A Model for Hydrogen-Induced Piezoelectric Effect in InP HEMTs and GaAs PHEMTs

We have developed a model for the impact of the hydrogen-induced piezoelectric effect on the threshold voltage of InP HEMTs and GaAs PHEMTs. We have used two-dimensional (2-D) finite element simulations to calculate the mechanical stress caused by a Ti-containing metal gate that has expanded due to hydrogen absorption. This has allowed us to map the 2-D piezoelectric charge distribution in the semiconductor heterostructure. We then used a simple electrostatics model to calculate the impact of this piezoelectric polarization charge on the threshold voltage. The model explains experimental observations of hydrogen-induced threshold voltage shifts, both in InP HEMTS and in GaAs PHEMTs. It also suggests ways to mitigate the hydrogen sensitivity of these devices.