Heterostructures of wide bandgap semiconductors such as silicon carbide (SiC) or group-III nitrides are attracting increasing interest for applications in the field of chemical and biological sensing. These biocompatible materials are particularly promising due to the possibility of bandgap engineering using the different SiC polytypes or AlxGa1-xN alloys, which could allow to optimize the charge transfer between the semiconductor device and the functional layer. A basic requirement for semiconductor biosensors based on organic-semiconductor hybrid structures is the direct covalent attachment of functional organic layers to the semiconductor surface. In my Ph.D. thesis, I systematically study different routes to obtain such functional layers on SiC and AlGaN alloys, including the silanization and hydrosilylation processes.
As an example, the figure shows a schematic view of the wet-chemical silanization process with either octadecytrimethoxysilane (ODTMS) or aminopropyldiethoxymethylsilane (APDEMS). We find that ODTMS layers on SiC exhibit very good diode-like electrical behavior but hinder the attachment of more complex molecules due to their chemically inert methly end-groups. Therefore, amino-terminated APDEMS layers were used e.g. for the immobilization of fluorescence-labeled proteins via an intermediate crosslinking step. To reveal the successful attachment of the proteins in fluorescence microscopy, such layers can be micropatterned as also shown in the figure.
In contrast to silanization, the hydrosilylation process of alkenes was supposed to require initially H-terminated surfaces. However, we are able to attach alkene molecules also to hydroxylated substrates via an addition reaction and have recently demonstrated this by the immobilization of fluorescent labeled proteins to TFAAD-layers on hydroxylated SiC and GaN surfaces.
I greatfully acknowledge a Ph.D. fellowship from Universität Bayern e.V. and support by the CompInt graduate school.