Effects of Applied Bias and High Field Stress on the Radiation Response of GaN/AlGaN HEMTs

The sensitivity of GaN/AlGaN HEMTs to 1.8 MeV proton irradiation is greatly enhanced by biasing the devices during irradiation and/or applying high field stress before irradiation. The resulting defect energy distributions are evaluated after irradiation and/or high field stress via low-frequency noise measurements. Significant increases are observed in acceptor densities for defects with
$\sim $
0.2 and
$\sim $
0.7 eV energy levels. These defects appear to dominate the degradation in threshold voltage and transconductance for these devices. Density functional theory (DFT) calculations show that N vacancy-related defects in GaN and hydrogenated O
${_{\rm N}}$
complexes in AlGaN are strong candidates for the defects with
$\sim $
0.2 eV energy levels in these devices. We also present evidence that the previously unidentified
${\sim} $
0.7 eV defect in GaN is a N anti-site defect (N
$_{\rm Ga}$
).