<title>Optical reflectance characterization of silicon micromachined surfaces</title>

Abstract

Advanced solar cells and optical detection devices incorporate surface texturing to reduce reflection of the incident radiation and, thus, enhance optical absorption. Using micromachining techniques, three different silicon surfaces were fabricated, optically characterized, and analyzed in terms of their ability to reduce optical reflectance. The fabricated surfaces consisted of: randomly sized and spaced pyramids (RSSPs), deep vertical- wall grooves (DVWGs) and porous silicon (PS). Three regions of the optical spectrum were investigated: visible (500 - 900 nm), near-infrared (1.25 - 2.5 micrometers ), and mid-infrared (2.5 - 12.5 micrometers ). A highly-polished, single-crystal silicon wafer was used as a reference surface. The following results were experimentally determined. The RSSP surfaces decrease the reflectance by more than 69% over the entire measured spectrum. The DVWG surfaces reduce the reflectance by 85% in the visible region, 34% in the near-infrared range, and 14% over the mid-infrared wavelengths. Both thin (pore depths less than 1 micrometers ) and thick (pore depths greater than 5 micrometers ) PS surfaces were investigated. The thick PS revealed better results compared to the thin PS, demonstrating 91% reflectance reduction in the visible region, a 7% reduction in the near-infrared range, and 53% reduction over the mid-infrared wavelengths.