Influence of applied current density on the nanostructural and light emitting properties of n-type porous silicon

Abstract

Effects of current density on nanostructure and light emitting properties of porous silicon (PS) samples were investigated by field emission scanning electron microscope (FE-SEM), gravimetric method, Raman and photoluminescence (PL) spectroscopy. FE-SEM images have shown that below 60 mA/cm 2 , macropore and mesopore arrays, exhibiting rough morphology, are formed together, whose pore diameter, pore depth and porosity are about 265-760 nm, 58-63 µm and 44-61%, respectively. However, PS samples prepared above 60 mA/cm 2 display smooth and straight macropore arrays, with pore diameter ranging from 900-1250 nm, porosity of 61-80% and pore depth between 63-69 µm. Raman analyses have shown that when the current density is increased from 10 mA/cm 2 to 100 mA/cm 2 , Raman peaks of PS samples shift to lower wavenumbers by comparison to crystalline silicon (c-Si). The highest Raman peak shift is found to be 3.2 cm −1 for PS sample, prepared at 90 mA/cm 2 , which has the smallest nanocrystallite size, about 5.2 nm. This sample also shows a pronounced PL, with the highest blue shifting, of about 12 nm. Nanocrystalline silicon, with the smallest nanocrystallite size, confirmed by our Raman analyses using microcrystal model (MCM), should be responsible for both the highest Raman peak shift and PL blue shift due to quantum confinement effect (QCE).

Effect of the synthesis conditions on the properties of Co embedded porous Si nanostructures

“…The peak at 615 cm −1 is due to "wagging" vibrations of Si-H bonds (TO + TA) [21]. The broad and intense band spanning the region from 900 to 1000 cm −1 is due to stretching modes of Si-OH bonds on the surface [13]. We did not observe a 480 cm −1 peak in the Raman spectra of all samples which indicates that there is no amorphous Si in the structure [22].…”

“…Five fundamental Raman bands of PSi are observed at the 301, 430, 515, 615, 970 cm −1 . Among these, 301 cm −1 and 515.5 cm −1 peaks are due to 2TA and TO phonon modes of Si [13]. The peak around 430 cm −1 observed in the Raman spectra of PSi and PSi/Co samples is related to a local Si phonon mode due to a compositional disorder and localization in the PSi matrix [20].…”

“…The average pore diameter in this PSi sample, which has a high porosity, is about 850 nm obtained from the SEM image. These pores can be classified as macropores [13]. The pores are straight, but pore walls have considerably rough morphologies.…”

“…On the other hand, for 30-and 60-min samples, the shape of the main TO peak of Si became more symmetric while its full width at half maximum (FWHM) decreased indicating no quantum confinement effect occurred in them. We have been also calculated size of the Si nanocrystallites of PSi/Co samples using Microcrystal Model based on the QCE [13]. The calculated size of nanocrystallites has been summarized in Table 1.…”

Preparation and Characterization of Electrochemically Deposited Cu2O/ZnO Heterojunctions on Porous Silicon

“…PSi layer was derived via anodization technique by using n-type silicon wafer with orientation of (100) and resistivity of 1–10 Ω cm as defined in recent works. ,, Sigma Aldrich supplied all of the chemicals utilized in this study. Two-step deposition was performed to obtain PSi/Cu 2 O/ZnO nanostructures.…”