Spatial Localization and Variation in Defect-Related Electron Traps in GaN Materials

High frequency transistors based on GaN have important applications in a variety of technologies, but can degrade due to defects of unknown origin. In particular, a class of defects with energy near 0.57 eV below the conduction band has been correlated with GaN device degradation [A. Arehart et al., Solid-State Electronics (2013)], has been observed for a wide variety of growth and processing conditions, and has been suggested to be clustered around physical defects [Z-Q Fang et al., J. Phys.: Condens. Matter (2002)]. We have used nm-scale Deep Level Transient Spectroscopy (nano-DLTS) [D. Cardwell et al., A.P.L. (2013)] on n-type GaN Schottky diodes grown by ammonia molecular beam epitaxy to confirm that these defects are indeed localized to “hotspots” with a density comparable to that of threading dislocations. Furthermore, our local nano-DLTS measurements reveal for the first time modest but distinct differences in trap energy and emission rate between hotspots, indicating that local conditions influence trap parameters even within a particular device. Ongoing work is directed towards determining the identity of the localized defects responsible for these detrimental traps, and what causes the trap parameters to vary with position.