QUASI-OMNIDIRECTIONAL ANTI-REFLECTIVE STRUCTURE BASED ON POROUS SILICON DIELECTRIC MULTILAYERS FOR THE NEAR INFRARED, VISIBLE AND MIDDLE ULTRAVIOLET REGION OF THE ELECTROMAGNETIC SPECTRUM

摘要

The invention relates to an antireflective structure based on porous silicon multilayers stacked in a one-dimensional manner. This layer can reflect less than 4% of incident light at any angle, i.e. it is not dependent on the position in which it is oriented. This is achieved for a wavelength range from 200 nm to 2000 nm and with a total physical thickness of only 510 nm. The structure comprises 51 layers having gradual porosity values ranging from 92 to 38 %. The length of each layer is constant and equal to 10 nm and the profile of the refractive index varies by means of a monotonically increasing envelope function of the form f(z)=n₀+(n_F-n₀)(z/L)^k,with z the depth of the layer. The device is made using electrochemical anodization in an electrolytic solution of hydrofluoric acid and ethanol, attacking silicon wafers in a galvanostatic manner in a controlled interface.