A study of DC and RF transconductance for different technologies of HEMT at low and high temperatures

We report on the measured effects of temperature on the DC and RF transconductance for several important HEMT technologies. Six different HEMT transistors were evaluated. Single- and double-heterojunction HEMTs, GaAs and GaN materials, virgin and multi-layer pHEMTs, and matched and pseudomorphic HEMTs are analyzed to enable a comparative and quantitative analysis for various transistor types. The temperature effects on the HEMT behavior vary remarkably with the considered transistor technology and working conditions. As a matter of fact, by changing the transistor and bias point, a higher temperature can yield an increase or decrease in the transconductance. It is worth noting that GaAs transistors have a bias point where the DC and RF transconductances are nearly invariant with temperature, owing to two opposing temperature effects canceling each other out, while no such bias condition was found for the GaN-based transistors.