An atomic-level controlled etching (ACE) technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with high power added efficiency.We compare the recessed gate HEMTs with conventional etching (CE) based chlorine,Cl2-only ACE and BCl3/Cl2 ACE,respectively.The mixed radicals of BCl3/Cl2 were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl3/Cl2 ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency (PAE) of 59.8％ with an output power density of 1.6 W/mm at Vd =10 V,and a peak PAE of 44.8％ with an output power density of 3.2 W/mm at Vd =20 V in a continuous-wave mode.