Effects of traps formed by threading dislocations on off-state breakdown characteristics in GaN buffer layer in AlGaN/GaN heterostructure field-effect transistors

The off-state breakdown characteristics of GaN layers with different thicknesses from 0.2 to 2 mu m grown by metal organic chemical vapor deposition on SiC substrates were discussed using the space-charge-limited current conduction mechanism. With decreasing thickness of the GaN layer, the off-state breakdown voltage increased. The trap density in the GaN layer was estimated from the traps-filled-limit voltage, which determined the off-state breakdown voltage. We found that the thus-estimated trap density increased with decreasing thickness of the GaN layer. A higher density of threading dislocations in the thinner samples was confirmed by transmission electron microscopy observations. These results suggest that the traps formed by the threading dislocations influence the off-state breakdown voltage of the GaN layer. (c) 2008 The Japan Society of Applied Physics.