Initial leakage current paths in the vertical type GaN on GaN Schottky barrier diodes
Electrical characteristics of leakage current paths in vertical type n GaN Schottky barrier diodes (SBDs) on free standing GaN substrates are investigated by using photon emission microscopy (PEM) The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current voltage characteristics.