Composite substrate and manufacturing method thereof

A method of manufacturing a composite substrate, comprising:

• providing a first silicon-containing layer comprising a plurality of group V atoms;
• performing a first heat treatment to the first silicon-containing layer;
• providing a substrate having an insulation layer;
• disposing the first silicon-containing layer on the insulation layer;
• performing a thinning process on the first silicon-containing layer to obtain a thinned first silicon-containing layer comprising a first surface and a second surface opposite to the first surface, and the second surface being in direct contact with the insulation layer, wherein a distribution concentration of the plurality of group V atoms from the second surface to the first surface gradually increases;
• and
• performing a first epitaxial process comprising simultaneously:
• forming a first epitaxial layer including a plurality of group III atoms on the thinned first silicon-containing layer;
• and
• performing a second heat treatment so that a distribution concentration of the plurality of group III atoms increases as getting closer to the thinned first silicon-containing layer to obtain a composite substrate.