Hot electron effects on Al0.25Ga0.75As/GaAs power HFET's under off-state and on-state electrical stress conditions

This work shows a detailed comparison of the degradation modes caused by of f-state and on-state room temperature electrical stress on the de character istics of power AlGaAs/GaAs heterostructure field effect transistors (HFET' s) for X- and Ku-band applications, The devices are stressed under de bias conditions that result in electron heating and impact ionization in the gat e-drain region. Incremental stress experiments carried out at gate-drain re verse currents up to 3.3 mA/mm (for a total of more than 700h) show a remar kably larger degradation for the off- state stress, due to more pronounced electron heating at any fixed value of gate reverse current, This represent s an important piece of-information for the reliability engineer when it co mes to designing the accelerated stress experiments for hot electron robust ness evaluation. The degradation modes observed, all of a permanent nature, include threshold voltage and drain resistance increase and drain current and transconductance reduction.