Hydrogen degradation in InP HEMTs

In this work we have investigated the degradation of InP HEMTs due to hydrogen exposure. We show for the first time that there are two independent degradation mechanisms that affect, respectively, the intrinsic and extrinsic portions of the device. Under the gate, H reacts with Ti and creates a TiH compound with a larger lattice that Ti. This induces stress and the resulting piezoelectric effect shifts the threshold voltage, V/sub T/, of the transistor. This mechanism is found to be largely reversible. In the recessed region next to the gate, hydrogen modifies the surface stoichiometry of the exposed InAlAs. This results in a reduction in the sheet carrier concentration underneath. This mechanism is not reversible.