The effect of etchant composition on film structure during laser-assisted porous Si growth

The structure of porous silicon films created by laser-assisted etching in aqueous fluoride solutions is shown to depend on the solution composition a s well as the laser intensity. Simultaneous porous silicon growth and depos ition of hexafluorosilicates has been observed for K+, Rb+ and Cs+ containi ng solutions, whereas little to no deposition occurs in Na+ and NH4+ contai ning solutions. Pore size decreases with higher laser intensity and high re lative concentrations of HF to HF2-, while larger pores are formed at low l aser intensity and high relative concentrations of HF2- to HF.