Hydrogen degradation of InPHEMTs and GaAsPHEMTs

We have carried out a systematic study of the impact of hydrogen exposure o n InP HEMTs and GaAs PHEMTs with Ti/Pt/Au gates. Hydrogen poisoning is an i mportant reliability concern in these devices. Our work has provided ample evidence supporting the formation of TiH inside the gate structure upon exp osure of HEMTs to a hydrogen environment. The resulting volume expansion of the gate stresses the semiconductor heterostructure underneath and, throug h the piezoelectric effect, results in a shift of the threshold voltage of the device. This mechanism is largely reversible. Independently of this, we have found that H-2 upsets the stoichiometry of the exposed InAlAs barrier in the recessed region right next to the gate. This irreversebly changes t he extrinsic sheet carrier concentration in the channel and affects other f igures of merit such as the breakdown voltage. This understanding should be instrumental in identifying device-level solutions to this problem.