High electron mobility transistor epitaxial structure that includes carbon doped nitride layers

A high electron mobility transistor epitaxial structure, comprising:

• a substrate;
• a nucleation layer located above the substrate;
• a buffer layer located above the nucleation layer;
• a first nitride layer located above the buffer layer and being in contact with the buffer layer;
• a second nitride layer located above the first nitride layer and being in contact with the first nitride layer, wherein a film thickness of the first nitride layer is less than a film thickness of the second nitride layer;
• the second nitride layer is carbon doped, wherein a carbon concentration of the first nitride layer is less than a carbon concentration of the second nitride layer;
• a channel layer located above the second nitride layer;
• and
• a barrier layer, wherein a two-dimensional electron gas is formed in the channel layer along an interface between the channel layer and the barrier layer,
• wherein a ratio of the carbon concentration of the second nitride layer to the carbon concentration of the first nitride layer is greater than or equal to 10, and
• wherein the buffer layer is made of aluminum-gallium nitride (AlGaN) and has a surface aluminum (Al) concentration of 25%±10%.