Investigation of defect states in AlGaN/GaN high electron mobility transistors by small-signal admittance analysis

We have performed a small-signal admittance analysis to extract trap parameters in an AlGaN/GaN high electron mobility transistor-on-Si. Whereas the admittance in the accumulation- and depletion-bias regimes is primarily due to the interface traps, the admittance near the threshold voltage and below is due to mono-energetic traps inside GaN. The density extracted for threading dislocation-related 1D traps at ≈ 0.22 eV below the GaN conduction band edge is similar to that previously reported by reverse-biased gate leakage analysis of the analyzed device. Our analysis suggests additional 1D traps of comparatively lower density ≈ 4 × 10 14 cm − 3 but considerably large capture cross section ≈ 8 × 10 − 14 cm 2 in the GaN layer at ≈ 0.31 eV below the conduction band. The AlGaN trap density is considerably larger near the AlGaN/GaN interface than in the bulk AlGaN. The AlGaN traps mainly contribute to the voltage stretch; their admittance contribution is negligible. Gate leakage dominates the conductance at lower frequencies.