Fabrication of porous silicon based tunable distributed Bragg reflectors by anodic etching of irradiated silicon

Abstract

We report a study on the fabrication of tunable distributed Bragg reflectors (DBRs) by gamma/ion irradiation of Si and subsequent formation of porous silicon multilayers. Porous Si multilayers with 50 bilayers were designed to achieve high intensity of reflection. The reflection spectra appear to have a broad continuous band between 400 and 800nm with a distinct central wavelength corresponding to different wave reflectors. The central wavelength and the width of the stop band are found to decrease with increase in irradiation fluence. The Si samples irradiated with highest fluence of 2×1013ions/cm2 (100MeV Ag ions) and 60kGy (gamma) showed a central reflection at λ=476nm and 544nm respectively, in contrast to un-irradiated sample, where λ=635nm. The observed changes are attributed to the density of defects generated by gamma and ion irradiation in c-Si. These results suggest that the gamma irradiation is a convenient and alternative method to tune the central wavelength of reflection without creating high density of defects by high energy ion implantation. This study is expected to provide useful information for fabricating tunable wave reflectors for optical communication and other device applications.