Structural and Optical Characterization of Electrochemically-etched Porous Silicon
Lorenzo P. Lopez Jr.b*, Maria Angela B. Faustinoa, Niel Gabriel E. Saplagioa,
Arvin I. Mabilanganb, Neil Irvin F. Cabellob, Rhona Olivia M. Gonzalesa,
Arnel A. Salvadorb, and Armando S. Somintaca,b
aMaterial Science and Engineering Program – College of Science,
University of the Philippines – Diliman, Quezon City, 1101 Philippines
bCondensed Matter Physics Laboratory, National Institute of Physics,
Diliman, Quezon City, 1101 Philippines
This study have investigated the structural and optical properties of porous silicon on silicon substrate and of free-standing porous silicon layers. Porous silicon samples were fabricated through electrochemical etching of boron doped silicon wafer in 12% HF solution. For pore formation, current densities of 1.875 mA/cm2, 5 mA/cm2, and 15 mA/cm2 were applied to vary the porosity of the samples. To lift the porous silicon layer off the silicon substrate, an abrupt increase to 31.25 mA/cm2 was supplied at the end of pore formation. The porosities were calculated using Bruggeman effective medium approximation yielding 37.08 %, 76.12%, and 89.25%. Broadening of Raman and x-ray diffraction peaks was observed with increasing porosity, and is attributed to the increase of strain/stress present in porous silicon. The absorbance was calculated from the reflectance and transmittance of the samples, and was found within the range of the full-width-at-half-maximum of the photoluminescence spectrum. Surface states model was used to explain the mechanism of visible luminescence of the porous silicon samples.
Porous silicon (pSi) is a sponge-like structure in the nanometric scale. It is formed through electrochemical etching of silicon (Si) wafer in hydrofluoric acid (HF) ethanoic solution. Some parameters that affect pSi formation are the electrolyte concentration, etching time, and current density. The porosity is dependent on the concentration and applied anodic current, and effective thickness on the etching time. At a critical current during electrochemical etching, electropolishing of the Si surface occurs where pSi is lifted off from the surface and is referred to as free-standing pSi (FS pSi) (Bisi et al. 2000; Sailor 2012). . . . . [DOWNLOAD FULL TEXT HERE]
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