Using EELS to observe composition and electronic structure variations at dislocation cores in GaN

Since the earliest observations of dislocations, the majority of the experimental transmission electron microscope studies have focused on understanding their structural properties. However, the extensive use of heteroepitaxial growth for binary, ternary and even more complex semiconductor systems on lattice mismatched substrates has also highlighted the importance of dislocations in determining the overall electronic properties of devices. Electron energy loss spectroscopy, when used in conjunction with atomic resolution Z-contrast imaging, provides the ability to quantify changes in both composition and electronic structure (and, therefore, electronic properties) that occur at dislocations in these semiconductor systems. In this paper, the principles behind atomic scale electron energy loss spectroscopy are described and work on their application to threading dislocations in GaN thin films performed over the last 3 years is reviewed.