A High-Coverage Nanoparticle Monolayer for the Fabrication of a Subwavelength Structure on InP Substrates

Subwavelength structures (SWSs) were fabricated on the Indium Phosphide (InP) substrate by utilizing the confined convective self-assembly (CCSA) method followed by reactive ion etching (RIE). The surface condition of the InP substrate was changed by depositing a 30-nm-thick SiO₂ layer and subsequently treating the surface with O₂ plasma to achieve better surface coverage. The surface coverage of nanoparticle monolayer reached 90% by using O₂ plasma-treated SiO₂/InP substrate among three kinds of starting substrates such as the bare InP, SiO₂/InP and O₂ plasma-treated SiO₂/InP substrate. A nanoparticle monolayer consisting of polystyrene spheres with diameter of 300 nm was used as an etch mask for transferring a two-dimensional periodic pattern onto the InP substrate. The fabricated conical SWS with an aspect ratio of 1.25 on the O₂ plasma-treated SiO₂/InP substrate exhibited the lowest reflectance. The average reflectance of the conical SWS was 5.84% in a spectral range between 200 and 900 nm under the normal incident angle.