Crystal orientation and electrolyte dependence for macropore nucleation and stable growth on p-type Si

Macropore formation in moderately doped p-type Si was studied in mostly galvanostatic experiments (2–10 mA cm−2) with various fluoride containing electrolytes and substrate orientations [(100), (511), (5 5 12), (111)] from the nucleation phase to the phase of stable pore growth. Macropores on p-type Si always grow anisotropically in 〈100〉- and 〈113〉-directions. The most important parameter of the electrolyte is its ability to supply oxygen and hydrogen. Whereas oxygen is necessary for smoothing the pore tips, hydrogen is the decisive factor for the anisotropic growth and the passivation of macropore side walls. Based on a better theoretical understanding of the electrode processes in general pore formation in particular, etching conditions could be optimized for the generation of macropores in p-type Si with better aspect ratios, better stability, and smaller diameters than those in n-type Si.