ИСТИНА

As a result of ZnO hydrothermal synthesis, a reliable crystal growth technology is developed. Transparent, light yellow–green color zincite single crystals with size up to 2 inches were obtained. A method of defect–selective etching is suggested to study the real structure of ZnO material. It was found that aqueous solutions of 25 mole% HCl + 3 mole% NH4F seem to be the best media for selective etching and possess to reveal linear violations of crystal structure. Further investigations revealed two kind of etch pits which correspond to two different types of defects. Dislocation density depends on the defect quantity in seed slices as well as on growth conditions. High supersaturation, solid inclusions and unstable growth conditions lead to increase in number of structural defects. It was shown that usage of “turning” seed slices possesses to grow ZnO single crystal with low dislocation density. As a result, ZnO single crystals with low dislocation density, thickness up to 12 mm and weight of about 150 g have been grown on “turning” seed slices. A minor concentration of iron impurities (less than 0.04 at %) was observed in ZnO crystals. Hydrothermally grown ZnO crystals are stable in vacuum, argon, nitrogen and oxygen up to 1050oC under 4-hour thermal treatment, but not higher 650-700oC in the case of the hydrogen atmosphere. Several substrates of 10x10 mm2 were fabricated for the first stage of experiments on GaN epitaxy. The substrates were characterized and estimates of the defect density, through measurement of he high-resolution x-ray linewidths developed.The results obtained have crucial scientific importance for the commercialization of both wide band gap distinguished materials, ZnO bulk crystals and Ga-nitride thin films, in the USA as well as in Russia.