Infrared studies of low temperature electron irradiated silicon containing germanium oxygen and carbon†

Abstract

Single crystal silicon containing various concentrations of germanium, oxygen, and carbon has been irradiated at 90 °K with 2.8 MeV electrons and the ensuing defects studied by infrared absorption measurements. We find that, in n-type silicon containing 3 × 10²⁰ Ge atoms/cm³, there is no 12μ absorption line (A-center) after a 90 °K electron irradiation. The A-centers appear only after annealing between 200 °K and 280 °K. It is therefore inferred that Ge in silicon acts as an efficient trap for vacancies at low temperatures, the trapped vacancies being released from the Ge-V centers by thermal activation in the 200 °K-280 °K range. These vacancies then migrate through the lattice and are trapped on oxygen atoms. On the other hand we find that the interaction between silicon interstitials and Ge atoms is very low. The 935 cm⁻¹ absorption line is unusually intense in our experiments. Results suggest that the defects (‘B-centers’) which produce this absorption line are the result of the interaction of the silicon interstitials with oxygen atoms. In the last part of the paper, we study the experimental results concerning the 921 cm⁻¹, 931 cm⁻¹, 959 cm⁻¹ and 966 cm⁻¹ absorption lines. They are found to be associated with defectcenters involving carbon atoms and are clearly found to be produced by silicon interstitials. On the other hand, experimental results suggest a fast diffusion of carbon, at 300 °K, in interstitial sites aside from any irradiation effect.