Group III nitride semiconductor device

A semiconductor device comprising:

• a first layer comprising a group III nitride semiconductor of a first conductivity type,
• a second layer comprising a group III nitride semiconductor of a second conductivity type,
• a third layer comprising a group III nitride semiconductor of the first conductivity type, and
• a gate electrode,
• wherein the first layer is provided between the gate electrode and
• the third layer;
• wherein the third layer is provided between the first layer and the second layer;
• wherein the band gap of the third layer is less than the band gap of the first layer;
• and
• wherein the first layer and the third layer have the thickness dimension so that a depleted layer developed from the second layer when no electric voltage is applied to the gate electrode expands up to a surface of the first layer at a side where the gate electrode is located.

A semiconductor device comprising:

• a first layer comprising a group III nitride semiconductor of a first conductivity type,
• a second layer comprising a group III nitride semiconductor of a second conductivity type,
• a third layer comprising a group III nitride semiconductor, and
• a gate electrode,
• wherein the first layer is provided between the gate electrode and the third layer;
• wherein the third layer is provided between the first layer and the second layer;
• wherein the band gap of the third layer is less than the band gap of the first layer and the second layer, and
• wherein the first layer and the third layer have the thickness dimension so that a depleted layer developed from the second layer when no electric voltage is applied to the gate electrode expands up to a surface of the first layer at a side where the gate electrode is located.

A field-effect transistor comprising:

• a gate electrode;
• a first layer comprising a group III nitride semiconductor of a first conductivity type;
• a second layer comprising a group III nitride semiconductor of a second conductivity type located on a side of the first layer opposite to the gate electrode,
• a third layer located between the first layer and the second layer;
• and
• an electrode being in contact with the first layer and the second layer,
• wherein the third layer has a band gap smaller than the band gaps of the first layer and the second layer.

A field-effect transistor comprising:

• a gate electrode;
• a first layer comprising a group III nitride semiconductor of a first conductivity type;
• a second layer comprising a group III nitride semiconductor of a second conductivity type located on a side of the first layer opposite to the gate electrode,
• a third layer located between the first layer and the second layer;
• and
• an electrode being in contact with the first layer and the second layer,
• wherein the third layer comprises a group III nitride semiconductor of the first conductivity type and has a band gap smaller than the band gap of the first layer.

A field-effect transistor comprising:

• a gate electrode;
• a first layer comprising a group III nitride semiconductor of a first conductivity type;
• and
• a second layer comprising a group III nitride semiconductor of a second conductivity type located on a side of the first layer opposite to the gate electrode,
• wherein the first layer has a thickness dimension so that a depleted layer developed from the second layer when no electric voltage is applied to the gate electrode expands up to a surface of the first layer at a side where the gate electrode is located.