Semiconductors are the backbone of modern day electronics. They are defined by their ability to either block or conduct the flow of electrons. At interfaces and in nanostructures, the electronic properties of solids can differ substantially from bulk material. They are sensitive to strain and distortions in the crystal structure. We use this to intentionally modify the electronic structure at the interfaces of materials with different structural parameters. The result is systems with extraordinary electronic and optical functionality.
For designing materials on the nano-scale, a profound understanding and control of material growth mechanisms is the basis. PDI is internationally recognized for its high expertise in the fabrication of atomically well-defined semiconductor structures. We focus on compound semiconductor materials combining group III (Ga, In, Al) and V (As, N) elements, but have lately been expanding our material selection to oxides, tellurides and more exotic material such as graphene. These structures are fabricated using molecular-beam-epitaxy (MBE), a technique that allows highest control of the growth process and is especially well suited for the study of novel material. Using this technique, we can combine materials with largely different structural properties, which would not be stable under normal conditions. This is what we call “extreme hetero-epitaxy” – a core strength of the institute. For research purposes, we are mostly interested in structures that limited in at least one direction to only a few atomic layers. Modern microscopic techniques allow the visualization of their crystal structure down to a resolution of single atoms. A wide selection of optical spectroscopic experiments yields further information on the structure, for example its electronic and optical properties. Hand-in-hand with the experiments, computational modeling is used to predict and interpret the results.