Hydrogen-induced piezoelectric effects in InPHEMT's

In this letter, we have investigated hydrogen degradation of InP HEMT's with 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 exposure leads to the formation of TiHx, producing compressive stress in the gate. This stress induces a piezoelectric charge distribution in the semiconductor 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 confirmed that Ti/Pt films become compressively stressed relative to their initial state after H-2 exposure.