Performance enhancement by using the n⁺-GaN cap layer and gate recess technology on the AlGaN/GaN HEMTs fabrication

Due to the low mobility and wide bandgap characteristics of the undoped AlGaN layer used in the conventional AlGaN/GaN HEMT as a cap layer, the dc and rf performances of the device will be limited by its disadvantages of high ohmic contact resistance and high knee voltage. In this study, we proposed by using the n⁺-GaN cap layer and the selective gate recess etching technology for the AlGaN/GaN HEMTs fabrication. With this n⁺-GaN instead of the undoped AlGaN as a cap layer, the device contact resistance can be reduced from 1.0 Ω-mm to 0.4 Ω-mm. The recessed device demonstrated an I _ds,max of 1.03 A/mm, a g_m, max of 220 mS/mm, an f _T of 26 GHz, an f_max of 50 GHz, and an output power density of 2.6 W/mm at 2.4 GHz.