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Abstract
The most common fabrication technique of porous silicon (PS) is electrochemical etching of a crystalline silicon wafer in a hydrofluoric (HF) acid‐based solution. The electrochemical process allows for precise control of the properties of PS such as thickness of the porous layer, porosity, and average pore diameter. The effect of HF concentration in the used electrolyte on physical and electronic properties of PS was studied by visual color observation, measuring nitrogen sorption isotherm, field emission type scanning electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. It was found that with decrease in HF concentration, the pore diameter increased. The PS sample with large pore diameter, that is, smaller nanocrystalline size of Si between the pores, was found to lead to a pronounced photoluminescence peak. The systematic rise of photoluminescence peak with increase of pore diameter and porosity of PS was attributed to quantum confinement. The changes in nanocrystalline porous silicon were also clearly observed by an asymmetric broadening and shift of the optical silicon phonons in Raman spectra. The change in electronic properties of PS with pore diameter suggests possibilities of use of PS material as a template for fundamental physics as well as an optical material for technological applications.
Highlights
Porous silicon (PS) has attracted great interest both from fundamental physics [1,2,3] point of view as well as its technological applications in biological and chemical sensors, light emitting diodes, microdevices, and photoelectric solar batteries [4,5,6,7,8]
The mesoporous silicon prepared with different concentrations of HF was characterized by nitrogen sorption isotherms, field emission-type scanning electron microscope, photoluminescence spectroscopy, and Raman spectroscopy
The pore diameter and porosity of mesoporous silicon were found to decrease with an increase of the HF concentration in the used etching electrolyte at constant applied current density
Summary
Porous silicon (PS) has attracted great interest both from fundamental physics [1,2,3] point of view as well as its technological applications in biological and chemical sensors, light emitting diodes, microdevices, and photoelectric solar batteries [4,5,6,7,8]. Depending on the etching parameters, for example, current density, HF concentration, substrate doping type, and level, the physical properties of PS can be varied [11]. The conditions for the formation of PS on all types of substrates in terms of current density and HF concentrations were reported by Zhang et al [16], where they have shown that the formation of PS occurring during anodization was found to be dependent on the nature of electrochemical reactions. Journal of Nanomaterials shown that the red color of PS changes to yellow color by increase in applied current density during etching and this change in color was attributed to quantum confinement effect in silicon nanocrystalline between the pores. To further explore the occurrence of PL in PS, we have systematically studied the quantum confinement effect in three different pore diameter PS samples. The systematic studies of different pore diameter PS was carried out by using the Brunnauer-Emmer-Teller model (BET) on nitrogen absorption/desorption isotherm, photoluminescence, scanning electron microscopy, and Raman spectroscopy
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