GEMOW REFRACTORY OHMIC CONTACT FOR GAAS/GAALAS SELF-ALIGNED HETEROJUNCTION BIPOLAR-TRANSISTORS

We have formed GeMoW and Ge(As)MoW ohmic contacts to n-type GaAs using different annealing techniques: rapid thermal annealing (RTA) or thermal furnace annealing under a forming gas, and sealed ampul or semi-open box technique under an As overpressure. A comprehensive study of both contacts is presented using electrical testing, Auger electron spectroscopy, secondary ion-mass spectrometry, and transmission electron microscopy. This study has led to the optimization of a new refractory ohmic contact, the As-doped Ge/Mo/W contact. Very low specific contact resistivities (10−7 Ω · cm2), have been obtained, when the contact included an As-doped Ge layer with a doping level of 1020 atm · cm−3 and was annealed using the semi-open box technique under an As overpressure. As doped GeMoW ohmic contacts have also been realized on GaAs/GaAlAs heterostructures, the specific contact resistivity is 4 × 10−7 Ω · cm2, which is a very low value for n-type refractory ohmic contact realized on GaAs/GaAlAs heterostructure. © 1990, The Electrochemical Society, Inc. All rights reserved.