  Short-term reliability and robustness of 110 nm AlN/GaN HEMTs has been
evaluated by means of off-state, semi-on state and on-state step stress tests
on devices having different gate-drain distance, LGD. While breakdown voltages
and critical voltages scale almost linearly with LGD, failure mode remains
almost unchanged in all tested devices, and consists in an increase of gate
leakage, accompanied by a positive shift of threshold voltage. In off-state,
electroluminescence images detect the presence of localized leakage paths which
may act as preferential paths for electron trapping. Degradation does not
depend on dissipated power and is preliminary attributed to hot-electron
trapping, enhanced by electric fields.
