Temperature and bias investigation of self heating effect and threshold voltage shift in pHEMT's

The output I−V characteristics of our devices are also affected by the threshold voltage shift. It results that the threshold voltage increases linearly by decreasing the temperature. This threshold voltage shift causes a decrease of the transconductance when the devices is biased closer to the pinch-off. Consequently, the forward transmission parameter S21 at microwaves shows a degradation at lower temperatures despite the fact that the transport properties improve upon cooling.