GaN Substrate and Method of Its Manufacture, Method of Manufacturing GaN Layer-Bonded Substrate, and Method of Manufacturing Semiconductor Device

The present invention makes available a GaN substrate, and a method of its manufacture, that, with minimal machining allowances, facilitates consistent machining, and makes available a method of manufacturing a GaN layer-bonded substrate, and a semiconductor device, utilizing the GaN substrate. A GaN substrate (20) of the present invention includes a first region (20j) and a second region (20i) that has a higher Ga/N atomic ratio than that of the first region (20j); wherein the second region (20i) widens from a depth D− D to a depth D+ D centered about a predetermined depth D from one major surface (20m), the difference between the Ga/N atomic ratio at the depth D and the Ga/N atomic ratio at a depth D+4 D or greater in the first region (20j) at the depth being three times the difference between the Ga/N atomic ratio at the depth D+ D and the Ga/N atomic ratio at the depth D+4 D or greater in the first region (20j), and wherein the ratio of the Ga/N atomic ratio in the second region (20i) to the Ga/N atomic ratio at the depth D+4 D or greater in the first region (20j) is at least 1.05.