Pressure dependence of deep electronic levels in semiconductors: The oxygen-vacancy pair (orAcenter) in silicon

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Abstract
A study of the pressure and temperature dependences of the electron thermal emission rate and capture cross section for the oxygen-vacancy (O-V) pair (or A center) deep level in n-type silicon is presented. The results allow characterization of the three important thermodynamic parameters, namely the Gibbs free energy, the enthalpy, and the entropy associated with electron emission from this level and their pressure dependences. Analysis of the results leads to the following highlights of the work. (1) There is a large breathing-mode lattice relaxation accompanying electron emission. The sign of this effect implies that the lattice relaxes inward (i.e., contracts) upon emission and outward (i.e., expands) upon capture. The sign is in agreement with the prediction of a model for the O-V pair defect based on EPR results but, as far as we know, the present results provide the first and only quantitative measure of this relaxation. (2) The energy of this level is not pinned to either the conduction- or valence-band edges. The level moves higher in the gap with pressure consistent with its expected antibonding character. (3) The electron-capture cross section is found to be essentially temperature and pressure independent. It is suggested that this result can be understood in terms of nonradiative electron capture by multiphonon emission.