Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device comprising:

• forming a buffer layer made of a nitride semiconductor;
• forming a channel layer made of a nitride semiconductor over the buffer layer;
• forming a barrier layer made of a nitride semiconductor over the channel layer;
• a cap layer made of a nitride semiconductor formed the barrier layer;
• forming a gate insulating film so as to be in contact with the cap layer;
• and
• forming a gate electrode over the gate insulating film,
• wherein the cap layer, the barrier layer, the channel layer, and the buffer layer are polarized;
• wherein negative charge is higher than positive charge at an interface between the cap layer and the barrier layer and an interface between the channel layer and the buffer layer and positive charge is higher than negative charge at an interface between the barrier layer and the channel layer by controlling compositions of the cap layer, the barrier layer, the channel layer, and the buffer layer;
• wherein the channel layer has a stacked layer structure of a first layer, a second layer, and a third layer;
• and
• wherein the second layer has a higher electron affinity than those of the first layer and the third layer by controlling compositions of the first layer, the second layer, and the third layer.

A method for manufacturing a semiconductor device comprising:

• forming a buffer layer made of AlxGa1-xN;
• forming a channel layer having a stacked layer structure stacking a GaN layer, an InyGa1-yN layer, and a GaN layer in this order over the buffer layer (here, x<y);
• forming a barrier layer made of AlzGa1-zN over the channel layer (here, x<z);
• forming a cap layer made of GaN over the barrier layer;
• forming a gate insulating film so as to be in contact with the cap layer;
• and
• forming a gate electrode over the gate insulating film.