Cathodoluminescence (CL) from n-type porous silicon (PS) was studied u
sing a transmission electron microscope (TEM) equipped with the CL det
ection system. Two luminescence peaks at wavelengths of 660 nm and 420
nm were observed from a cross-sectional sample. The monochromatic CL
images clearly reveal the spatial distribution of these luminescences
along the depth direction; the 660 nm luminescence is mainly from near
the top surface of the PS layer and the 420 nm luminescence the inter
face between the PS layer and Si substrate. The increase of the 420 nm
luminescence intensity upon removal of the Si substrate suggests that
the excited carriers in the residual Si matrix of the PS take part in
the 420 nm luminescence.