Failure mode analysis of GaN-HEMT under high temperature operation

The purpose of this study is to investigate the physical mechanism of the threshold voltage shift of GaN-HEMT in high temperature storage tests. Using microscopic Raman spectrometry, we analyzed crystal distortion under the gate metal of devices which showed positive shift of the threshold voltage after heat treatments. Of heat treatment, the crystal extended vertically (c-axis direction). From this observation, we concluded that one possible reason for the threshold voltage shift in high temperature storage tests is the change of the piezoelectric polarization density dependent on the change of the crystal distortion under the gate metal.