Crystal orientation dependence of alternating current photo-assisted (ACPEC) porous silicon for potential optoelectronic application

Porous silicon (PS) was successfully fabricated using an alternating current photo-assisted electrochemical etching (ACPEC) technique. This study aims to compare the effect of different crystal orientation of Si n(100) and n(111) on the structural and optical characteristics of the PS.

PS was fabricated using ACPEC etching with a current density of J = 10 mA/cm² and etching time of 30 min. The PS samples denoted by PS₁₀₀ and PS₁₁₁ were etched using HF-based solution under the illumination of an incandescent white light.

FESEM images showed that the porous structure of PS₁₀₀ was a uniform circular shape with higher density and porosity than PS₁₁₁. In addition, the AFM indicated that the surface roughness of porous n(100) was less than porous n(111). Raman spectra of the PS samples showed a stronger peak with FWHM of 4.211 cm⁻¹ and redshift of 1.093 cm⁻¹. High resolution X-ray diffraction revealed cubic Si phases in the PS samples with tensile strain for porous n(100) and compressive strain for porous n(111). Photoluminescence observation of porous n(100) and porous n(111) displayed significant visible emissions at 651.97 nm (Eg = 190eV) and 640.89 nm (Eg = 1.93 eV) which was because of the nano-structure size of silicon through the quantum confinement effect. The size of Si nanostructures was approximately 8 nm from a quantized state effective mass theory.

The work presented crystal orientation dependence of Si n(100) and n(111) for the formation of uniform and denser PS using new ACPEC technique for potential visible optoelectronic application. The ACPEC technique has effectively formed good structural and optical characteristics of PS.