CONTACT RESISTANCE MEASUREMENTS IN GAAS-MESFETS AND MODFETS BY THE MAGNETO-TLM TECHNIQUE

The standard transmission-line model (TLM) for specific contact resistivity measurements of planar contacts is improved in two ways: (i) the addition of a magnetic field, which gives the mobility and carrier concentration of the bulk material, and the mobility of the material under the contact; and (ii) an extension of two layers, which makes the model applicable to MODFET structures. The results are applied to GaAs MESFET material, and AlGaAs/InGaAs MODFET material. One conclusion concerning the latter material is that the InGaAs electrons directly beneath the annealed Au/Ge/Ni contacts have lower mobility than those in the bulk, but still maintain 2DEG character.