Effect of Atmosphere on Electrical Characteristics of AlGaN/GaN HEMTs Under Hot-Electron Stress

Abstract

In this work, we demonstrate the degradation behavior and physical mechanism of AlGaN/GaN high-electron-mobility transistors (HEMTs) under hot-electron stress in hydrogen and nitrogen atmosphere. According to the monitoring results, the trends of ${I}_{\text {ds}}$ values are completely different during the same hot-electron stress in two types of atmosphere. The ${I}_{\text {ds}}$ values of the devices in pure hydrogen (the purity is 99.999%) continue decreasing at first and then remain at a fixed value, whereas the ${I}_{\text {ds}}$ values of the devices in pure nitrogen (the purity is 99.999%) recover to the initial value after the instability during the heating section and then instantaneously drop to zero 18 h after the beginning of the experiment. Comparing current–voltage ( ${I}$ – ${V}$ ) characteristics before and after the hot-electron stress experiment in hydrogen atmosphere, we find the output current decreases, the threshold voltage shifts forward, the gate leakage current increases, the current collapse enhances, and the gate-lag characteristic becomes worse. Based on our previous research, it can be concluded that hot-electron effects rather than hydrogen effects are the primary cause of device degradation. Moreover, the degradation in hydrogen atmosphere is more severe than that in nitrogen atmosphere according to the monitoring results of ${I}_{\text {ds}}$ values. We believe that the hydrogen can exacerbate the hot-electron effects through maintaining the lower junction temperature because of its higher thermal conductivity. A COMSOL finite-element simulation has been done to explain the mechanism.