Application of nonalloyed PdGe ohmic contact to self-aligned gate AIGaAs/InGaAs pseudomorphic high-electron-mobility transistor

A self-aligned gate pseudomorphic high-electron-mobility transistor (PHEMT) was developed through nonalloyed PdGe ohmic contact on an n⁺-GaAs cap layer. The lowest contact resistivity obtained was 1.2×10^-7 Ω cm² at 300°C. This allows us to change the sequence on the formation of source/drain and gate electrodes in the process of PHEMT fabrication, namely self-aligned gate PHEMT. Performance of the self-aligned gate PHEMT was remarkably pronounced with annealing temperature or the decrease of contact resistivity. This is due to the solid-phase regrowth of highly Ge-doped GaAs below the PdGe contact, which acts to reduce barrier height for electron tunneling.