Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflächen

Optoelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1-100)- and especially the (-2110)-plane are quite corrugated. For the first time, the (-2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by x-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STM-measurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping.