On the fly characterization of charge trapping phenomena at GaN/dielectric and GaN/AlGaN/dielectric interfaces using impedance measurements

Charge trapping phenomena at interfaces of GaN-based semiconductors with a dielectric are one of the major concerns in modern MIS-HEMT technologies. Fundamental questions about the nature and the behavior of interface defects must still be answered. We address these questions by investigating devices with and without an AlGaN layer at the the interface with the dielectric, using MIS capacitor test structures. We consider different methodologies to perform and analyze impedance measurements and the results are compared and discussed. Special attention is paid to the uncertainties and limitations inherent to different techniques, as well as the challenges due to the composite structure of GaN/AlGaN devices. We introduce an on the fly technique which allows the extraction of the device drift during stress. This enables us to suggest a lower and upper boundary for the amount of device degradation. The experimental results indicate the presence of similar defects at GaN and AlGaN surfaces, which therefore appear to be intrinsic to the III-N material.