Pore propagation directions in p(+) porous silicon

A comparative study is presented on the pore propagation directions of poro us silicon layers (PSL) formed on p(+)-type substrates of different orienta tions. PSLs were formed on plain (0 0 1) and (1 1 1) silicon wafers as well as on structured (0 0 1) wafers containing facets of various orientations. During anodization, regular pores follow the < 0 0 1 > direction on the (0 0 1) planes. While on the (1 1 1) planes fewer regular pores develop and s eemingly propagate closely to the < 1 1 1 > direction. These results indica te that the pores propagate perpendicular to the surface i.e. along the fie ld lines when the surface orientation is either (0 0 1) or (1 1 1). When the silicon surface provided (1 1 0) orientation (Chuang, Collins, and Smith, 1989), or its position is in between the (0 0 1) and (1 1 1) planes then the pores do not propagate perpendicular to the surface but along the < 0 0 1 > direction. All the phenomena exhibited might be explained by presuming that during for mation, the pores propagate along the < 1 0 0 > directions, and that those < 1 0 0 > directions are preferred which are closely to the field lines. In PSLs formed on (0 0 1) surfaces the field lines and the < 0 0 1 > crystall ographic direction are coincident. However, in the (1 1 1) oriented wafer w here three equally probable < 1 0 0 > directions exist around the field lin es, more irregular structure of PSLs will develop.