Field effect transistor

A field effect transistor comprising:

• an active layer having a surface;
• a source electrode and a drain electrode disposed on the surface of the active layer;
• the active layer having, at the surface, a double-stage first gate recess between the source electrode and the drain electrode and a single-stage second gate recess between the first gate recess and the drain electrode, the double-stage first gate recess comprising a first-stage recess having an opening at the surface of the active layer and a second-stage recess having an opening at a bottom of the first-stage recess and a depth measured from the bottom of the first-stage recess, and the single-stage second gate recess having a depth equal to the depth of the second-stage recess;
• a first gate electrode disposed in the second-stage recess of the double-stage first gate recess and comprising a lower layer and an upper layer, the lower layer comprising a material having a resistivity and contacting the active layer, and the upper layer being disposed on the lower layer and comprising a material having a resistivity lower than the resistivity of the lower layer;
• and
• a second gate electrode disposed in the signal-stage second gate recess.

A field effect transistor comprising:

• an active layer having a surface and a first conductivity type;
• a source electrode and a drain electrode disposed on the surface of the active layer and spaced apart in a gate length direction;
• a gate electrode disposed on the surface of the active layer between the source electrode and the drain electrode and comprising a lower layer and an upper layer, the lower layer comprising a material having a resistivity and contacting the active layer, and the upper layer being disposed on the lower layer, comprising a material having a resistivity lower than the resistivity of the lower layer, and being longer than the lower layer in a direction parallel to the gate length direction;
• and
• an electrically conductive region in the active layer, reaching the surface of the active layer, spaced from, between, and electrically independent from the gate electrode and the drain electrode, the electrically conductive region having a second conductivity type opposite the first conductivity type, for controlling current flowing through the active layer.

A field effect transistor comprising:

• an active layer having a surface;
• a source electrode and a drain electrode disposed on the surface of the active layer and spaced apart in a gate length direction;
• a first gate electrode disposed on the surface of the active layer between the source electrode and the drain electrode;
• and
• a second gate electrode disposed on the surface of the active layer between the first gate electrode and the drain electrode, wherein the field effect transistor is divided into first and second halves by a center line parallel to the gate length direction, and,
• in the first half, the first gate electrode has a T-shaped cross-section and comprises a lower layer and an upper layer, the lower layer comprising a material having a resistivity and contacting the active layer, and the upper layer being disposed on the lower layer, comprising a material having a resistivity lower than the resistivity of the lower layer, and being longer than the lower layer in a direction parallel to the gate length direction, while the second gate electrode has a rectangular cross-section and a single layer, and,
• in the second half of the field effect transistor, the first gate electrode has a rectangular cross-section and a single layer while the second gate electrode has a T-shaped cross-section and comprises a lower layer and an upper layer, the lower layer comprising a material having a resistivity and contacting the active layer, and the upper layer being disposed on the lower layer, comprising a material having a resistivity lower than the resistivity of the lower layer, and being longer than the lower layer in a direction parallel to the gate length direction.