Abstract: An object of the present invention is to provide, even when a single crystal of a material other than AlN is used as a crystal, an AlN bulk single crystal having fewer defects and high quality, a method for producing such an AlN bulk single crystal, and a semiconductor device. A feature is to select, as a surface 1a of a hexagonal single crystal substrate serving as a seed crystal 1, a plane inclined at an angle of 10° to 80° with respect to the C-plane (FIG. 1(a)), and to grow an AlN single crystal 2 as a growth plane 2a on the surface 1a by a sublimation method (FIG. 1(b)).

Abstract: This invention concerns a process for purifying silica produced from an alkali silicate aqueous solution, which usually contains more than 200 ppm of impurities, to silica containing less than 30 ppm of impurities. Concretely, the purification process of silica comprises: dispersing silica gel, containing a lot of impurities, in water and filtering the solution; dispersing the filtered out silica gel again in an aqueous solution of pH 2 or less and filtering the aqueous solution; putting the silica gel to heat-treatment and acid-treatment with continuous stirring in order to break the inside siloxane link and dissolve out impurities therefrom and filtering the acid solution; rinsing a produced cake with pure water to wash away the inside residual solution and drying the cake.