Microstructural evidence on direct contact of Au/Ge/Ni/Au ohmic metals to InGaAs channel in pseudomorphic high electron mobility transistor with undoped cap layer

Microstructural evidence on direct contact of Au/Ge/Ni/Au ohmic metals to a InGaAs channel in AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped GaAs/AlGaAs cap layer was found using transmission electron microscopy, and the results were used to interpret the electrical properties of the contact. The lowest contact resistivity of 3.8 X 10(-6) Omega cm(2), obtained at 420 degrees C annealing, is due to the penetration of the interfacial compounds, Au2Ga and Au2Al, into the buried InGaAs channel. The direct contact of the compounds to the channel causes the reduction of series resistances between the ohmic compounds and the channel, resulting in the low contact resistivity. (C) 1998 American Institute of Physics.