Effects of DC and AC stress on the VT shift of AlGaN/GaN MIS-HEMTs

AlGaN/GaN MIS-HEMTs with adjusted VT were fabricated using a recess gate to investigate the effect on actual operation when the polarity of the gate voltage is opposite in the on- and off-state. The direction and time exponents of VT shift depend on the polarity of the gate bias stress. Electrons detrapping from the Al2O3/AlGaN interface trap site to AlGaN under negative gate bias stress has to overcome the energy barrier, resulting in a higher temperature dependence. In addition, the unaffected gm and SS show that the degradation occurred primarily at the Al2O3/AlGaN interface rather than channel or mobility degradation. For unipolar and bipolar AC stresses, the time exponent of the VT shift during stress time has two values, and a relatively low value during relaxation after bipolar AC stress. These results may be due to the further degradation by Vmin at the broader energy levels of the Al2O3/AlGaN interface.