Abstract: A carbon-fiber-reinforced silicon-carbide-based composite material which has better strength and toughness, and a braking material, such as a brake disc using the composite material, are provided. By using the carbon-fiber-reinforced silicon-carbide-based composite material including a bundle of fibers having chopped carbon fibers arranged in parallel and the other carbon component, carbon, silicon, and silicon carbide, in which the fiber bundle is flat, its cross-section perpendicular to its longitudinal direction has a larger diameter of 1 mm or more, a ratio of the larger diameter to a smaller diameter is from 1.5 to 5, and a plurality of the fiber bundles are randomly oriented substantially along a two-dimensional plane, and a two-dimensional side serves as a braking side to thereby constitute the braking material.

Abstract: A nitride semiconductor substrate is provided in which leak current reduction and improvement in current collapse are effectively attained when using Si single crystal as a base substrate. The nitride semiconductor substrate is such that an active layer of a nitride semiconductor is formed on one principal plane of a Si single crystal substrate through a plurality of buffer layers made of a nitride, in the buffer layers, a carbon concentration of a layer which is in contact with at least the active layer is from 1×1018 to 1×1020 atoms/cm3, a ratio of a screw dislocation density to the total dislocation density is from 0.15 to 0.3 in an interface region between the buffer layer and the active layer, and the total dislocation density in the interface region is 15×109 cm?2 or less.