A SECONDARY-ION MASS-SPECTROMETRY STUDY OF P(+) POROUS SILICON

Porous silicon layers formed on p(+) substrates were investigated by s econdary ion mass spectometry technique. It has been found for the fir st time that the dopant impurity (boron) does not escape from the poro us silicon (PS) layer during the anodization. Analysis of the boron ex cess in PS in relation to the crystalline substrate provides a means b y which to study the porosity depth distribution. The resistivity of t he PS layer has been observed to depend strongly on depth: in particul ar, in the high-porosity layers (50-65%) a relatively thin insulating sublayer (about 300 nm) is found to form at the surface. After anneali ng of the PS layers in an oxidizing atmosphere, the high-resistivity r egions disappear.