Abstruct-A new degradation mechanism of PM-HEMT's subsequent to hot electron stress tests or high temperature storage tests is presented. A noticeable increase in drain-to-source current, IDS, is observed after the tests. We show that this IDS variation is slowly recoverable and is correlated with the presence of deep levels in the device. Stress tests cause a variation of trapped charge. Trapping of holes created by impact-ionization and/or thermally stimulated electron detrapping induce a variation of the net negative trapped charge, leading to a decrease in the threshold voltage, VT and a consequent increase in IDS. The correlation between %AVT and AIDS clearly demonstrates that the variation of trapped charge induced by hot electron tests is localized under the gate.

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New failure mechanisms induced by hot-electrons in AlGaAs/InGaAs pseudomorphic HEMTs have been identified by means of accelerated testing of commercial devices from four different suppliers. Different degradation modes have been observed, depending on the device type, namely: (a) recoverable increase of I/sub D/ and |V/sub T/|, which has been attributed to recombination of electrons trapped under the gate with holes generated by impact ionization; (b) enhancement of the kink in the output characteristics, possibly due to the generation of deep levels with subsequent electron trapping/detrapping; (c) permanent increase of the breakdown voltage, due to creation of negatively charged traps in the gate-drain region, yielding a wider space-charge region, hence a reduced maximum electric field. The link between the observed degradation modes and the underlying physical mechanisms is investigated by means of different techniques, and the main functional effects of the degradation modes are addressed

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