Discrepancies obtained in transconductance extracted from pulsed I-V curves and from pulsed S-parameters in HEMTs and PHEMTs

An isothermal comparison between the transconductance extracted from S-parameter measurements (gm_RF) and the transconductance derived from I-V curves (gm_IV) is performed for HEMT and PHEMT transistors. The isothermal environment is achieved by carrying out a complete pulse characterisation (pulsed I-V and pulsed S-parameters) that avoids the effects of self-heating. Results show a gm_RF that can be > 40% larger than gm_IV at high V-gs voltages. Thermal effects are avoided during the pulsed characterisation, therefore this discrepancy is attributed to fast traps.