Characterization of GaN MOSFETs on AlGaN/GaN Heterostructure With Variation in Channel Dimensions

GaN MOSFETs were developed on an AlGaN/GaN heterostructure in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure, and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. For devices with different types and sizes, discrepant field-effect mobilities were observed and the origins of the discrepancy were analyzed. One reason causing the discrepancy is the discrepancy of gate dimension between the design and fabrication. In devices with only mesa as the device isolation, the real channel width would be larger than the mesa width because a parallel channel might have formed in the isolation region just outside the device mesa. Boron ion implantation was found to be effective to cutoff the current path in the isolation region. Another reason causing the discrepancy is that the real channel length would be larger than the designed one owing to the lithography and gate dry recess process. To extract the correct mobility and effective channel length of the GaN MOSFET fabricated on AlGaN/GaN heterostructure with variation in the channel dimensions, several methods were proposed and compared basing on ring-type MOSFETs.