Research

One basic requirement for semiconductor biosensors based on hybrid organic-inorganic structures is the covalent attachment of functional organic layers to the semiconductor surface – the so-called functionalization. Due to the different polytypes and its excellent biocompatibility, Silicon Carbide (SiC) in this context is a very promising semiconductor with a wide bandgap, composed in equal parts of silicon and carbon.

One way to attach organic alkyl monolayers to semiconductors without an intermediate oxide layer is based on hydrogen-termination of the semiconductor surface. In the case of silicon, the formation of Si-H bonds on the surface can be achieved using hydrofluoric acid. The functionalization process, which selectively attaches alkene molecules to the surface Si-H bonds, is known as hydrosilylation. This is a chain reaction process, where the surface-bound hydrogen is homolytically cleaved and the organic molecule binds to the silicon surface via an Si-C bond. Our work is focused on the extension of this process to Silicon Carbide, which in contrast to silicon offers the opportunity to exploit the crystal polarity and the variation of the energy position of the conduction band edge amongst the various SiC polytypes to tailor the interaction between the semiconductor substrate and the functionalization layer.

The heterostructure composed of the electrically insulating alkyl monolayer and the SiC as the substrate represents an ideal model to investigate the influence of the interface dipole layer and of the changes in the HOMO-LUMO gap (highest occupied molecular orbital - lowest unoccupied molecular orbital) of the grafted molecule on charge carrier transport across the interface as well as to compare the electrical quality of the alkyl layer to that of thermal oxides.

Publications