Self-aligned enhancement-mode and depletion-mode GaAs field-effect transistors employing the δ-doping technique

This work describes a self-aligned Schottky-gate field-effect transistor (FET) which uses the δ-doping technique during crystal growth by molecular beam epitaxy. In this new FET the δ-doping concepts are employed in three ways: (i) for the highly doped surface to obtain nonalloyed ohmic contacts, (ii) to decrease the parasitic resistances, and (iii) for the electron channel below the gate. A two-dimensional electron gas in a V-shaped quantum well is formed by the δ-doped electron channel. The advantage of nonalloyed ohmic contacts allows us to use a new two-mask, self-aligned FET process to further reduce the parasitic resistances. Both enhancement-mode and depletion-mode δ-doped GaAs field-effect transistors are fabricated. The measured transconductance of the δ-doped field-effect transistor is 240 mS/mm and is comparable to values obtained from selectively doped heterostructure transistors of the same geometry.