Electron energy loss spectroscopy in the 2-5 eV regime

Localized electron energy loss Spectroscopy (EELS) studies in the bandgap energy regime were conducted in the GaN/3C-SiC and GaAlInP/GaAs materials systems. Requirements on experimental conditions and data analysis using the VG601UX and the possible interferences arising from instrumental factors and Cerenkov radiation losses are addressed. The bandgap of GaAs can be determined after subtraction of the zero loss peak. This procedure is, however, proned to introduce inaccuracies: GaAlInP shows deviations from the expected bandgap value of 0.5 eV. Materials not requiring subtraction of the zero loss peak fare better: the bandgap values of 3.3 and 3.1 eV obtained for GaN tie in with those obtained from Photoluminescence spectra for hexagonal and cubic GaN. Variations in the midgap states density vary with the location in the film and can be related to the amount of microstructural defects.