TRAPPED CHARGE MODULATION - A NEW CAUSE OF INSTABILITY IN ALGAAS INGAAS PSEUDOMORPHIC HEMTS/

A new degradation mechanism of PM-HEMT's subsequent to hot electron st ress tests or high temperature storage tests is presented, A noticeabl e increase in drain-to-source current, I-DS, is observed after the tes ts, We show that this I-DS variation is slowly recoverable and is corr elated with the presence of deep levels in the device, Stress tests ca use a variation of trapped charge. Trapping of holes created by impact -ionization and/or thermally stimulated electron detrapping induce a v ariation of the net negative trapped charge, leading to a decrease in the threshold voltage, V-T and a consequent increase in I-DS. The corr elation between g(m) Delta V-T and Delta I-DS clearly demonstrates tha t the variation of trapped charge induced by hot electron tests is loc alized under the gate.