Abstract: A semiconductor substrate inclu8des an AlN layer that is formed so as to contact a Si substrate and has an FWMH of a rocking curve of a (002) plane by x-ray diffraction, the FWMH being less than or equal to 1500 seconds, and a GaN-based semiconductor layer formed on the AlN layer.

Abstract: A method for fabricating a semiconductor device includes forming an AlN layer on a substrate made of silicon by supplying an Al source without supplying a N source and then supplying both the Al source and the N source, and forming a GaN-based semiconductor layer on the AlN layer after the forming of the AlN layer. The forming of the AlN layer grows the AlN layer so as to satisfy the following: 76500/x0.81y<53800/x0.83 where x is a thickness of the AlN layer and y is an FWHM of a rocking curve of a (002) plane of the AlN layer.

Abstract: A method for fabricating a semiconductor device including: cleaning an apparatus used to grow a layer including Ga; performing a first step of forming a first layer on a substrate made of silicon by using the apparatus, the first layer including a nitride semiconductor that does not include Ga as a composition element and has a Ga impurity concentration of 2×1018 atoms/cm3 or less; and performing a second step of forming a second layer on the first layer by using the apparatus after the first step is repeatedly carried out multiple times, the second layer including a nitride semiconductor including Ga.

Abstract: A method for fabricating a semiconductor device including: cleaning an apparatus used to grow a layer including Ga; performing a first step of forming a first layer on a substrate made of silicon by using the apparatus, the first layer including a nitride semiconductor that does not include Ga as a composition element and has a Ga impurity concentration of 2×1018 atoms/cm3 or less; and performing a second step of forming a second layer on the first layer by using the apparatus after the first step is repeatedly carried out multiple times, the second layer including a nitride semiconductor including Ga.

Abstract: A semiconductor device includes a substrate, a superlattice buffer layer that is formed on the substrate and is composed of first AlxGa1-xN layers and second AlxGa1-xN layers having an Al composition greater than that of the first AlxGa1-xN layers, the first and second AlxGa1-xN layers being alternately stacked one by one, both the Al compositions of the first and second AlxGa1-xN layers being greater than 0.3, and a difference in Al composition between the first and second AlxGa1-xN layers being greater than 0 and smaller than 0.6.

Abstract: A semiconductor substrate includes: an AlN layer provided on a silicon substrate; an AlGaN layer that is provided on the AlN layer and has an Al composition ratio of 0.3 to 0.6; and a GaN layer provided on the AlGaN layer.