Kovalenko T. Regularities of semiconductor diamond single crystals crystallization in growth systems with magnesium

The thesis for the degree of candidate of technical scienses, speciality 05.02.01 - Material Science. - V. Bakul Institute for Superhard Materials, NAS of Ukraine, Kyiv, 2017. The thesis is devoted to solution of important scientific and technical problem, which consists in developing a method of obtaining diamond single crystals in magnesium-based systems and establishing the regularities of the type IIb single crystals defect-impurity composition formation in Mg-C, Fe-Mg-C, Fe-Mg-Al-C systems depending on magnesium content and growth temperature. The features of diamond single crystals spontaneous crystallization in the Mg-C system at p = 7.0-8.5 GPa and T = 1350-2250 °С were studied. It was established that the linear growth rate increases with a temperature from ~100mkm/h at 1550-1600 °C to 3-5 mm/h at 2200 °C. The growth rate of the crystals on the seed at p = 7.7 GPa, T = 1950-2000 °C was: linear - 0.6-0.8 mm/h, mass - 24-38 mg/h. In the Fe-Mg-Al-C system an increase of magnesium amount leads to increasing of growth rates in 3 times for mass growth rates (from ~ 3 to 10 mg/h) and in ~2 times for linear growth rates (from 1.1 to 2.0 mm/h). Increasing magnesium content in the solvent >30 at. % leads to the type IIb single crystals formation. Type IIb crystals grown in magnesium-based systems possess semiconducting properties due to the presence in them of uncompensated boron impurity. Boron enters to the crystallization front from a carbon (graphite) source that contains an boron admixture in an amount of 10-5 wt. % without using other boron-containing additives. Keywords: crystallization, solution-melt system, single crystal, diamond, defect-impurity composition, magnesium, boron, silicon.