15.1 W/mm Power Density GaN-on-GaN HEMT With High-Gradient Stepped-C Doped Buffer

In this work, we propose for the first time a high-gradient (HG) stepped-Carbon (stepped-C) doped buffer design in GaN-on-GaN structures to enhance device RF performance. This design not only avoids the impact of the Fe tailing effect on the 2DEG but also effectively mitigates interface conduction losses caused by Si impurities at the regrown interface. Most importantly, the HG stepped-C buffer design significantly alleviates the trapping effects associated with high concentrations of C. The GaN-on-GaN HEMTs with HG stepped-C buffer achieved a breakdown voltage of 249 V, a peak transconductance ( ${g}_{\text {m}}\text {)}$ of 319 mS/mm with a low current collapse (CC) of 6.1%. Collectively, these factors enabled the GaN-on-GaN HEMTs to achieve ${f}_{\text {T}}$ / ${f}_{\max }$ values of 47.6 GHz/68.1GHz, with a state-of-the-art output power density ( ${P}_{\text {out}}\text {)}$ of 15.1 W/mm and a Power-Added efficiency (PAE) of 57.2% at 2 GHz. These results demonstrate the immense potential of HG stepped-C buffer in advancing the RF performance for GaN-on-GaN HEMTs.