Elemental process of amorphization induced by electron irradiation in Si

Abstract

We recently found that amorphization is induced in Si by electron irradiation. Examining the amorphization systematically, we have established the diagram of steady states under electron irradiation, either amorphous Si $(a\ensuremath{-}\mathrm{Si})$ or crystalline Si $(c\ensuremath{-}\mathrm{Si})$ as a function of incident electron energy, electron dose, and irradiation temperature. Utilizing transmission electron microscopy, electron energy filtered diffraction and electron energy-loss spectroscopy, we have characterized the atomic structure, the electronic structure, and the thermal stability of $a\ensuremath{-}\mathrm{Si}$ induced by electron irradiation. Based on the experimental data, we have also concluded that the amorphization is caused by the accumulation of not point defects but small cascade damages. Analyzing the change in the intensity of halo diffraction rings during amorphization, we have clarified that the smallest cascade damage that contributes to amorphization includes only about four Si atoms. This presumably supports the amorphization mechanism that four self-interstitial atoms form the quasistable structure $I4$ in $c\ensuremath{-}\mathrm{Si}$ and it becomes an amorphous embryo.