Internal Friction in Germanium and Silicon II: Oxygen Movement and Dislocation Damping

Measurements of the magnitude of electronic and oxygen impurity relaxation peaks in single crystal silicon yield values for the extrinsic carrier lifetime and the relative oxygen concentration, respectively. This method is used to study the production of recombination centres associated with oxygen impurity, and the internal precipitation of oxygen. Recombination centres are induced when oxygen-containing silicon is cooled rapidly from above 1000°C to 650°C, reducing the lifetime to less than 0.35 μsec, which then recovers at a rate which increases with successive heat treatments. Precipitation onto internal particles at 1025°C occurs in the order of 3 hours for 2.7 Ω cm aluminium-doped silicon, and considerably longer for a purer sample, indicating that aluminium acts as an efficient precipitation nucleus. A 2% plastic deformation of the aluminium-doped specimen does not greatly reduce the precipitation time. Analysis of the precipitation curve form indicates that stresses around the precipitate particles may be important in determining the precipitation rate. Dislocation relaxation produces a rise in internal friction at elevated temperatures, an activation energy of 1.1 ev in germanium and 1.5 ev in silicon being associated with the rise. In silicon and germanium specimens which have been plastically deformed by about 2% the process becomes dominant above 0.6 of the melting temperature. Undistorted (`as-grown') specimens show a rise at higher temperatures, which varies in magnitude between specimens, and which could be due to the same process as that in deformed specimens. Oxygen in silicon appears to inhibit the loss process. Experimental results are discussed in the light of three possible theories, and it is concluded that there is insufficient evidence to indicate which one is applicable.