Influence of the substrate grade on structural and optical properties of GaN/AlGaN superlattices

The aspect of superior interfaces is studied using short-period GaN/AlGaN superlattices grown by Molecular Beam Epitaxy (MBE) on various substrates as versatile test structures for investigations of interface and layer properties. High-resolution x-ray diffraction pattern compared with simulations of ideal structures prove coherent 2-dimensional growth of structures with homogenous layer composition and atomically smooth and abrupt interfaces. The influence of structural perfection on optical properties is investigated in time-resolved photoluminescence measurements of selected superlattices. The recombination behavior of the excitons, their life time and the photoluminescence emission energy depend on the substrate quality and the superlattice structure. Furthermore it could be demonstrated that for optimal growth conditions the limiting factor for structural and optical properties of our MBE grown layers and heterostructures is the substrate.