A secondary ion mass spectrometry study of p+ porous silicon

Porous silicon layers formed on p+ substrates were investigated by secondary ion mass spectrometry technique. It has been found for the first time that the dopant impurity (boron) does not escape from the porous silicon (PS) layer during the anodization. Analysis of the boron excess in PS in relation to the crystalline substrate provides a means by which to study the porosity depth distribution. The resistivity of the PS layer has been observed to depend strongly on depth: in particular, in the high-porosity layers (50-65%) a relatively thin insulating sublayer (about 300 nm) is found to form at the surface. After annealing of the PS layers in an oxidizing atmosphere, the high-resistivity regions disappear.