Heavy ion damage in silicon and germanium

Abstract

High resolution transmission electron microscopy techniques have been used to obtain information on the contrast, spatial distribution, size and annealing behaviour of the damaged regions produced within individual collision cascades by heavy ion bombardment of Si and Ge. Of particular interest was the dependence of the above features on the average deposited energy density θ ν within the collision cascade. Implants were performed at 35–50 K using monatomic and diatomic ions of 75 As, 121 Sb, 128 Te and 209 Bi, having incident energies of 10–120 keV, which meant that θ ν varied from 0.02 to 5.5 eV/atom. The bombarding ion fluences used covered the range 1.0 × 10 11 to 1.0 × 10 13 ions cm −2 . At high energy densities (θ gn 1.0 eV/atom), the visible damage produced in the main cascade consisted of a single, isolated damaged region. With decreasing values of θ ν (i.e. increasing ion implant energies), there was an increasing tendency for multiple damaged regions to be produced within the main cascade. Also, the fraction of the theoretical cascade volume occupied by a heavily damaged region steadily increased as θ ν increased. For high energy implants, at ion fluences > 5 × 10 11 ions cm- 2 , additional regions appeared which had lighter contrast than the multiple damaged regions formed in the initial stages. It is proposed that as overlap of the individual cascades occurs, the damage level in the peripheral regions becomes great enough to produce diffraction contrast in more extensive regions of the cascades. The annealing behaviour of the various damaged regions was also investigated at temperatures ranging from 300 to 775 K.