Abstract: The mechanism for increasing gate leakage current in recessed-gate AlGaN/GaN HEMTs,which are fabricated successfully by plasma dry etching,is investigated.Compared with conventional planar FETs,the gate leakage current of the recessed-gate AlGaN/GaN HEMTs increases by 10 times,and the breakdown voltage decreases to some extent.AFM and XPS are employed to measure the AlGaN surface before and after etching.The AlGaN surface becomes rougher,and even some protuberances like awl appear during dry etching.Thus the contact area between the metal and the semiconductor increases for the rougher AlGaN surface.On the other hand,some N vacancies generate plasma bombarding during dry etching.The N vacancies,which enhance the tunneling effect and reduce the Schottky barrier height,are regarded as n-type doped in the etched AlGaN surface.All these experiments indicate that the significant increase in the gate leakage current is due to the increased roughness and the appearance of these N vacancies in the AlGaN surface.

Key words: plasma dry etching, recessed-gate, gate leakage, N vacancies