A center, in plastically deformed material, was here labelled SDX and was investigated by using deep-level transient spectroscopic, thermally stimulated capacitance, photo-capacitance and Hall effect methods. One feature of the center was a thermally activated electron capture with an activation energy of 0.30eV. This was comparable with the electron-emission activation energy of 0.40eV. Another feature was an optical ionization energy (1.47eV), of the SDX center, which significantly exceeded the equilibrium electron binding energy of 0.1eV. The electron emission from SDX centers in an electric field was significantly weaker than was expected on the basis of the Poole-Frenkel effect. The concentration of the SDX centers, as measured by using capacitance spectroscopic and conductivity techniques, increased with increasing screw dislocation density. Exponential electron thermo-emission from the SDX center was found to be accompanied by a non-exponentiality of the electron capture. The capture kinetics were fitted by using several models. The best agreement with the data was obtained for a model which assumed randomly distributed barrier heights. A model was proposed, for the origin of the SDX centers, according to which the SDX center was a non-effective-mass-state (DX level) of a shallow substitutional donor such as Al. In as-grown samples, it could not be occupied because it was appreciably above the Fermi level. In plastically deformed samples, the DX level moved down to the Fermi level (under the influence of the elastic lattice distortions around dislocations) and became detectable.

A.A.Istratov, O.F.Vyvenko: Journal of Applied Physics, 1996, 80[8], 4400-10