PUB - Publikationen an der Universität Bielefeld

Amorphous silicon (a-Si:H) and porous silicon (PS) allow the realization of novel optoelectronic devices based on silicon. Both in common is the low cost fabrication process and the integration possibility with silicon technology. Whereas the optoelectronic properties of a-Si:H can be adjusted by the process gas of the plasma enhanced chemical vapour deposition (PECVD) process, the refractive index of PS can be varied by the etching parameters. Amorphous silicon multi-layers optimized with regard to the bandgap and mu tau-(carrier mobility x lifetime) product can be used as color detectors. Changing the applied voltage of the sensor leads to a shift of the maximum of the response front blue, green to red. In this way, a single detector generates sequentially a RGB-signal without the need of optical filters. Three color detectors employed as two terminal devices are based on pin or nipin layer structures. They exhibit a good linearity and a dynamic range of more than 90 dB. The refractive index of PS depends strongly on ifs porosity and microstructure. These quantities can easily be controlled by the anodization current density applied during the formation process. Stacks of layers with different refractive indices can be formed by modulating the anodization current density. These effects allow the realization of passive optical components like interference filters, rugate filters, antireflectance coatings, waveguides, and diffraction gratings.