Electrical compensation and cation vacancies in Al rich Si-doped AlGaN

We report positron annihilation results on vacancy defects in Si-doped Al0.90Ga0.10N alloys grown by metalorganic vapor phase epitaxy. By combining room temperature and temperature-dependent Doppler broadening measurements, we identify negatively charged in-grown cation vacancies in the concentration range from below 1 x 10 16 cm(-3) to 2 x 10 18 cm(-3) in samples with a high C content, strongly correlated with the Si doping level in the samples ranging from 1 x 10 17 cm(-3) to 7 x 10 18 cm(-3). On the other hand, we find predominantly neutral cation vacancies with concentrations above 5 x 10 18 cm(-3) in samples with a low C content. The cation vacancies are important as compensating centers only in material with a high C content at high Si doping levels.Peer reviewe

Europium diffusion in ammonothermal gallium nitride

Europium doping of gallium nitride using a novel ultra-high pressure annealing method was investigated. Ammonothermal gallium nitride substrates (n-type) were used as europium ion implantation targets using beam energy of 490 keV and ion fluences ranging from 1 x 1015 to 1 x 1016 Eu/cm2. The implanted samples were annealed at temperatures between 1473 K and 1753 K in high nitrogen pressure. Europium concentration profiles were analyzed along the [0001] crystallographic direction. The morphology and structural quality of implanted and annealed samples were examined. The "out-diffusion" phenomenon was noted. The presence of optically active EuGa-X defect complexes was suggested based on the analysis of photoluminescence spectra measured at low temperature (20 K). Limitations of diffusion-based europium doping of ammonothermal gallium nitride are discussed.Peer reviewe

AMINO ACIDS IDENTIFICATION IN THE HUMAN SKIN BY SPECTRA APPLICATION OF 0,05-1,2 THZ RANGE

Spectra of human skin and tableted preparations of amino acids in 0,05 1,2 THz range are obtained by terahertz spectroscopy method with time resolution. Comparison of the amino acids spectral lines is made for their identification in the skin. It is shown that the following amino acids are the most clearly visible in the skin spectrum: tryptophan, cysteine, alanine, glycine, phenylalanine and histidine. Terahertz spectral lines of the mentioned amino acids are associated with molecules oscillating modes, caused by chemical reactions, hydration processes and molecules conformal changes in the human skin. Determination of amino acids spectral lines and other specific molecules, involved in the metabolic processes of the skin, is necessary for the development of terahertz diagnostic tool with maximum sensitivity and selectivity