Optical transitions via the deep O donor in GaP. II. Temperature dependence of cross sections

Abstract

A detailed experimental study of temperature dependence of optical cross sections for the GaP: O one-electron state for $Tl300$ K is presented. Broadening effects on the edge as well as temperature shift of the deep-level binding energy and spectral variations of the measured cross section with temperature are treated. In our purely optical data from bulk material the overall broadening of the edge for ${\ensuremath{\sigma}}_{p1}^{0}(h\ensuremath{\nu})$ and ${\ensuremath{\sigma}}_{n1}^{0}(h\ensuremath{\nu})$ is well explained (\ensuremath{\sim}15% accuracy) by absorption of configuration-coordinate phonon quanta in the optical transitions, apart from an anomalous behavior below 30 K. The 0.9-eV O level is nearly pinned to the valence band below 175 K ($\frac{\ensuremath{\Delta}{E}_{i}}{\ensuremath{\Delta}{E}_{g}}=0.90\ifmmode\pm\else\textpm\fi{}0.10$) while above this temperature $\frac{\ensuremath{\Delta}{E}_{i}}{\ensuremath{\Delta}{E}_{g}}$ seems to decrease gradually. The temperature-dependent spectral behavior of the cross sections seems to be due to the presence of two different levels related to the one-electron O state where the new level is situated 80\ifmmode\pm\else\textpm\fi{}20 meV above the previously established 0.9-eV level. The apparent temperature dependence of the part of the cross sections associated with the 0.9-eV level is described in terms of a thermal activation energy of 0.4 meV.