MEASUREMENTS OF THE COMPONENTS OF SOURCE RESISTANCE OF HEMTS USING SLOTTED TRANSMISSION-LINE STRUCTURES

A new technique is presented which allows various components that cont ribute to the total parasitic source resistance in a conventional GaAs /AlGaAs HEMT to be measured. These components are the contact resistan ce to the n(+) GaAs cap, the sheet resistance of the unrecessed region between the ohmic contact pad and the gate recess, the barrier resist ance between the cap and the 2DEG sheet, and the sheet resistance of t he 2DEG layer. A standard transmission line arrangement with addition of slots of various widths in the n(+) cap between adjacent ohmic pads is used. Measurement of inter-pad resistances followed by a regressio n analysis allows various components to be separated. The data present ed shows the variation in barrier resistance with HEMT material layer structure e.g. Al mol fraction in the AlGaAs, space layer thickness, d oping concentration in the AlGaAs etc. The paper also shows that for m ost device applications, it is not necessary to make direct alloyed co ntact to the 2DEG sheet and that conduction via the n(+) cap is a more desirable contact mechanism. Copyright (C) 1996 Elsevier Science Ltd