FAILURE MECHANISMS OF ALGAAS INGAAS PSEUDOMORPHIC HEMTS - EFFECTS DUETO HOT-ELECTRONS AND MODULATION OF TRAPPED CHARGE/

The reliability of AlGaAs/InGaAs pseudomorphic HEMT's has been investi gated by means of thermal and hot-electron accelerated tests. Two comm ercially available devices have been tested, together with prototypes fabricated by a European supplier. Different failure modes have been o bserved after hot-electron testing, depending on the device type, i.e. (a) increase of drain current, I-D and threshold voltage, \V-T\ which can be attributed either to thermally-activated electron detrapping o r to charge compensation by holes generated by impact ionization; (b) decrease of I-D at low drain to source voltages, V-DS, with the develo pment of a kink in the output characteristics, due to the generation o f deep levels under the gate and subsequent electron trapping. In the former case, (a), hot carriers and/or high temperature storage only mo dulate the charge present on deep levels, leading to recoverable alter ations of device characteristics. In the latter case, (b), the presenc e of additional deep levels under the gate leads to a permanent degrad ation. The link between the observed failure modes and the underlying physical mechanism is investigated by means of different techniques, a nd the main functional effects of the degradation modes are addressed. (C) 1997 Elsevier Science Ltd.