PD GE/TI/AU OHMIC CONTACT TO ALGAAS/INGAAS PSEUDOMORPHIC HIGH-ELECTRON-MOBILITY TRANSISTOR WITH AN UNDOPED CAP LAYER/

The Pd/Ge/Ti/Au ohmic contact to AlGaAs/InGaAs pseudomorphic high elec tron mobility transistor was investigated with the etch depth of an un doped GaAs/AlGaAs cap layer. The contact resistivity decreases from 9. 5 x 10(-5) to 2.3 x 10(-6) Omega cm(2) when the contacts were formed o n a n-Al0.23Ga0.77As layer by removing the undoped cap layer. X-ray di ffraction results show that the good ohmic contact is due to the forma tion of Au2Al as well as beta-AuGa. Both compounds play a role to crea te group-III vacancies, followed by the incorporation of Ge into group -III vacancies, namely, creation of free electron below the contact. T his results in the considerable elimination of contact resistivity by lowering the effective tunneling barrier. (C) 1997 American Institute of Physics.