Failure mechanisms of Schottky gate contact degradation and deep traps creation in AlGaAs/InGaAs PM-HEMTs submitted to accelerated life tests

In this work we analyze degradation phenomena observed in pseudomorphic AlGaAs/lnGaAs HEMTs with Al/Ti gate metallization, which have been submitted to accelerated tests at high drain-source voltage V-DS and high power dissipation P-D. After these tests, we observe permanent degradation effects, consisting in electron trapping in the gate-drain access region, with consequent decrease in the longitudinal electric field and "breakdown walkout", and in thermally-activated interdiffusion of the Al/Ti gate with decrease in the gate Schottky barrier height and increase in drain saturation current I-D. Rather than causing a degradation of therf characteristics of the device, these phenomena induce an increase in the associatedrf gain at 12 GHz, the other rf characteristics being almost unchanged. Overall, the most relevant failure mode observed is an increase of low-frequency transconductance. (C) 1998 Elsevier Science Ltd. All rights reserved.