A specific trap level at 78 meV in undoped liquid encapsulated Czochralski grown GaAs–SI materials

In this paper we provided experimental evidence for the presence of a 78 meV trap which is specific of liquid encapsulated Czochralski grown semi-insulating GaAs. This trap gives rise to a well defined thermally stimulated current peak obeying a monomolecular recombination model and amendable to an accurate differential analysis. The Urbach parameter Ei/kTm is shown to lie well below the usual domain, as it was established for low temperature peaks. The deduced cross section is weak, whatever the polarity involved, and quite adapted to the case of a double acceptor. The thermal activation energy 78 meV is consistent with the optical transitions observed in absorption or photoluminescence whereas it looks different with the deep level transient spectroscopy or photo-induced transient spectroscopy or temperature dependant Hall results; this discrepancy is explained by the influence in these experiments of neighboring traps of larger cross section. Then it is confirmed that this 78-meV trap could originate in a well-defined lattice defect and plays a decisive role in the electrical equilibrium of the material.