Sensitivity of on-resistance and threshold voltage to buffer-related deep level defectsin AlGaN/GaN high electron mobility transistors

摘要

The influence of deep levels defects located in highly resistive GaN:C buffers on the on-resistance (R_(ON)) and threshold voltage (V_(th)) of AlGaN/GaN high electron mobility transistors (HEMTs) power devices was studied by a combined photocapacitance deep level optical spectroscopy (C-DLOS) and photoconductance deep level optical spectroscopy (G-DLOS) methodology as a function of electrical stress. Two carbon-related deep levels at 1.8 and 2.85 eV below the conduction band energy minimum were identified from C-DLOS measurements under the gate electrode. It was found that buffer-related defects under the gate shifted V_(th) positively by approximately 10%, corresponding to a net areal density of occupied defects of 8 × 10~(12) cm~(-2). The effect of on-state drain stress and off-state gate stress on buffer deep level occupancy and R_(on) was also investigated via G-DLOS. It was found that the same carbon-related deep levels observed under the gate were also active in the access region. Off-state gate stress produced significantly more trapping and degradation of R_(on) (~140%) compared to on-state drain stress (~75%). Greater sensitivity of R_(on) to gate stress was explained by a more sharply peaked lateral distribution of occupied deep levels between the gate and drain compared to drain stress. The overall greater sensitivity of R_(ON) compared to V_(th) to buffer defects suggests that electron trapping is significantly greater in the access region compared to under the gate, likely due to the larger electric fields in the latter region.