Singularities of the dielectric function of InN in the region of a direct optical transition

The dispersion of the dielectric function of InN with the wurtzite structure in the frequency region near the fundamental energy gap has been analyzed with the inclusion of temperature and carrier density effects. The linearity of the electron spectrum in a wide energy range leads to a logarithmic singularity of the real part of the dielectric function, which is associated with the direct electronic transitions and, correspondingly, to an anomalously large dielectric constant. The imaginary part becomes constant above the absorption threshold. The values calculated without any free parameters are in good agreement with the experimental data and ab initio calculations.