Many ternary and quaternary semiconductor compounds are characterized by a large thermodynamic miscibility gap affecting the phase stability and showing phase separation tendencies with composition fluctuations on the nanometer scale. The incorporation of Indium in ternary (In,Ga)N alloys differs from two-dimensional planar films to three-dimensional nanowires because of the complex interplay between phase instabilities, surface and interface roughening and epitaxial strain relaxation processes. Here, Indium concentrations up to 50% are feasible in (In,Ga)N/GaN nanowires. A strong lattice pulling effect at the (In,Ga)N/GaN interface is determined by spatially-resolved electron energy-loss spectroscopy in combination with a specific strain relaxation mode interacting between elastic and plastic relaxation processes. In a next step, Synchrotron x-ray diffraction measurements are planned at BESSY II to monitor the lattice pulling effect in-situ during growth (in collaboration with Core Research Area Nanofabrication).
Clustering in epitaxial Gadolinium doped GaN thin films has been identified as resulting of phase separation and strain minimization processes and is discussed in the frame of density functional theory. Even in the case of low Gadolinium concentrations, local lattice distortions are detectable, which are caused by coherent bi-layer GdN platelets with about 2 nm lateral size, which are formed during growth along the GaN basal planes.