In this work, we develop a generic DNA based sensing platform used for characterizing surface functionalization and detecting DNA hybridization. Silicon nitride cantilever sensors are fabricated with an integrated three-electrode system and integrated in a microfluidic chip. Cantilevers with gold electrodes are functionalized with thiol-modified single stranded DNA (ssDNA) probes to detect target DNA. During functionalization and hybridization, information related to nanomechanical changes on the surface are obtained by optical measurements of changes in cantilever deflection. Simultaneously, the process is monitored electrochemically. The results clearly indicate that the electrochemical cantilever sensor is very sensitive for detecting DNA hybridization at the cantilever surface.
We demonstrate that the modulated surface photovoltage spectroscopy (modulated SPS) technique can be applied to investigate interface states in the bandgap, i.e. interface passivation, of crystalline silicon coated with a downshift layer such as hydrogenated aluminum nitride with embedded terbium ions by suppressing straylight with a cut-off filter. Different hydrogen contents influence the surface photovoltage spectra at photon energies below the bandgap of crystalline silicon. Modulated SPS reveals that at higher hydrogen content there is a lower signal and, thus, a lower density of surface defect states. Our experiments show that modulated SPS can become a powerful tool for characterizing defect states at interfaces which cannot be easily studied by other methods.
Silicon nitride (SiN x ) and silicon oxide (SiO x ) grown with plasma-enhanced chemical vapor deposition are used to passivate the front-side of liquid-phase crystallized silicon (LPC-Si). The dielectric layer/LPC-Si interface is smooth and layers are well-defined as demonstrated with transmission electron microscopy. Using electron energy loss spectroscopy a thin silicon oxynitride is detected which is related to oxidation of the SiN x prior to the silicon deposition. The interface defect state density (D it ) and the effective fixed charge density (Q IL,eff ) are obtained from high-frequency capacitance-voltage measurements on developed metal-insulator-semiconductor structures based on SiO x /SiN x /LPC-Si and SiO x /SiN x /SiO x /LPC-Si sequences. Charge transfer across the SiN x /LPC-Si interface is observed which does not occur with the thin SiO x between SiN x and LPC-Si. The SiO x /SiN x /LPC-Si interface is characterized by Q IL,eff > 10 12 cm À2 and D it,MG >10 12 eV À1 cm À2 . With SiO x /SiN x /SiO x stack, both parameters are around one order of magnitude lower. Based on obtained Q IL,eff and D it (E) and capture cross sections for electrons and holes of σ n ¼ 10 À14 cm s À1 and σ p ¼ 10 À16 cm s À1 , respectively, a front-side surface recombination velocity in the range of 10 cm s À1 at both interfaces is determined using the extended Shockley-Read-Hall recombination model. Results indicate that field-effect passivation is strong, especially with SiO x /SiN x stack.
Terbium and ytterbium co-doped aluminum oxynitride thin films were grown onto silicon substrates using radiofrequency magnetron sputtering. Aluminum oxynitride samples doped with 4.6 at. % of Yb3+ and co-doped with 0.4 at. % of Tb3+ were obtained. The prepared samples were annealed from 150°C to 850°C in steps of 100°C. By using energy dispersive X-ray analysis we measured the sample composition and the doping concentration. The emission intensities at different annealing temperatures were characterized using photoluminescence measurements upon excitation at 325 nm. The 5D4 → 7F5 main transition of Tb3+ and the characteristic near infrared emission at 980 nm of Yb3+ were recorded. In order to study the luminescence behavior of the samples in terms of a down conversion process, we have plotted the integrated areas of the main transition peaks versus the annealing temperature.
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