Temperature dependence of excitonic Γc-Γv transition energies GaxIn1-xP crystals

The excitonic Gamma (c)-Gamma (v) transition energies of disordered GaxIn1-xP (x = 0.0, 0.52, 0.70, and 1.0) crystals have been measured by photoreflectance (PR) measurements at temperatures from 20 to 300 K. The photoluminescence (PL) peak energy at 20 K is found to be lower than the energy obtained from PR or photoluminescence excitation (PLE) spectra by about 6 meV. The temperature dependence of the transition energy is expressed by a function consisting of several terms, each of which represents the effect of the volume-thermal expansion or the electron-phonon interaction. It is found that the temperature-dependent decrease of the transition energy from the pure electronic transition energy is mainly caused by the electron-phonon interaction. The energy shift due to the electron-phonon interaction increases as the Gap mole fraction increases.