Electroreflectance study of the effect of $\gamma$ radiation on the optical properties of epitaxial GaN films

Experimental data on the electroreflectance spectra of $\gamma$-irradiated epitaxial GaN films on sapphire are reported. The irradiation doses are 10$^5$–2 $\times$ 10$^6$ rad. The theoretical electroreflectance spectra calculated on the basis of a model of three types of transitions are in agreement with experimental data with reasonable accuracy. The energies and broadenings of the transitions derived in the context of the model give grounds to infer that, in the GaN films, there are internal stresses dependent on the $\gamma$-irradiation dose.