Influence of pyramids and inverted pyramids on silicon optical properties

In this paper, we present a detailed study on surface nanostructuration of <;100> oriented p-type Silicon using a Cu assisted chemical etching. Scanning Electron Microscopy was used to describe the evolution of the surface morphology and structures during etching. The results show that the formation of either pyramids or inverted pyramids is mainly dependant on the etching time. Well-defined large-scale homogeneous but locally irregular pyramid-like structures are obtained on the silicon surface with quasi-perfect shapes. AFM measurements show the sample surface roughness with 0.6 μm of pyramids height and 1.2 μm of inverted pyramids depth. Samples with inverted pyramid structures have a low reflectivity (12 %) compared to those with pyramid structures (18 %) in the wavelength range of 450-1000 nm The Tauc plots of the nanostructures confirm the excellent absorbance of the inverted pyramids in a large band in UV-Visible and IR. The nanostructures have a pseudo-direct gap behaviour with values of Egd of 2.60, 2.55, 2.65, 2.45 and 2.05 eVand indirect band gap (Egi) values of 1.10, 0.95, 0.95, 0.85 and 1.05 eV respectively for 10, 15, 30, 60 and 120 min etching time. The values of Urbach tail energy calculated using Urbach law 160, 77, 67, 40 and 67 meV are smaller than those found using Tauc plot (0.33, 0.32, 0.36, 0.25 and 0.34 eV).