Kubelka-Munk function, Urbach energy and Kramer–Kronig method in porous silicon

Abstract

Porous silicon (PS) samples were fabricated using electrochemical etching and characterized by atomic force microscopy, which showed that the surface roughness increases with porosity. The optical properties and the influence of porosity were investigated through specular and diffuse reflectance, transmission, and absorption measurements. Analysis of the diffuse reflectance spectra using the Kubelka–Munk function revealed that the optical band gap widens as porosity increases, indicating modifications in the electronic structure due to pore formation. The Urbach energy, determined from the absorption edge, also increases with porosity as a result of the higher density of unsaturated surface bonds. The dielectric constant, calculated via the Kramers–Kronig method, shows an increase in both its real and imaginary components with higher porosity, confirming the enhanced energy-storage capability of PS. Thermal energy-loss values likewise rise with pore content. Overall, the results demonstrate that increasing porosity significantly alters the optical and dielectric properties of porous silicon, supporting its potential applications in optoelectroni and energy-storage devices.