Strukturelle Charakterisierung von Gruppe-III-Nitriden mit Hilfe der hochaufloesenden Roentgenbeugung

The investigation of typical defects in GaN layers is based on both X-ray results and transmission electron microscopy investigations from H. Selke. The defect structure in GaN layers grown on GaN nucleation layers is dominated by edge type threading dislocations and inversion domains. Furthermore, possible ion induced damages during molecular beam epitaxy were investigated, where acivated nitrogen for the GaN growth is delivered by a plasma discharge. By applying a substrate bias, nitrogen ions can be attracted or rejected during growth. Remarkable ion induced damages were found in GaN layers grown with an electron cyclotron resonance plasma source at negativ bias. The damages are comparable to those induced by ion implantation though the energies are much lower. The correlation of different kinds of defects with electrical and optical properties of the layers are presented in the last section of the work. It was found that not only the threading edge type dislocations can influence the Hall mobility and the full width at half maximum of the (D^0,X) emission but also the screw dislocations and stacking faults if the density of edge dislocations is approximately constant. Layers grown by molecular beam epitaxy on a GaN nucleation layer show an unknown emission around 3.440 eV.