Bulk and surface effects of hydrogen treatment on Al/Ti-gate AlGaAs/GaAs power HFETs

This work describes results of hydrogen degradation experiments performed on Al/Ti-gate AlGaAs/GaAs power HFETs. Upon storage at 180 degrees C for times up to a hundred hours in either 5% or 15% H-2/N-2 mixtures, the HFETs undergo significant changes of the electrical characteristics, due to mechanisms located either under the gate (bulk effects) or on the surface access regions on the gate sides (surface effects). The former lead to a threshold voltage reduction and thus to and increase of the drain current, attributed to the formation of TiH in the gate and the attendant piezoelectric charge in the underlying semiconductor; a degradation of the peak transconductance is also observed. As for the surface effects, we measure an increase of source-gate and drain-gate breakdown voltages, due to surface-state creation on the gate sides and to electron capture therein.