The Influence of Fe Doping Tail in Unintentionally Doped GaN Layer on DC and RF Performance of AlGaN/GaN HEMTs

In this work, the performance of AlGaN/gallium nitride (GaN) high-electron mobility transistors (HEMTs) with different Fe doping tails was systematically investigated and compared. It is illustrated that the combination of the unintentionally doped (UID) GaN layer and a thinner Fe doping buffer layer would result in a faster slope rate of Fe concentration in the UID GaN layer. The devices with the fastest slope rate of Fe concentration in the UID GaN layer exhibited excellent large signal performance, including the saturated power density ( $P_{sat}$ ) of 9 W/mm and the power-added efficiency (PAE) of 65.6%. In addition, the $P_{sat}$ and the PAE of the device with the fastest slope rate of Fe concentration in UID GaN layer are 27.7% and 14.7%, which are higher than that of the device with the slowest slope rate of Fe concentration under the class AB operation conditions. Pulse I-V measurement results demonstrated that the buffer-related current collapse was more effectively suppressed in the 0.5-μm Fe doping buffer layer because of faster slope rate of Fe concentration in UID GaN layer. Moreover, the frequency-dependent capacitance and conductance measurement results indicated that the current collapse was relevant to deep traps in the UID GaN layer introduced by Fe doping. By reducing the concentration of the deep traps caused by Fe doping, the device showed excellent characteristics of dc and RF. Furthermore, controlling the Fe doping tail was important for designing the GaN-based power amplifier with high $P_{sat}$ and PAE.