Failure Mechanisms of AlGaAs/InGaAs Pseudomorphic HEMT's: Effects due to Hot-Electrons and Modulation of Trapped Charge

The reliability of AIGaAs/InGaAs pseudomorphic HEMT's has been investigated by means of thermal and hot-electron accelerated tests. Two commercially available devices have been tested, together with prototypes fabricated by a European supplier. Different failure modes have been observed after hot-electron testing, depending on the device type, i.e. (a) increase of drain current, Io and threshold voltage, I VTI, which can be attributed either to thermally-activated electron detrapping or to charge compensation by holes generated by impact ionization; (b) decrease of ID at low drain to source voltages, lids, with the development of a kink in the output characteristics, due to the generation of deep levels under the gate and subsequent electron trapping. In the former case, (a), hot carriers and/or high temperature storage only modulate the charge present on deep levels, leading to recoverable alterations of device characteristics. In the latter case, (b), the presence of additional deep levels under the gate leads to a permanent degradation. The link between the observed failure modes and the underlying physical mechanism is investigated by means of different techniques, and the main functional effects of the degradation modes are addressed.