Self-aligned enhancement- and depletion-mode GaAs field-effect transistors employing the delta - doping technique during crystal growth by molecular-beam epitaxy.

This work describes a self-aligned Schottky-gate field-effect transistor (FET) which uses the delta - doping technique during crystal growth by molecular-beam epitaxy. In this new FET the delta - doping concepts are employed in three ways (i) for the highly doped surface to obtain non-alloyed 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 delta - doped electron-channel. The advantage of non-alloyed ohmic contacts allow us to use a new two-mask, self-aligned FET process to further reduce the parasitic resistances. Both, enhancement - and depletion-mode delta - doped GaAs field-effect transistor are fabricated. The measured tranconductance of the delta - doped field-effect transistor is 240mS/mm and is comparable to values obtained from selectively doped heterostructure transistors of the same geometry.