Fabrication And Characterization Of Nano-Porous Silicon Optical Waveguide Devices

Nanoporous silicon (PS) has become an ideal material for chemical and biological sensors because nanoporous silicon material has many advantages such as it has the extremely high surface area to volume ratio, and it exhibits strong adsorption of biological and chemical molecules, at the same time it is low toxic and compatible with biological tissue. It is suitable for integration and miniaturization with low fabrication cost.Up to now, the study on porous silicon was mainly focused on the bio-sensing and chemical sensing. The sensing principle of the nanoporous silicon optical sensor is based on the change of the porous silicon refractive index when the molecules are adsorbed into the porous silicon surface or when they are penetrated into the porous silicon apertures. Therefore, the study on the refractive index of porous silicon, structure and properties of nanoporous silicon has scientific significance to improve the sensitivity of nanoporous silicon optical sensors,In this thesis, nanoporous silicon was fabricated by electrochemical etching, and the nanoporous silicon refractive index was calculated based on the Bruggeman model and refractive index modified model of heavily doped silicon. The relations between the refractive index of nanoporous silicon and porosity, etching current density, etching time were investigated. At the same time, a Bragg mirror and a multilayer optical waveguide were fabricated, and the sensing properties of nanoporous silicon grating prepared using laser direct writing method was also investigated.1. We use Bruggeman model to calculate refractive index of nanoporous silicon, which was fabricated by electrochemical etching. The calculated result shows that the refractive index of the nanoporous silicon decreases linearly with increasing porosity and etching current density.2. The refractive index of nanoporous silicon was also measured by spectroscopic ellipsometry in the visible light spectrum range. The measured refractive index and extinction coefficient were in agreement with the calculated data, after being modified by the refractive index modified model of heavily doped silicon. In particular, we estimate the refractive index at the optical wavelengths in visible and near-infrared spectrum ranges, which may be widely used in various types of optical sensors and optoelectronic devices for optical communication systems.3. We fabricated the nanoporous silicon Bragg mirror which is periodic distribution based on the Bragg condition by electrochemical etching. And we also fabricated the multilayer nanoporous silicon optical waveguides. We do it all according to the tuning of nanoporous silicon refractive index by changing the etching current density.4. In order to study the sensing characteristics of nanoporous silicon grating, we use a nanoporous silicon grating, which is fabricated by the laser direct writing with a period of4μm and an air fill factor of30%, as a sensor. In the zero diffraction orders with incident angle of15°,16°,17°,18°, respectively, the change of reflected beam intensity was measured with different density of ethanol, methanol and acetone. It indicated that the strongest intensity occurred at incident angle of17°, the grating is most sensitive with the incident angle.