The temperature dependence of vibronic spectra in irradiated silicon

Abstract

Crucible grown and high purity floating zone silicon specimens have been irradiated at room temperature with gamma rays. High resolution cathodoluminescence spectra of the vibronic bands with zero phonon lines at 0.717, 0.724, 0.790, 0.795, 0.898 and 0.969 eV are given. The widths and energies of these lines, and the intensities of the 0.790, 0.795 and 0.969 eV lines relative to the total intensities of their associated bands, are given in the temperature range 25 to 75 K. These data are discussed in terms of the theory of linear and quadratic electron-phonon coupling in the adiabatic approximation, using Debye spectra of coupled phonons and, for the 0.790, 0.795 and 0.969 eV lines, densities of coupled phonons derived from the emission band shapes. The theory gives a selfconsistency between the spectral band shapes and the widths and energies of the zero phonon lines, but does not satisfactorily fit the temperature dependence of the intensities of the zero phonon lines. It is not known whether the failure of the theory is due to a Jahn-Teller effect (no absorption at the centres has been detected), or to the coupling by the electron-phonon interaction of electronic states whose energies are not greatly separated compared with the phonon energies involved.