Influence of ionic character on GaAs 1− xP x:N photoluminescence spectra

Abstract

The photoluminescence (PL) band Nx due to the recombinations of excitons bound to nitrogen in GaAs 1− x P x : N indirect gap compounds are broadened and shifted to lower energies compared to the density-of-states band ϱ( E). A theoretical model based on the adiabatic approximation is given. In this model, the relative displacement of the ions creates a polarization which modifies the ions vibration frequencies. The displacement of the equilibrium positions of the ions under the effect of the effective electrical field leads to the overlapping of the vibrational states. The transition probability of the exciton phonon system due to the interaction with electromagnetic field taken as time dependent perturbation is a sum of products of Poisson distributions and densities-of-states. The Poisson distribution is characterized by an exciton phonon coupling factor S i for each phonon type called Huang-Phys factor for electron phonon coupling. The PL spectra at 18 K of nitrogen bound excitons in GaAs 1− x P x : N for different compositions x, obtained with the excitation energy E = 2.54eV is fitted by the theoretical line shape expression calculated in the model. The S i factors are adjusting parameters. The theoretical curves reproduce the PL spectra with a good accuracy reaching 98%.