A MICROSTRUCTURAL STUDY OF POROUS SILICON

Porous silicon (PS) films obtained from lightly and heavily doped p-type silicon have been investigated by transmission electron microscopy. Silicon crystallites with nanometric dimensions have been evidenced in both types of porous silicon layers. High resolution observations revealed lattice disorder even for low-porosity (65%) samples. Concerning PS layers obtained from lightly doped substrates, it is shown that increasing porosity leads to a crystallite size reduction and to the deterioration of the material crystallinity. When the porosity is increased up to a value of about 85%, silicon crystallites with a mean diameter of less than 3 nm and an amorphous phase are clearly imaged.