Research On 1-D Biosensor With Defect State Photonic Crystal

Porous silicon is easily prepared into various optical biosensors because of its good biocompatibility and large specific surface area.When porous silicon is prepared into an optical biosensor,the porous silicon biosensor is applied to many fields such as military,food,medical,environmental monitoring and the like because of its sensitivity to changes in refractive index.Improving the sensitivity of porous silicon biosensors has been an issue that experts at home and abroad have been discussing.When using porous silicon microcavity biosensor to detect biological molecules,because of the influence of porous silicon pore size,it is difficult for biological molecules to enter the defect layer of the device,and the defect peak is difficult to move,thus affecting the sensitivity of the device.Therefore,new detection methods that can improve the sensitivity of porous silicon biosensors have attracted much attention.In this paper,the factors affecting the sensitivity of porous silicon microcavity devices and the realization conditions of porous silicon microcavities are investigated.The refractive index and extinction coefficient of porous silicon was measured by ellipsometry,which provided a theoretical basis for the design and preparation of porous silicon devices.The reflection spectrum of porous silicon microcavity devices is always different from the theoretically simulated device reflection spectrum,mainly because the researchers regard porous silicon as the ideal of no dispersion,no absorption and smoothness in the theoretical simulation.The material,in fact,porous silicon has dispersion,absorption,and at the same time the surface of the porous silicon is not smooth,there is a certain undulation height.In order to solve this problem,this paper has made a detailed study on the dispersion,absorption and surface undulation of porous silicon.In order to improve the quality factor of porous silicon folded microcavity devices by directly entering the defect layer of porous silicon folded microcavity devices,we customize different specifications of Bragg mirrors and assemble them with the defective layer porous silicon Bragg mirrors fabricated experimentally.The conditions for the realization of porous silicon folded microcavity devices are studied.The main work of this paper is as follows:1.The ellipsometer was used to measure the refractive index,extinction coefficient and thickness of the single-layer porous silicon prepared under two different experimental conditions with high sensitivity and no damage to the porous silicon surface.By measuring the refractive index and extinction coefficient of porous silicon,the relationship between dispersion and absorption of porous silicon was obtained.The measurement of the thickness of porous silicon provides a basis for the preparation of porous silicon devices.2.The effect of dispersion,absorption and surface fluctuation of porous silicon on porous silicon micro-cavity devices was studied in detail using the transfer matrix method.Dispersion will reduce the bandgap width of porous silicon micro-cavity devices,and absorption will reduce the reflectivity of porous silicon.Surface fluctuation mainly affects the reflectivity of the defect state of porous silicon micro-cavity devices.This study provides an idea for improving the sensitivity of porous silicon microcavity devices.3.The air gap appearing in the assembly of porous silicon folded microcavity devices is analyzed theoretically by using the transfer matrix method.The size of the air gap only affects the position and quality factor of the defect peak in the reflection spectrum of the porous silicon folded microcavity devices.Two kinds of Bragg reflectors with different parameters were customized and assembled with porous silicon Bragg reflector with the defect layer.