Enhancement‐mode AlGaN/GaN HEMTs with thin and high Al composition barrier layers using O 2 plasma implantation

We report normally off AlGaN/GaN high‐electron mobility transistors realized by using the thin and high Al composition barrier design in conjunction with O 2 plasma implantation. The AlGaN barrier layer under the gate is selectively treated by low‐energy O 2 plasma in order to positively shift the threshold voltage of devices. The obtained enhancement‐mode HEMT exhibits a threshold voltage ( V TH ) of +1 V, a high peak transconductance of ∼230 mS mm −1 , and a maximum drain current of 424 mA mm −1 at a gate bias of 3 V for a gate length of 0.6 µm. A suppressed gate reverse leakage current and a high breakdown voltage of 450 V are achieved. Moreover, gradually partial oxidation of AlGaN barrier layer is determined to be responsible for the plasma‐induced V TH modulation effect through a systematic investigation. The results indicate O 2 plasma implantation can be a promising method for fabrication of enhancement‐mode GaN‐based devices.