Electrochemical etching of porous silicon - DFT modeling

Based on quantum-chemical calculations, the reactions that can take place on hydrogenated silicon surfaces under the action of both negative and positive ionic complexes of aqueous solutions of HF were investigated. It is shown that there is a high energy barrier for the passage of the H -> F substitution reaction; therefore, electrochemical dissolution of silicon according to the classical scheme is unlikely. On the faces (100), (110) and at their intersection, a barrier-free reaction of direct fluorination of silicon can take place. The mechanism of the transition between different regimes of silicon etching, the dependence of the rate of electrochemical etching and pore size in porous silicon on the concentration of HF in the electrolyte, and the reasons for the difficulty of electrochemical etching of silicon near boron impurity atoms are explained.