Study on the Correlation between Etch Pit Morphologies and Dislocation Structures in GaN Films by Transmission Electron Microscopy

Abstract

Gallium nitride (GaN) is a core semiconductor used in everything from power devices to LEDs. However, the high density of structural defects present within thin films remains a key factor degrading device reliability and performance. Therefore, identifying and controlling these defects is a major challenge for both the research community and industry. In this study, defect-selective wet chemical etching was employed to evaluate the location and density of defects within ultrathin GaN films. Subsequently, the types and atomic arrangements of dislocations within the wurtzite structure were observed. GaN specimens were fabricated using molecular beam epitaxy (MBE) by growing a 10 nm thick AlN epitaxial buffer layer on a Si substrate followed by a 100 nm thick GaN layer. Subsequently, KOH-NaOH molten solution etching was employed to non-destructively visualize the defect distribution within the ultrathin film. We utilized weak-beam dark-field (WBDF) transmission electron microscopy (TEM) to distinguish edge, screw, and mixed threading dislocations, clearly defining their relationship with etch pits on the dislocation surfaces. Unlike past research focused on bulk GaN, this study concentrated on ultra-thin GaN layers. It highlighted the unique defect behavior in a 100 nm GaN layer and revealed the atomic-scale mechanisms governing the formation and evolution of etch pit-dislocation interactions.