Study of atomic displacements in He+irradiated silicon and a silicon-germanium alloy, through rutherford scattering

The disorder created by He+ ions of 275 keV and 1610 keV in Si and in a Si-Ge alloy (0.6 per cent atomic Ge) has been studied at 295 and 85°K through the use of channeling and back scattering of these ions. The disorder is measured through the relative yield of back-scatter for the beam incident in <111> and <110> directions. In both crystals, the disorder is not linear with fluence, and shows a tendency to saturate. In many cases the disorder measured along <110> channels is larger than along <111> channels, which indicates a prevalence of ‘interstitial-type’ defects. However, there is no indication of the structure of the defects. Part of the disorder could be attributed to slight displacements of atoms in the strain field of radiation defects. The low temperature irradiations create more disorder than room temperature irradiations, and this excess disorder does not fully anneal at 120°C. In Si(Ge), the number of Si or Ge scatterers is close to the concentration ratio even at high fluences. This shows there is no preferential process by which Ge interacts with Si defects.