The dielectric constant of GaP from a refined analysis of donor-acceptor pair luminescence, and the deviation of the pair energy from the coulomb law

Abstract

It is shown that, by using computer simulated spectra, the fine structure observed in donor- acceptor pair luminescence can be analysed up to large pair distances R. For GaP, R is about 70 Å. Results of an application of this analysis to new accurate measurements on O P-C P and S P-C P pairs are presented. From the spectra involving the deep donor O p, the static dielectric constant ϵ is calculated to be 11.02 ± 0.05 at 1.6 °K. This value of ϵ can account for the experimental R dependence of the O P-C P pair energy, as calculated from the Coulomb interaction in the pairs, for R ⪆ 17 Å. The deviation of pair energy from the Coulomb law is determined for O P-C P as well as for the shallow S P-C P pairs. For short distances the energy of O P-C P pairs is larger than calculated from the Coulomb law, contrary to the finding for shallow pairs, for example S P-C P. The deviations from the Coulomb law for these pairs are discussed by considering a model due to Williams and Mehrkam and the van der Waals polarization energy. It is shown that the known treatments do not provide a satisfactorily theoretical explanation for these deviations. A theoretical approach along the lines of that of Williams and Mehrkam, but by taking full acount of polarization seems to be the most promising one. Finally, a new tabulation of donor and acceptor ionization energies is presented. It is partly based on the new data on ϵ, O P-C P and S P-C P pairs and, in addition, on S P-Zn Ga and S P-Cd Ga pairs.