determination of the spin-deformation interaction constant, which is 0.75 GHz/strain for the V1/V3 centers and 0.5 GHz/strain for the V2 centers. Provided piezoelectricity of AlN, our results offer a strategy to realize fine tuning of spin transition energies in SiC by deformation.

The effect of static mechanical strain on the splitting of spin sublevels of color centers based on spin 3/2 silicon vacancies in silicon carbide at room temperature has been shown. The deformed heterointerface of the AlN/4H-SiC structure has been studied. Stresses near the heterointerface have been determined using confocal Raman spectroscopy. The spin–strain coupling constants $$\Xi = ( - 0.1 \pm 0.25)$$ GHz/strain and $$\Xi {\kern 1pt} ' = ( - 0.8 \pm 0.1)$$ GHz/strain for the V2 center in 4H-SiC have been experimentally determined for the first time using the optically detected magnetic resonance method. The results obtained can be used to control spin states in SiC by means of the controlled piezoelectric strain in AlN and to estimate the fine-structure parameter D of spin centers using Raman scattering. Such an estimate makes it possible to forecast magnetometric parameters of nanosensors based on SiC nanocrystals.

Thermal conductivity κ(T) of single crystal aluminum nitride grown by physical vapor transport has been measured at temperatures T from 5 to 410 K. The samples exhibit high thermal conductivity with a value of up to 316 W m−1 K−1 at room temperature and about 2800 W m−1 K−1 at a peak of 66 K. At lowest temperatures, κ(T) approaches the conductivity limited by the diffuse phonon scattering from sample surfaces. The peculiarities in measured κ(T) suggest that the phonon scattering from point defects contributes essentially to the total phonon scattering in samples under investigation at low temperatures. The phonon interaction with electrons and holes bound to neutral donor and acceptor centers is suggested, adding substantially to thermal resistivity near and below the peak in κ(T).

The influence of the high-temperature ( T = 1880°C) diffusion of beryllium ions on the properties of single-crystal aluminum nitride is studied. It is shown that the postgrowth doping of AlN with Be brings about the compensation of shallow Si donor centers uncontrollably incorporated into the AlN lattice during growth. It is established that the introduction of Be into the AlN lattice results in a reduction in the optical absorption of AlN in the visible and ultraviolet regions. The set of results is attributed to a shift of the Fermi level to the top of the valence band of AlN upon the introduction of the Be acceptor impurity.

A new diagnostic method for evaluation of the local polytypic composition of silicon carbide at room temperature is proposed using known and tabulated zero-field splitting values for spin color centers with S=3/2 whose frequency parameters are in the megahertz range and depend on the specific polytype. The zero-field splitting values are recorded from the change in the photoluminescence in the near infrared, either under the optically detected magnetic resonance conditions or under the level anticrossing conditions of the spin centers. The proposed method can be used to identify silicon carbide known as carborundum in nature by recording optically induced radio frequency emission of spin color centers, including outer space.

Boron, aluminum, and nitrogen are major and critical elements in silicon carbide. The concentrations of these elements influence the electrical properties of silicon carbide and also the generation of defects. Purification was executed in the powder manufacturing process. High purity powder was used to grow the crystal, which was then sliced into wafers in this work. Secondary ion mass spectroscopy (SIMS) and glow discharge mass spectrometry (GDMS) were used to measure boron, aluminum, and nitrogen concentrations in wafer and powder to compare the concentration difference. The concentration of the elements varies depending on the element’s physical property. Transfer coefficient is defined as the ratio of element concentration in wafer to powder, which is interesting to realize the element behavior in PVT process and studied in this work.

Terahertz electroluminescence of unipolar n⁺⁺-n⁻-n⁺ SiC structures at helium temperatures and I-V characteristics of bipolar n⁺⁺-π-n⁺ SiC structures with natural superlattices at 300~K at strong electrical fields are studied. The properties of the THz electroluminescence and I-V characteristics testify that these phenomena due to Bloch oscillations.

We review the history and modern state of silicon carbide and SiC-based devices. The main techniques for growing bulk SiC crystals and epitaxial SiC films are discussed. Epitaxial SiC structures used for post-growth processing are briefly reviewed. The state of the art achieved in developing SiC devices is presented. The main problems that occur in developing SiC equipment and prospects for designing and developing such equipment are analyzed.

We report on co-doping of high-quality AlN single crystals by group II Beryllium acceptors by means of diffusion from the vapour phase at a temperature of 1850 °C. We discovered that Be is characterized by the high diffusion length, allowing one to produce Be co-doping of sub-mm-thick AlN wafers. We show that Be diffusion led to the quenching of the visible (VIS) 450 nm (2.75 eV) and deep ultraviolet (UV) 265 nm (4.7 eV) optical absorption bands with simultaneous induction of the absorption band peaked at 248 nm (5 eV). By means of electron paramagnetic resonance (EPR), we also found that the presence of Be impurities compensated the donor type paramagnetic centers. Correlation of the EPR data with the optical absorption allowed us to conclude that Be produced in the AlN via diffusion acted predominantly as an acceptor, inducing the shift of the Fermi level to the lower part of the AlN bandgap. This shift of the Fermi level results in recharging of the deep level defects in the AlN bandgap, which explains the observed quenching of the VIS and UV absorption bands.

Results of the study of the terahertz electroluminescence from 8H-, 6H- and 4H-SiC natural superlattices (NSL) under action of strong electrical field applied along the natural superlattice axis are reported. It is shown that the threshold field of the appearance of THz BO emission and the threshold field for the negative differential conductivity for these SiC NSLs increase linearly with the width of the first miniband of these NSLs. This observation is a crucial factor in support of the BO nature of the terahertz electroluminescence and the negative differential conductivity for these SiC NSLs.