{111} defects in 1-MeV-silicon-ion-implanted silicon

Rodlike defects with the [111] habit plane have been identified by electron microscopy, at a well-defined depth below the surface of silicon specimens subjected to a 1 MeV Si ion implantation (1 X 10(14) cm(-2) dose, followed by 900 degrees C annealing for 10 sec), and coexistent with defects on {311} habit planes. Energy minimization calculations using the Stillinger-Weber potential were carried out on a self-interstitial atomic configuration; the final relaxed atomic configuration consists of five- and eight-membered rings. Calculated images based on this atomic model match ''double-spacing'' experimental high-resolution electron microscopy images. The energy minimization calculation suggests a displacement vector of a [111]/10, perpendicular to the habit plane, for the {111} defect. Diffraction contrast experiments revealed that, in the present specimens, about a tenth of the rodlike defects have this displacement vector. The [111] defects were also observed using a 120-keV electron microscope, below the critical energy of 170 keV for generating Frenkel pairs in Si by electron irradiation. This indicates that the {111} defects can be generated by ion implantation and annealing.