Impact of high-temperature operating lifetime tests on the stability of 0.15 μm AlGaN/GaN HEMTs: a temperature-dependent analysis

We present a detailed analysis of the effect of low- and high-temperature operating lifetime (LTOL and HTOL) carried out on 0.15 mu m GaN HEMTs for RF applications. Based on several stress experiments carried out at different temperature levels, a) we demonstrate the existence of two degradation modes consisting, respectively, in the negative and positive shift in the threshold voltage; b) temperature-dependent I-V measurements indicate that no modification in the Schottky barrier height takes place after stress; c) the negative VTH shift is ascribed to the temperature- and field-assisted de-trapping of electrons from the passivation/AlGaN stack under the gate, consistent with previous reports; d) the positive VTH shift, which only occurs at high temperature levels, is ascribed to the trapping of hot electrons, possibly at the AlGaN/SiN interface.