Growth method of GaN thin film on Si substrate and composite GaN thin film

A growth method of a GaN thin film on an Si substrate and a composite GaN thin film are disclosed. The composite GaN thin film comprises the Si substrate, an AlN buffering layer, a GaN buffering layer, a first GaN layer, an AlN inserting layer and a second GaN layer bottom up in sequence, wherein the GaN buffering layer comprises 2-3 three-dimensional and two-dimensional GaN sub layers; the thickness of the three-dimensional GaN sub layers is 50-150 nm; and the thickness of the two-dimensional GaN sub layers is 100-200 nm. The growth method comprises the following steps: firstly, growing the AlN buffering layer on the Si substrate, then growing the three-dimensional GaN sub layers on the AlN buffering layer, then growing the two-dimensional GaN sub layers, repeating the growth of the three-dimensional and two-dimensional sub layers of the GaN for 2-3 times; and finally growing thick GaN layer, wherein the AlN or the SiNx inserting layer is in the GaN layer. According to the growth method, by adoption of the three-dimensional and two-dimensional growth of the GaN, the ensile stress in the subsequent GaN layer is effectively relaxed off, so that thicker GaN layer can be produced without cracks.