Thermal conductivity $\kappa (T)$ 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, $\kappa (T)$ approaches the conductivity limited by the diffuse phonon scattering from sample surfaces. The peculiarities in measured $\kappa (T)$ 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 $\kappa (T)$ .

Quantum technologies are currently being explored for various applications, including computing, secure communication, and sensor technology. A critical aspect of achieving high-fidelity spin manipulations in quantum devices is the controlled optical initialization of electron spins. This paper introduces a low-cost programming scheme based on a 32-bit STM32F373 microcontroller, aimed at facilitating high-precision measurements of optically active solid-state spin centers within semiconductor crystals (SiC, hBN, and diamond) utilizing a multi-pulse sequence. The effective shaping of short optical pulses across semiconductor and solid-state lasers, covering the visible to near-infrared range (405–1064 nm), has been validated through photoinduced electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopies. The application of pulsed laser irradiation influences the EPR relaxation parameters associated with spin centers, which are crucial for advancements in quantum computing. The presented experimental approach facilitates the investigation of weak electron–nuclear interactions in crystals, a key factor in the development of quantum memory utilizing nuclear qubits.

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.

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.

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^oC and is characterized by extremely high diffusion coefficients D=10^-7 cm²/s and 10^-6 cm²/s, respectively. It is shown that a prolonged diffusion process (t≤1 hour) at a temperature of 2100^oC leads to concentration quenching of the luminescence of near-surface AlN 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. Keywords: AlN PVT doping diffusion.