Total-Ionizing-Dose Radiation Effects in AlGaN/GaN HEMTs and MOS-HEMTs

We have investigated the total ionizing dose (TID) radiation effects in AlGaN/GaN MOS-HEMTs as a function of dose and radiation bias, and compared them with conventional HEMTs. Under 10 keV X-ray irradiation, two distinct regimes of threshold voltage
$(V_{th})$
shifts have been revealed: a rapid
$V_{th}$
shift at low doses
$[< {3}{\rm krad (SiO}_{2})]$
for both HEMTs and MOS-HEMTs, and an additional
$V_{th}$
shift only found in MOS-HEMTs for doses up to at least 2 Mrad
$({\rm SiO}_{2})$
. The rapid
$V_{th}$
shift anneals quickly and is a strong function of layer material. We attribute this portion of the
$V_{th}$
shift to hole trapping in the AlGaN barrier layer. The
$V_{th}$
shift at high doses found only in MOS-HEMTs is attributed to hole trapping in the gate oxide. By comparing MOSFETs with
${\rm HfO}_{2}$
and
${\rm Al}_{2} {\rm O}_{3}$
gate dielectrics that are annealed during processing at various temperatures, we find that
$500^{\circ}{\rm C}$
annealed
${\rm HfO}_{2}$
shows the most promising TID response.