Aqueous electrolyte system for porous silicon using electrochemical anodization

Electrochemical anodization on n-type silicon was performed with silicon as anode and platinum as cathode in a weak-acid aqueous electrolyte containing orthophosphoric acid and ammonium fluoride. Anodization was carried out in two different modes, i.e., potentiostatic and galvanostatic with the voltage and current density of 5-80 V and 10-50 mA/cm² respectively. Anodization time was varied from 5 min to 10 hours. Morphology of the anodized samples was studied using scanning electron microscopy (SEM), revealing the formation of pores with uniform distribution throughout the silicon substrate. The pore size and density were controllable by varying the anodization voltage and current. Results showed that, in a broad spectrum range of 400-1100 nm, the total reflectance (sum of diffused and specular reflectance) of the porous silicon was about 10% compared to >30% of the as-received silicon wafer. The porous silicon is promising for solar cell applications due to the low reflection loss.