A MICROSTRUCTURAL STUDY OF POROUS SILICON

Porous silicon (PS) films obtained from lightly and heavily doped p-ty pe silicon have been investigated by transmission electron microscopy. Silicon crystallites with nanometric dimensions have been evidenced i n both types of porous silicon layers. High resolution observations re vealed lattice disorder even for low-porosity (65%) samples. Concernin g PS layers obtained from lightly doped substrates, it is shown that i ncreasing porosity leads to a crystallite size reduction and to the de terioration of the material crystallinity. When the porosity is increa sed up to a value of about 85%, silicon crystallites with a mean diame ter of less than 3 nm and an amorphous phase are clearly imaged.