Distribution of dislocations near the interface in AIN crystals grown on evaporated SiC substrates

To exploit unique properties of thin films of group III-nitride semiconductors, the production of native substrates is to be developed. The best choice would be AlN; however, presently available templates on sapphire or SiC substrates are defective. The quality of AlN could be improved by eliminating the substrate during the layer growth. In this paper, we demonstrate freestanding AlN layers fabricated by an SiC substrate evaporation method. Such layers were used to investigate dislocation structures near the former AlN?SiC interface. Specimens were characterized by synchrotron radiation imaging, triple-axis diffractometry and transmission electron microscopy (TEM). We found that the evaporation process under non-optimal conditions affected the dislocation structure. When the growth had been optimized, AlN layers showed a uniform distribution of dislocations. The dislocations tended to constitute low-angle subgrain boundaries, which produced out-of-plane and in-plane tilt angles of about 2?3 arc-min. Similar broadening was observed in both symmetric and asymmetric rocking curves, which proved the presence of edge, screws as well as mixed dislocation content. TEM revealed arrays of edge threading dislocations, but their predominance over the other threading dislocations was not supported by present study. To explain the experimental observations, a theoretical model of the dislocation structure formation is proposed. ? 2017 by the authors. Licensee MDPI, Basel, Switzerland.11Ysciescopu

Freestanding single crystal AlN layers grown using the SiC substrate evaporation method

The physical vapor transport growth of aluminium nitride (AlN) layers was performed in one process with the evaporation of silicon carbide (SiC) substrates. In this paper, we show that the rate of SiC evaporation is slow in a narrow process window for AlN growth but increases in the presence of AlN vapor. The properties of the substrates influence the evaporation process; therefore an investigation is done to understand this phenomenon. We first describe the evaporation behavior of a SiC substrate depending on its size, thickness, structure and polarity. Then we demonstrate the surface morphology and structural quality of the AlN layers grown on C-polar SiC. In the case of a step-flow growth, our method allows us to obtain thin freestanding layers with moderate dislocation densities and rocking curve widths comparable to those of bulk crystals. ? 2017 The Royal Society of Chemistry.11Nsciescopu

Effect of the Beryllium Acceptor Impurity upon the Optical Properties of Single-Crystal AlN

© 2020, Pleiades Publishing, Ltd. Abstract: 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

Magnetic properties of the natural and isotope-modified diamond and silicon carbide

The magnetic properties of single crystals of synthetic diamond and crystals of silicon carbide were studied. High-purity samples of diamonds synthesized with HPHT and CVD technologies were used. The crystals of silicon carbide were grown by sublimation and industrial technology. Along with samples with a natural isotopic composition, monoisotopic crystals of diamond (99.96% 12C and 99.96% 13C) and silicon carbide (99.993% of 28Si) were studied. On the basis of the data obtained, the diamagnetic susceptibility was determined and the concentration of paramagnetic centers and the content of the ferromagnetic component were evaluated. The results are discussed

Magnetic properties of the natural and isotope-modified diamond and silicon carbide

The magnetic properties of single crystals of synthetic diamond and crystals of silicon carbide were studied. High-purity samples of diamonds synthesized with HPHT and CVD technologies were used. The crystals of silicon carbide were grown by sublimation and industrial technology. Along with samples with a natural isotopic composition, monoisotopic crystals of diamond (99.96% 12C and 99.96% 13C) and silicon carbide (99.993% of 28Si) were studied. On the basis of the data obtained, the diamagnetic susceptibility was determined and the concentration of paramagnetic centers and the content of the ferromagnetic component were evaluated. The results are discussed

Thermal and lattice misfit stress relaxation in growing AIN crystal with simultaneous evaporation of SiC substrate

AlN single crystals were prevented from cracking by simultaneous growth and evaporation of SiC substrates. Freestanding layers (��1 mm thick) were proved continuous (non?cracked) and used as a model system to investigate the type of dislocation structure near AlN/SiC interface. Using x-ray diffraction techniques, we found that, unlike GaN films, in which high-density threading dislocations cross the film along its normal, the AlN layers possess a mosaic structure composed of low-angle subgrain boundaries. We suggest a theoretical model that describes the misfit stress relaxation in growing AlN crystal. ? 2017 Trans Tech Publications, Switzerland.11Nscopu

Microstructure and strength of AlN?SiC interface studied by synchrotron X-rays

Bulk AlN crystals grown by sublimation on SiC substrates exhibit relatively high dislocation densities. The kind of defect formation at early growth stages influences the structural quality of the grown crystals. In this work, the dislocation distribution near to the interface is understood through investigation of thin (��1.5?mm) continuous (non-cracked) freestanding crystals obtained in one process with the evaporation of the substrates. The AlN specimens were characterized using synchrotron radiation imaging techniques. We revealed by triple-axis X-ray diffraction study that, near to the former interface, randomly distributed dislocations configured to form boundaries between �� 0.02? misoriented sub-grains (from [0001] direction). Threading dislocation structure similar to that in epitaxial GaN films was not detected. To explain these observations, a theoretical model of misfit stress relaxation near the interface is suggested. ? 2016, Springer Science+Business Media New York.112sciescopu