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

Abstract

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 1.2X10(-7) Ohm cm(2) at 300 degrees 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. (C) 1999 American Institute of Physics. [S0003-6951(99)03619-0].