Investigation on the threshold voltage instability mechanism of p-GaN gate AlGaN/GaN HEMTs under high-temperature reverse bias stress

In this Letter, threshold voltage instability of p-GaN gate AlGaN/GaN HEMTs under high-temperature reverse bias (HTRB) stress has been investigated in detail. The experimental results show that the threshold voltage increases by 0.62 V after 100 ks stress at 200 degrees C. Especially, the degradation phenomenon is unrecoverable. A deep-level transient spectroscopy (DLTS) technique is used to characterize the defect evolution process during the stress. Two kinds of electron traps within the p-GaN layer were proposed to explain the degradation, which were generated by the injected high-energy electrons from the gate electrode. One is referred to as fixed charge trap, and another is trap E3 (E-C-0.7 eV). With the aid of high temperature, more electrons are injected and trapped in the fixed charge trap, which causes the permanent threshold voltage increase. In addition, the concentration and capture cross section of trap E3 were extracted as well, which are considered to dominate the recoverable degradation of the device due to the relatively shallower energy level.