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Hydrogen dilution of silane during the rf-PECVD growth of a-Si:H absorber layers is used to suppress light-induced degradation of a-Si:H solar cells. The increased stability of cells and films deposited using hydrogen dilution is verified in an accelerated degradation experiment. At higher hydrogen dilutions the early phase transition to the microcrystalline phase complicates the growth of fully amorphous films as absorbers with a sufficient thickness. In a systematic study on the influence of various deposition conditions on the material properties the pressure is identified as an important factor for controlling the structural phase evolution of the films.

Two novel principles of sensing chemical concentrations by integrated optical sensors are presented. Both sensors are of the refractive type implying that a change of chemical concentration manifests itself as a change of the refractive index of a material located within the field profile of a guided mode. In contrast to common practice it is not the induced change of the effective refractive index N eff , but the change of the modal field profiles that is utilized for sensing, and here the changes of the refractive index finally show up as changes of the attenuation of a propagating mode. In the segmented waveguide sensor (SWS) the dependence of the modal transfer at the transition between two adjacent channel segments on the refractive index distributions of both segments is exploited while the second one relies on changes of the modal absorption as a result of a change of the penetration of the modal field into an absorptive region. Sensitivity and resolution-potential of both principles have been analyzed theoretically also taking into account the properties of peripheral equipment. Based on structures producible with SiON technology a SWS with a refractive index resolution of 5×10-7 can be easily designed. In an implementation of the second principle suited for immuno-sensing, a resolution in the thickness of the immuno-layer better than 10-4 nm is shown to be theoretically feasible. A SWS sensor has been realized; theoretically and experimentally obtained performance corresponds well to each other.

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Phone: þ420 377 634 732, Fax: þ420 377 634 702 A systematic and detailed analysis of the influence of hydrogen (H 2 ) dilution of silane (SiH 4 ) on the structural properties of thin hydrogenated silicon (Si:H) films was carried out. The Si:H films were prepared by plasma enhanced chemical vapour deposition method at different H 2 to SiH 4 flow ratios (R) ranging from R ¼ 0 to 40. A detailed structural analysis was carried out by X-ray diffraction (XRD). In order to suppress the XRD intensity from the substrate, Si:H films were deposited onto a [100]-oriented single-crystalline silicon substrate and XRD was carried out with a thin-film attachment. The XRD analysis demonstrated that the first diffraction peak in the Si:H films corresponded to the signal from silicon hydride (Si 4 H) ordered domains having tetragonal lattice structure. The full width of half maximum (FWHM) of the peak was decreasing with increasing H 2 dilution, and remained nearly constant for R ! 20. The FWHM values confirmed that the Si:H films grown at R ! 20 are more ordered than films deposited at lower R. This trend was confirmed by the Raman spectroscopy from the analysis of the shift of the Raman amorphous peak.