Wideband mid infrared absorber using surface doped black silicon

Black silicon (BSi) is a synthetic nanomaterial with high aspect ratio nano protrusions inducing several interesting properties such as very large absorptivity of incident radiation. We have recently shown that heavily doping the BSi in volume enables to significantly enhance its mid infrared and tune spectral range interest up 20 micrometer. In present letter, we explore effect surface on radiative it absorptance, particular since reaching even larger dopant concentrations than but at more limited penetration depths. considered 12 different wafers BSi, fabricated cryogenic plasma etching n p-type doped using ion-implantation types, dosages ion beam energies leading profiles. The properties, reflectance, transmittance are measured Fourier transform spectroscopy. show an n-type wafer Phosphorous dose 10^17 atm/cm2 energy 100 keV increases 98% 1-5 propose simple phenomenological explanation observed results based concentration profiles corresponding radiation depth. Obtained provide design rules pave way for ion-implanted various applications solar harvesting, thermo-photovoltaics sensing where both absorptance variable required.