TEM Observation of Crack- and Pit-Shaped Defects in Electrically Degraded GaN HEMTs

Abstract

AlGaN/GaN high-electron mobility transistors stressed under dc bias at various channel temperatures were studied using transmission electron microscopy for evidence of physical damage. Stressed devices consistently developed crack- and pit-shaped defects in the AlGaN/GaN crystal material under the drain-side edge of the gate, whereas side-by-side as-processed unstressed devices did not show these features. Furthermore, the amount of physical damage was found to correlate to the amount of electrical degradation as measured by the change in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ID</i> max from before and after stress. The formation of these defects is consistent with the theory of damage from the inverse piezoelectric effect.