Fabrication Of Nanoporous Silicon By Electrochemical Etching For Optical Biosensors And Its Properties

Porous silicon material has extremely high surface area to volume ratio, and it exhibits strong adsorption of biological and chemical molecules. It is low toxic and compatible with biological tissue. It is suitable for integration and miniaturization. Because of simple and inexpensive fabrication techniques and other advantages, porous silicon (PS) becomes ideal material for chemical and biological sensors.Up to now, the study on PS was mainly focused on the fabrication, characterization of microstructures, analysis of chemical composition, luminescence mechanism, photoluminescence properties, and its applications. The micro structure of PS and its luminescence properties depend on the fabrication process and conditions. Therefore, the study on the fabrication process and properties of nanoporous silicon has scientific significance.In this dissertation, nanoporous silicon was fabricated by electrochemical etching. The surface topographies of PS, such as the shape of pores, the pore size, the thickness of PS layers, were characterized by SEM and profilometer. The effect of etching conditions on the surface topographies, the porosity, thickness, I-V characteristics, and refractive index of PS was investigated.1. The porosity of PS increased linearly with etching current density and etching time. The porosity of PS fabricated from low resistivity silicon(p:0.005-0.008Ω·cm) was higher than that from high resistivity silicon(p:0.01Ω·cm). We concluded that the porosity of PS was mainly related to etching current density and resistivity.2. The refractive index of PS decreased with the porosity of PS. On the basis of this relationship, we could fabricate different optical waveguide devices.3. The surface of PS showed well-distributed arborization structure, their pore diameters were about 15-25nm. The pore diameters of PS increased linearly with etching current density and time. But it was influenced mainly by etching current density.4. The thickness of PS increased linearly with etching current density and time. The thickness of PS fabricated from the low resistivity silicon(p:0.005-0.008Ω·cm)was higher than that from the high resistivity silicon(p:0.01Ω·cm). We concluded that the thickness of PS was mainly related to etching time and the resistivity.5. TheⅠ-Ⅴcharacteristics of PS had non-rectifying properties of Ohmic contacts. For the same etching time, the resistance decreased firstly and then increased with the etching current density. For the same etching current density, resistance increased with the etching time.