| 摘要 |
<p>When a substrate layer (desired semiconductor crystal) made of a group III nitride compound is grown on a base substrate comprising a lot of projection parts, a cavity in which a semiconductor crystal is not deposited may be formed between each projection part although it depends on conditions such as the size of each projection part, arranging interval between each projection part and crystal growth. So when the thickness of the substrate layer is sufficiently larger compared with the height of the projection part, inner stress or outer stress become easier to act intensively to the projection part. As a result, such stress especially functions as shearing stress toward the projection part. When the shearing stress becomes larger, the projection part is ruptured. So utilizing the shearing stress enables to separate the base substrate and the substrate layer easily. The larger the cavities are formed, the more stress tends to concentrate to the projection parts, to thereby enable to separate the base substrate and the substrate layer more securely. <??>A reaction prevention layer is formed to prevent Si from reacting with a gallium nitride group semiconductor. By forming a reaction prevention layer (monocrystalline material B) made of a material which has a higher melting point or thermal stability than that of a gallium nitride group semiconductor (semiconductor crystal A), e.g., SiC and AlN, on a base substrate (Si substrate), a reaction part described above is not formed around silicon interface when the gallium nitride group semiconductor (semiconductor crystal A) is grown by crystal growth for a long time. By forming a lot of projection parts, the gallium nitride group semiconductor (semiconductor crystal A) also grows in lateral direction starting from a flat-top portion of the projection part. Then stress between the reaction prevention layer and the semiconductor crystal A is remarkably relaxed. Because cracks which penetrate in longitudinal direction are hardly generated on the reaction prevention layer and the Si substrate can be completely interrupted by the reaction prevention layer, reaction preventing effect becomes more secure. <??>A seed layer comprising a GaN layer 103 (second seed layer) and an AlN buffer layer 102 (first seed layer) is formed on a sapphire substrate 101 and then the surface of the seed layer is etched in stripe pattern whose width of a stripe (width S of a seed) ≒ 5 mu m, width W of a wing ≒ 15 mu m and depth ≒ 0.5 mu m. Then mesas each of whose sectional form is a rectangular are formed, each erosion remains part having plural numbers of seed layers at its flat-top portion is formed at arrangement period L ≒ 20 mu m and a portion of the sapphire substrate 101 is exposed at the valley part of each wing. Preferably ratio of width of a seed toward a wing, or S/W, may be about 1/3. Then by growing the semiconductor crystal A to have thickness of 50 mu m or more and by separating it from base substrate, a single crystal of high quality which is independent from the base substrate is obtained. <IMAGE></p> |
