Semiconductor device and method of manufacturing the same

A semiconductor device comprising:

• a channel layer;
• a lower barrier layer on the channel layer and comprising first impurities;
• an upper barrier layer on the lower barrier layer and comprising second impurities having a concentration greater than a concentration of the first impurities;
• a gate electrode on the upper barrier layer;
• a gate semiconductor layer between the upper barrier layer and the gate electrode;
• and
• a source and a drain that are on the channel layer and are spaced apart from each other,
• wherein the lower barrier layer defines a recess, and a thickness of a portion of the lower barrier layer that is close to the gate electrode is less than a thickness of an edge portion of the lower barrier layer.

A method of manufacturing a semiconductor device, the method comprising:

• sequentially forming a channel layer, a lower barrier layer, an upper barrier layer, and a gate semiconductor layer on a substrate;
• etching the upper barrier layer and the gate semiconductor layer;
• forming a gate electrode on the gate semiconductor layer;
• and
• forming a source and a drain respectively being in contact with a first side of and a second side of the channel layer,
• wherein the forming of the lower barrier layer and the upper barrier layer comprises making a concentration of a second impurity in the upper barrier layer be greater than a concentration of a first impurity in the lower barrier layer.