Semiconductor device and method for fabricating the same

A semiconductor device comprising:

• a first nitride semiconductor layer;
• a second nitride semiconductor layer formed on the first nitride semiconductor layer and having such a composition as to generate a 2-dimensional electron gas layer in an upper portion of the first nitride semiconductor layer;
• and
• an ohmic electrode formed selectively on the second nitride semiconductor layer, wherein the second nitride semiconductor layer has a contact area defining a depressed cross-sectional configuration,
• the contact area has a bottom portion containing an impurity having a conductivity introduced therein and a sidewall composed of an insulating film on an inner wall surface thereof, and
• the ohmic electrode is formed to cover an inner side of the contact area including the sidewall.

A semiconductor device comprising:

• a first nitride semiconductor layer;
• a second nitride semiconductor layer formed on the first nitride semiconductor layer and having such a composition as to generate a 2-dimensional electron gas layer in an upper portion of the first nitride semiconductor layer;
• a third nitride semiconductor layer formed on the second nitride semiconductor layer and smaller in band gap energy than the second nitride semiconductor layer;
• and
• an ohmic electrode formed selectively on the third nitride semiconductor layer, wherein
• the third nitride semiconductor layer includes a contact area having at least one inclined surface which is inclined toward an upper surface of the second nitride semiconductor layer and defining a depressed cross-sectional configuration and
• the ohmic electrode is formed on the contact area.