Developing a methodology for the electron energy-loss spectroscopy of defects in GaN

The optical properties of wurtzite GaN are investigated using electron energy-loss spectroscopy (EELS). In this paper we develop a methodology to extract the information on the electronic structure from low-loss spectroscopy data and we apply this methodology to MgO as a test case. By considering the instrumental and methodological limitations of low-loss spectroscopy a decision whether it can be applied to a spatially resolved study of interband transitions and in particular differences in the band gap on and off crystal defects can be made. It is found that while the low-loss region provides the possibility of high-quality investigations of the optical properties of bulk materials, the limited spatial resolution due to delocalisation effects necessitates different tools for the study of nanometre scale defects, such as the near-edge fine structure of core excitations.