Nitride-based semiconductor device and method for manufacturing thereof

A method for manufacturing a nitride-based semiconductor device, comprising:

• forming a first III-V nitride-based semiconductor layer over a substrate;
• forming a second III-V nitride-based semiconductor layer over the first III-V nitride-based semiconductor layer;
• forming a doped nitride-based semiconductor layer over the second III-V nitride-based semiconductor layer, wherein the doped nitride-based semiconductor layer has an aluminum concentration increasing along an upward direction;
• and
• forming a gate electrode on the doped nitride-based semiconductor layer.

A nitride-based semiconductor device comprising:

• a first III-V nitride-based semiconductor layer;
• a second III-V nitride-based semiconductor layer disposed over the first III-V nitride-based semiconductor layer and having a bandgap higher than a bandgap of the first III-V nitride-based semiconductor layer;
• and
• a doped nitride-based semiconductor layer disposed over the second III-V nitride-based semiconductor layer, wherein the doped nitride-based semiconductor layer has a bottom surface devoid of aluminum and a top surface comprising aluminum.