Semiconductor device and fabrication method thereof

A method of fabricating a semiconductor device, comprising:

• providing a semiconductor substrate;
• forming a layer stack structure over the semiconductor substrate, the layer stack structure includes a channel layer, a gate dielectric layer and a gate layer sequentially stacked over one another;
• patterning the layer stack structure to form a gate structure;
• and
• forming source and drain terminals over the channel layer, the source and drain terminals being in contact with the channel layer, wherein the channel layer includes a scandium-doped aluminum oxycarbide layer, the gate dielectric layer includes a scandium-doped aluminum nitride layer and the gate layer includes a scandium-doped aluminum layer, a scandium content in the channel layer gradually varies from a first side of the channel layer to a second side of the channel layer, and wherein top surfaces of the source and drain terminals are located at a position higher than a topmost interface of the gate dielectric layer and the channel layer.