## 3 Results and Discussion  
### Morphology  
It is imperative to note that the morphology of electrochemically etched PSi layers is highly reliant on the fabrication parameters, such as anodization current density, temperature, and HF concentration, among others. Here, we investigate an additional parameter that reveals diverse changes in the silicon surface structure,namely the cathode type. The new cathode configuration and the conventional Pt cathode configuration applied to three different substrate (silicon with different doping levels) to check the global and specific changes in the PSi samples in both setups. Comparison between PSi samples prepared on teh suface of S1 substrate using the Pt and Si electrodes are shown in Figure 2, highlighting the morphology and homogeneity of the nanostructured PSi layer. As portrayed in Figure 2b for the Pt cathode case the pore size appears to be smaller than those in Figure 2d for the symmetric silicon cathode case. The size of PSi in this sample is quite small, therefore, further analysis of size and distribution is difficult and will not be accurate. More reasonable analysis for size distribution is performed on sample with larger pores size to provide quantitative analysis for pore size and distribution. The first samples S1 reveals in both setups a nanoporous silicon surface (see Figure 2) with quite small pore size in the range of 20-40 nm. It is worth noting that this type of heavily doped silicon is used in photodetectors, then nanoporous surface maybe benefit to confine light at short wavelengths at nanoscale. Although silicon cathode has a higher resistivity when compared with Pt, these images show the successful fabrication of PSi layers using both configurations. The next step is to check the effect of substrate type and electrolyte on the fabricated sample. In each step, we maintain consistent fabrication conditions across  
Figure 2: Nanoporous structure on substrate S1 using (**a**,**b**) Pt cathode and (**c**,**d**) Si cathode. both setups for the purpose of comparison. While additional fabrication sets could reveal a range of diverse structures and morphologies, the three selected cases are sufficient to introduce the concept and examine the effects of the Si cathode type. A quite interesting microstructure surface obtained for the silicon samples S2, namely microflakes and spongy structures (see Figure 3). At large scales (tens of microns) the surface of the sample produced using the Pt electrode looks as a sponge with randomly distributed large holes as in Figure 3a, once we down to the nanoscale a clear spongy surface appears with tiny holes of few nanometers (see Figure 3b,c). Different from this case, the sample produced with the symmetric Si cathode show a surface with microflakes on top as we can see in Figure 3d. At the nanoscale, a spongy surface is visible beneath the microflakes (see Figure 3e,f), resulting in a bilayer surface structure. Although both samples show some uniformity at the microscale, they appear quite random at the nanoscale. In general, porous silicon (PSi) is effective at trapping light, which leads to a reduction in reflectance [36]. Certainly, this microflake structure will lead to a further reduction in reflectivity, as confirmed in the final section of the optical characterization. A comprehensive analysis of the pore size distribution was conducted for the samples fabricated on S3 substrate. The average pore size of these samples is approximately one micron, making it clear and straightforward to analyze. We used image] software (version 1.54g) to count the pore size and distribution in a total analysis area of 44 \(\times\) 31 = 1396.11 \(\upmu\)m\({}^{2}\). The SEM image and their pore size distribution are shown in Figure 4. In Figure 4b, the pore size show a wide plateau and high dispersion in size of image in Figure 4a, indicating low uniformity. The total holes area 316.011 \(\upmu\)m\({}^{2}\), this reveals porosity of 22.6% with total number of holes as 707 mostly distributed in a plateau between 330-950 nm.