Detailed Study of Zero Temperature Coefficients for Microwave GaAs and GaN FETs

Detailed study of zero temperature coefficients (ZTC) for microwave GaAs and GaN based high electron mobility transistors were reported and analysed. The measured temperature-dependent data between -40 to 150°C were observed of transconductance and drain current for the both devices. It was found that the variation of threshold voltage (V T) with the drain bias (V ds) has an influence on zero temperature coefficient points. Furthermore, the drain current based ZTC point arises before VT for GaN and after VT for GaAs FETs with respect to drain bias. Inconsistency are observed; most conspicuously that the temperature trends of the threshold voltage for these two device technologies are utterly contrasting. In addition, transconductance based ZTC is absent in GaN device. Furthermore, the effective mobility is estimated using an improved model for the GaN device. The results indicate a well-confined 2-DEG with high mobility as the peak value of effective mobility closely corresponds with the Hall mobility. This work provides some worthwhile insights in microwave circuits design for high temperature applications.