Dielectric function models for describing the optical properties of hexagonal GaN

Several different models have been employed for modeling the dielectric function of hexagonal GaN in the range from 1 to 10 eV. Models are compared in terms of number of parameters required, intricacy of model equations, and possibility of accurate estimation of important physical parameters, such as energies of critical points and exciton binding energies. Shortcomings and advantages of each model are discussed in detail. Excellent agreement with the experimental data for GaN has been achieved with three of the investigated models. It has also been shown that an assumption of adjustable broadening instead of a purely Lorentzian one improves the agreement with the experimental data and enables elimination of excessive absorption below the gap which is inherent to the models with Lorentzian broadening.