A new Z11 impedance technique to extract mobility and sheet carrier concentration in HFETs and MESFETs

Conventional techniques to extract channel mobility, μ, and sheet carrier concentration, n_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 (Z₁₁) over a broad frequency range. A transmission line model (TL model) is fitted to Re[Z₁₁], thus obtaining the gate capacitance and channel resistance (and consequently μ(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 Z₁₁ 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