Determination of Bias-Dependent Source Resistances in GaAs MESFETs under Cold-FET Condition

A new method to determine bias-dependent source resistances for GaAs MESFETs is introduced. The method is a combination of the cold- and pinched-FET measurement techniques based on the real parts of the two-port impedances and their derivatives. The proposed method offers a unique extraction procedure only assuming that the channel doping profile is symmetric. The deleterious problems of negative source resistances in the pinched-FET condition and the deviation of α21 and α12 from 0.5 in the cold-FET condition are solved by deembedding the on-wafer pad parasitics. The usefulness of the method has been demonstrated by extracting source resistances for two types of MESFETs. The results were self-consistent enough to confirm the validity of this method.