Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
In this work, an innovative porous silicon structure was utilized as an effective antireflective layer for silicon solar cell construction. Silvaco technology computer aided design tools were used to construct the three structures of the porous silicon layers which were no porous, single porous, and double porous. Athena process simulator was used to create the non-porous silicon structure (as control device) and the single porous silicon structure, while the double porous structures were created at the n-type and p-type surfaces of the silicon solar cell by using the device editor (Devedit) tools. The three simulated structures were imported to the Atlas device simulator tools to simulate the current-voltage (I-V) characteristic and the spectral response of the solar cell. The simulation results of the three structures were compared with the fabrication results obtained by Ramizy et al. Finally, the efficiency extracted from the double porous solar cell is 9.55%, the single porous is 9.32%, and the no porous structure exhibited 4.83% efficiency. The double porous silicon solar cell showed an ability to effectively trapping the light collected in the solar cell and thereby improve the efficiency of the solar cell compared to the no porous and the single porous silicon structure.
This paper investigates the effects of different etching techniques between direct current electrochemical etching (DCPEC) and integrated pulsed electrochemical etching (iPEC) on the structural and optical characteristics of porous silicon formation. The n-type Si (100) was fabricated using both techniques in an electrolyte that consists of aqueous hydrofluoric acid (HF) and ethanol (C2H5OH) with a ratio of 1:4. An additional pulse cycle of 14 ms with Ton = 10 ms and T off = 4 ms was supplied for iPEC porous silicon sample. The finding from both samples showed that the pore formation was affected by the etching techniques used. The porous silicon etched by the DCPEC technique produced a square-like pore with a porosity of 40% while the iPEC technique formed a mix of square and crossed shape pore with a porosity of 52%. From atomic force microscopy, the sample prepared by DCPEC was identified to have a deeper pore that causes larger crystallite size and better intensity in the Raman and photoluminescence spectra. On the other hand, the iPEC technique produced a higher and larger value of surface porosity and pore diameter but it has a shallower pore. The photoluminescence peak corresponding to red emission (S-band) is observed at 642 and 637 nm for DCPEC and iPEC samples, respectively. This is due to the nanoscaled size of silicon through the quantum confinement effect that was estimated to be around 7.9 nm and 7.8 nm for DCPEC and iPEC samples, respectively, determined from the quantized state effective mass theory.
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