Contact and Channel 3rd-Order Nonlinearity in III-N HFETs

A novel technique to reveal the contact and channel components of third-order nonlinearities in III-nitride heterostructure field-effect transistors (HFETs) is presented. We demonstrate close correspondence between the third-order intermodulation power (IM3) obtained from dc I-V's and directly from two-tone radio-frequency measurements. The transmission-line-method patterns have been used to extract separately the contact- and channel-related sources of nonlinearity. Relative contributions of mobility-field dependence and gate-bias-induced nonlinearities are compared. Contact and channel nonlinearity coefficients are found to have opposite signs, thus allowing for HFET design with contact and channel nonlinearities mutually compensating each other, which results in improved overall device linearity.