In this letter, we have investigated hydrogen degradation of InP HEMT's wit
h Ti/Pt/Au gates. We have found that V-T shifts negative after exposure to
hydrogen, and exhibits an L-G and orientation dependence. We postulate that
Delta V-T is at least in part due to the piezoelectric effect, Hydrogen ex
posure leads to the formation of TiHx, producing compressive stress in the
gate. This stress induces a piezoelectric charge distribution in the semico
nductor that shifts the threshold voltage, We have independently confirmed
TiHx formation under our experimental conditions through Auger measurements
. Separate radius-of-curvature measurements have also independently confirm
ed that Ti/Pt films become compressively stressed relative to their initial
state after H-2 exposure.