SEARCHING FOR CORRELATIONS BETWEEN DISLOCATIONS AND TRAP STATES IN GALLIUM NITRIDE
Kevin Galiano, Drew Cardwell, Darryl Gleason, Pran Paul, Aaron Arehart, Steven Ringel, Jonathan Pelz.
The Ohio State University, Columbus, OH.
Gallium nitride, GaN, is a wide-bandgap semiconductor suitable for a variety of applications, including high temperature and high power electronics. Currently there is no good substrate for GaN. Often a substrate with a very different lattice constant is used for growth, and the different crystal structures between the substrate and the grown GaN film cause a large density of extended linear defects, known as dislocations. Electronic traps are defects where electrons can be captured, creating localized charge centers that alter device behavior. Electronic traps limit device performance and can lead to device degradation. It has been postulated that some traps are due to dislocation defects. Our goal is to characterize trap states and determine if they are localized at dislocations in GaN. Dislocations can alter the topography of GaN in characteristic ways depending on dislocation type and growth method. We have collected preliminary topography measurements using an atomic force microscope and have observed some features of individual dislocations. We are in the process of using an adaptation of scanning Kelvin-probe microscopy that we have developed, which we have named nano deep level transient spectroscopy, to look for trap states in GaN with nanometer-scale resolution. When a trap emits an electron, it causes a local charge transient, which is detected as a surface potential transient. An observation of specific traps located at dislocations would help us understand the origin of these traps in GaN and help lead to strategies to reduce their detrimental effects on device performance.