A NEW Z(11) IMPEDANCE TECHNIQUE TO EXTRACT MOBILITY AND SHEET CARRIERCONCENTRATION IN HFETS AND MESFETS

Conventional techniques to extract channel mobility, mu, and sheet car rier concentration, n(S), in heterostructure field-effect transistors (HFET's) do not account for the distributed nature of the device, This can result in substantial errors, To address this, we have developed a new technique that consists of measuring the gate-to-source impedanc e with the drain floating (Z(11)) over a broad frequency range, A tran smission line model (TL model) is fitted to Re[Z(11)], thus obtaining the gate capacitance and channel resistance (and consequently mu(V-GS) and n(S)(V-GS)) in a single measurement, We demonstrate this techniqu e in InAlAs/InGaAs on InP HFET's, The TL model faithfully represents Z (11) from 100 Hz to 15 MHz. Our technique can easily be automated and thus is a good tool for accurate charge control in an industrial envir onment.