Optical reflectivity studies of radiation-induced trace disorder in silicon

For the first time, the effect of randomly distributed volume defects, induced by fast neutrons, on the reflectivity spectrum of crystalline Si has been studied. Reflectivity ( R) measurements were performed at 300 K in the range 3.7–11 eV. The influence of surface preparation on the quality of an R spectrum was checked. Proper surface treatment allowed additional features to be revealed of the reflectivity spectrum. It has been found that neutron irradiation tends to reduce the reflectivity of Si similarly as ion implantation does. Analysis of the reflectivity drop (Δ R), considering the defect structure of neutron-irradiated Si, allowed a correlation between Δ R and the concentration of the main defect species to be found. Precise measurements of the Si lattice constant have shown no changes of the single-crystal structure after neutron irradiation. The paper proves a very high sensitivity of optical reflection spectroscopy to the trace perturbation of the single crystalline lattice of silicon.