A new Z11 impedance technique to extract mobility and sheet carrier concentration in HFET's and MESFET's

Conventional techniques to extract channel mobility, mu, and sheet carrier 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 impedance with the drain floating (Z(11)) over a broad frequency range, A transmission 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 technique 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 environment.