A new Z/sub 11/ impedance technique to extract mobility and sheet carrier concentration in HFETs and MESFETs

Conventional techniques to extract channel mobility, /spl mu/, and sheet carrier concentration, n/sub s/, in heterostructure field-effect transistors (HFETs) 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/sub 11/) over a broad frequency range. A transmission line model (TL model) is fitted to Re[Z/sub 11/], thus obtaining the gate capacitance and channel resistance (and consequently /spl mu/(V/sub GS/) and n/sub s/(V/sub GS/)) in a single measurement. We demonstrate this technique in InAlAs-InGaAs on InP HFET's. The TL model faithfully represents Z/sub 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.