Abstract: A passivation method is developed, and the effects and mechanism of this passivation method on the performance of AlGaN/GaN HEMTs and are investigated.The key aspect of this passivation technique is that AlGaN/GaN HEMTs are pretreated with a mix of hydrochloric acid and hydrofluoric acid (HF∶HCl∶H2O=1∶4∶20) prior to Si3N4 deposition.Compared with devices passivated only with Si3N4 deposition, the devices fabricated with the mixing solution treatment prior to Si3N4 passivation show minimal gate reverse leakage and little current collapse effect induced by DC bias stress.The density of the output power increases to 5.2W/mm, exhibiting good electrical reliability.X-ray photoelectron spectroscopy is employed to measure the AlGaN surface before and after pretreatment.The decrease of the oxygen ratio in the AlGaN surface after surface treatment reduces the concentration of surface states and surface charge traps, which is regarded as the major reason for the performance improvement of AlGaN/GaN HEMTs

Key words: AlGaN/GaN HEMTs, passivation, surface pretreatment, native oxide