Structural and optical properties of nanostructured porous silicon for ethanol gas sensing application

Porous Silicon (PS) layers were prepared by electrochemical etching in a single-tank cell on the surface of single-crystalline p-type (100) silicon wafers, using hydrofluoric acid (HF) and ethanol (C2H5OH) in the volume ratio of 1:2. The surface and cross-section morphologies of the PS were observed from images obtained using Scanning Electron Microscope (SEM). Likewise, the porosity of the PS sample was determined using the parameters obtained from SEM images by geometrical method. SEM images indicated that, the pores were surrounded by a thick columnar network of silicon walls. This porous silicon layer can be considered as a sponge like structure. The X-ray diffraction (XRD) pattern showed the growth of PS layer on silicon wafer and the grain size of the PS layer was found to be around 60.2 nm. The effective refractive index of porous silicon was calculated using Effective Medium Approximation (EMA) analysis. The optical properties of PS were investigated using Fourier Transform Infrared (FTIR) spectroscopy and Photoluminescence (PL). The surface chemical bonds of the PS were observed by FTIR and the band gap of the PS sample was obtained from PL spectra. The efficiency of ethanol gas sensing properties of PS was investigated at room temperature. The sensor was found to operate with maximum efficiency at a concentration of 100 ppm hence, this PS material can be used as an effective sensor element to detect ethanol vapour.