A study of the (222) “forbidden” reflection in germanium and silicon

The absolute X‐ray intensity of the (222) forbidden reflection is measured in single crystals of Ge and Si by using monochromatic CoKα radiation. The inclusion of multiple reflections in the measured intensity is avoided by a suitable choice of the azimuthal angle. The values of the structure factors F222, deduced from the experimental intensities, are 1.54 and 1.08 respectively for Si and Ge. The F222 value for Si is not significantly affected by mechanical damage or by fast neutron irradiation up to a dose of 3 × 1020 nvt at about 100 °C. Furthermore, a search for the (222) reflection of Si with neutron diffraction and for the (420) X‐ray reflection in Si crystals doped with boron yields negative results. These results do not agree with those of other authors on the increase in the intensity of the (222) reflection and on the appearance of (200) and (420) reflections in doped Ge and in neutron‐irradiated diamond and Ge crystals. Therefore, the “true” intensity of the (222) reflection does not appear to be appreciably affected by lattice defects, but it is due to scattering by electrons of the covalent bonds.