DC Extraction of Gate Bias-Dependent Parasitic Resistances and Channel Mobility in an HEMT

In all high electron mobility transistors (HEMTs), the low field channel mobility, μ
₀
, is a function of gate bias. In GaN HEMTs, which have surface traps, the parasitic source/drain resistances, R
_S
/R
_D
, too are gate bias dependent, because electrons from the gate fill the traps nearby and deplete the 2-DEG over a length A on either side of the gate. We introduce a simple method to extract the gate bias dependence of μ
₀
, R
_S
, R
_D
, and the virtual gate length, Δ, from the measured dc resistance of gated and ungated devices fabricated on the same substrate.