The effect of gate and recess scaling on the gate-drain breakdown and hot-electron reliability of AlGaAs/GaAs power HFETs

The gate-drain breakdown voltage (BV/sub DG/) ranks among the most significant figures of merit for microwave and millimeter-wave FETs, particularly high-power ones. Both an off-state and an on-state BV/sub DG/ can be defined and measured, the former being more or less a diode property, while the latter is linked with impact ionization in the device channel. To be sure, since the breakdown voltage is typically defined fixing a certain threshold value for the gate reverse current, the indication it provides is valuable, but assuming a direct relationship between BV/sub DG/ and the device reliability under high field conditions would be erroneous. This work speculates on the non-trivial correlation existing between the breakdown voltage and the device hot electron reliability and degradation, taking as a test vehicle power Al/sub 0.25/Ga/sub 0.75/As/GaAs HFETs with different gate lengths.