Transistor and method of fabrication of the same including a gate contact formed in a recess through the passivation dielectric layer in contact with the active layer

A method for producing a transistor structure, comprising the following steps:

• a) providing a substrate (110, 210) with a piezoelectric active layer (112, 212) having a heterojunction disposed on the substrate (110, 210);
• b) applying a dielectric passivation layer (120, 220) with a first stress value onto the active layer (112, 212), wherein the passivation layer (120, 220) has a thickness of between 10 nm and 1000 nm;
• c) producing a recess (122, 222) in the passivation layer (120, 220), wherein the recess (122, 222) extends through the entire passivation layer (120, 220) in the direction of the active layer (112, 212) and on the boundary to the active layer (112, 212) has a width of between 10 nm and 500 nm, wherein the ratio between the thickness of the passivation layer (120, 220) and the width of the recess (122, 222) on the boundary to the active layer (112, 212) is between 1.5:1 and 4:1;
• d) developing a gate contact element (140, 240) disposed within the recess (122, 222), wherein the contact element (140, 240) extends from the active layer (112, 212) to above the passivation layer (120, 220);
• e) applying of a cover layer (150, 250) with a second stress value, which covers over the contact element (140, 240) above the passivation layer (120, 220);
• characterized in that
• f) the development of at least one layer (120, 220, 150, 250) disposed above the active layer (112, 212) is conducted in a tensile stressed or compressively stressed manner in the area around the contact element (140, 240) with a normal tension of |σ|>1 GPa, or the development of the cover layer is conducted in a tensile stressed manner with a normal tension of σ>200 MPa, wherein via the individual stresses in the area around the contact element (140, 240), a resulting force on the boundary area between the passivation layer (120, 220) and the active layer (112, 212) is set, which influences via the piezoelectric effect the electron density in the active layer (112, 212) in the area below the contact element (140, 240), wherein the normal tensions of stressed layers lie in the range between ±4 GPa.