HIGH-ELECTRIC-FIELD TRANSPORT EFFECTS ON LOW-TEMPERATURE OPERATION OFPSEUDOMORPHIC HEMTS

High electric field effect in very small pseudomorphic High Electron M obility Transistor (HEMT) Al0.22Ga0.78As/In0.2Ga0.8As/GaAs and their i nfluence at low temperature are investigated for 0.1mum up to 0.4mum g ate lengths. The extent of transport improvement at low temperature an d performance degradation associated with gate length reduction are un derlined. Limitations in performance improvement appear at low tempera ture due to trapping effects and to an enhancement of the mechanisms r esponsible of short channel effects. In pulsed drain operation the evo lutions of drain current versus time in the 10ns-600mus range illustra te the influence of trapping centers and self heating of the lattice i n the device. We analyze the variation of gate current versus temperat ure at high drain bias (>3V) and the influence of impact ionization.