Time-Resolved Micro-Beam X-Ray Absorption Fine Structure (XAFS) Measurement to Investigate the Cause of a Current Collapse of GaN-HEMTs

The purpose of our work was to carry out a direct measurement of a GaN's surface condition under a voltage stress, and to identify a cause of a current collapse. Using pulsed S-parameters measurements immediately after the voltage stress was applied for the GaN HEMT, equivalent circuit parameters were extracted, and we estimated the virtual gate length which induced the current collapse. And we carried out time resolved micro-beam X-ray Absorption Fine Structure (XAFS) measurement after the voltage stress was applied. As a result, by the applied voltage stress, an X-ray Absorption Near Edge Structure (XANES) spectrum of gallium, Ga, was found to be changed. This means the surface condition of GaN was changed in the virtual gate region by the voltage stress.