HIGH-ELECTRIC-FIELD TRANSPORT EFFECTS ON LOW-TEMPERATURE OPERATION OF PSEUDOMORPHIC HEMTS

High electric field effect in very small pseudomorphic High Electron Mobility Transistor (HEMT) Al0.22Ga0.78As/In0.2Ga0.8As/GaAs and their influence at low temperature are investigated for 0.1mum up to 0.4mum gate lengths. The extent of transport improvement at low temperature and performance degradation associated with gate length reduction are underlined. Limitations in performance improvement appear at low temperature due to trapping effects and to an enhancement of the mechanisms responsible of short channel effects. In pulsed drain operation the evolutions of drain current versus time in the 10ns-600mus range illustrate the influence of trapping centers and self heating of the lattice in the device. We analyze the variation of gate current versus temperature at high drain bias (>3V) and the influence of impact ionization.