The electrical characteristic and trapping effect of AlGaN/GaN HEMTs with Fe and Fe/C co-doped GaN buffer layer

In this work, the influence of the Fe and Fe/C co-doped buffer on the AlGaN/GaN HEMTs is systematically investigated and compared. Due to the pronounced Fe tail in the unintentionally doped layer of the Fe-doped buffer compared to the Fe/C co-doped buffer, and the utilization of a two-step C doping process in the Fe/C co-doped buffer, it results in effectively reducing leakage current and increasing breakdown voltage without sacrificing saturation current and peak transconductance. Meanwhile, the RF characteristics of the Fe/C co-doped buffer are also superior to the Fe-doped buffer. More importantly, Drain Transient Current measurements indicate that the current collapse in the Fe/C co-doped buffer is smaller than that in the Fe-doped buffer. Through simulation analysis, the reason was identified: In the near-channel region, the weaker Fe tail effect in Fe/C co-doped buffer leads to a lower acceptor trap ionization. When the concentration of C exceeds 1 × 1016 cm−3, the ionization of traps introduced by Fe is suppressed. Additionally, the two-step C impurity distribution in the Fe/C co-doped buffer design modulates the electric field and potential, reducing the effective range of the electric field and potential, thereby effectively reducing the trap effects. These results are highly meaningful for the design of high-power amplifier epitaxial structures.