Temperature dependence of high-frequency performance of AlGaAs/InGaAs pseudomorphic HEMT's

High-frequency measurements of 1.5- mu m gatelength AlGaAs/InGaAs pseudomorphic HEMTs have been performed at temperatures ranging from 77 to 463 K. A 28% increase and 27% decrease in f/sub T/ were observed by changing the temperature from 300 to 77 K and from 300 to 463 K, respectively. The effective saturation velocity evaluated from the total delay time, 1/2 pi f/sub T/, versus reciprocal I/sub DS/ relation reveals almost the same temperature dependence as f/sub T/. It is also shown that the temperature dependence is similar to that of calculated velocity at high electric fields but not to that at low fields. This suggests that the temperature dependence of the HEMT performance is determined by that of the saturation velocity in the channel.>