Effects of surface micromesas on reverse leakage current in InGaN/GaN Schottky barriers

This work shows the correlation between excess reverse leakage currents in InGaN/GaN Schottky barrier diodes and the presence of surface micromesas on these structures. Surface micromesas with diameters of 1–2 μm and density in the range of 105 cm−2 were observed in metal-organic-chemical-vapor-deposition-grown InGaN (∼10 nm)/GaN epi-layers on c-sapphire substrates. Nomarski optical microscopy, scanning electron microscopy, and atomic force microscopy were used to investigate characteristics of the surface micromesas. We found that most of the surface micromesas originated from nanopipes in GaN as they intersected the InGaN/GaN epi-layer surface. Extensive current-voltage and Rutherford backscattering spectrometry measurements on the corresponding Ni-InGaN/GaN Schottky barriers revealed that these surface micromesas with nanopipes at their center were likely the main source of reverse leakage current. They also provide an easy metal diffusion path when devices undergo thermal annealing, even at relatively...