The strained lattice of porous Si studied by grazing incidence X-ray diffraction

It is shown, that contrary to the usual assumption there is an in-plane lattice expansion in the p-type porous Si layers. This expansion is considerable but much smaller than the perpendicular one. The large width of the rocking-curves (in theta-scale) is practically independent of the order of reflections, but depends strongly upon the information depth. Thus besides the size effect the contributions of inhomogeneous lateral strains and/or local rotations are not negligible. The strong effect of the slight tilt of lattice planes on the information depth of grazing incidence diffraction is discussed and demonstrated.