Ultrathin semiconductor superabsorbers from the visible to the near infrared

En col·laboració amb la Universitat de Barcelona (UB), la Universitat Autònoma de Barcelona (UAB)i l’Institut de Ciències Fotòniques (ICFO)The design of ultrathin semiconducting materials that achieve broadband absorption is a longsought-after goal of crucial importance for optoelectronic applications. To date, attempts to tackle this problem consisted either on the use of strong -- but narrowband – or broader --but moderate -- light trapping mechanisms. In this work, we present a strategy that achieves broadband optimal absorption in arbitrarily thin semiconductor materials for all energies above their bandgap. This stems from the strong interplay between Brewster modes, sustained by judiciously nanostructured thin semiconductors on metal films, and photonic crystal modes. We demonstrate broadband near-unity absorption in Ge ultrathin films that extend from the visible to the Ge bandgap in the near infrared and robust against angle of incidence variation. Our strategy follows an easy and scalable fabrication route enabled by soft nanoimprinting lithography, a technique that allows seamless integration in many optoelectronic fabrication procedures