Dielectric function of wurtzite GaN and AlN thin films

Measurements and calculations of the dielectric function of wurtzite GaN and AlN are presented. Spectroscopic ellipsometry was used to determine ϵ( ω) of thin film samples in the energy range from 3 to 9.8 eV. Calculations of ϵ( ω) for the bulk materials were performed within a first-principles electronic structure scheme that includes the electron–hole interaction. The agreement between experiment and theory is dramatically improved over the previous work, a result of improvements in both experimental technique and theoretical description. The predicted polarization dependence of the dielectric function of these materials exhibits features similar to that in other wurtzite structure materials.