Design And Fabrication Of Porous Silicon Microcavities And Realization Of Multichannel System

Porous silicon is demonstrated to be a good platform to develop label- free optical biosensors of high sensitivity, attributing to its large surface area, variable surface chemistry and tunable optical parameters. In this thesis, a porous silicon-based one-dimensional bandgap photonic crystal structure is fabricated, which consists of upper and down Bragg mirrors, sandwiching a defect layer. The Bragg mirror comprises several periods of high and low porosity porous silicon layers, giving rise to a high reflectivity band in its spectrum. By inserting a defect layer in a Bragg mirror, a sharp resonance peak is introduced into the high reflectivity band. It is ultra-sensitive to refractive changes within the defect layer, which can be induced by infiltration of biomolecules, causing a shift of the peak. Based on this structure, the reflectivity changes are recorded against time, rather than the much used red-shift method. This technique is rarely employed to detect molecules in liquid form. The intensity-interrogated technique is proved useful to improve LOD (limit of detection) comparing to red-shift method (from 7×10-4RIU down to 7×10-5RIU). The sensing result is also found to be concerned with procedures the operator takes, which reveals the influence of adsorption and diffusion on the recorded signals. The design and realization of multichannel system is discussed in the last part.