Radial microstructure and optical properties of a porous silicon layer by pulse anodic etching

This paper investigates the radial refractive index and optical and physical thicknesses of porous silicon （PS） layers prepared by pulse etching by means of reflectance spectroscopy,photoluminescence spectroscopy and scanning electron microscopy（SEM）.The relationship between the radial refractive index and optical thickness of the PS sample and the position away from the etched centre along the radial direction has been analyzed in detail. With the position farther away from the etched centre,the SEM image shows that the physical thickness of the PS sample decreases slowly,whereas intensely decreases from 2.48 to 1.72μm near the edge at a distance of 58μm.Moreover,the radial refractive index increases,indicating that the porosity becomes smaller.Meanwhile,the reflectance spectra exhibit the less intense interference oscillations,which mean that the uniformity and interface smoothness of the PS layers become worse,and the envelope curves of photoluminescence spectra exhibit a trend of blue-shift,indicating a reduction in nanocrystal dimensions.The PS micro-cavity is prepared to study the radial optical properties of the PS layer,and the results verify that the uniformity and smoothness of the PS layer in the centre are better than those at the edge.