UV REFLECTIVITY OF GAN - THEORY AND EXPERIMENT

A synchrotron radiation and theoretical study of the UV reflectivity of wurtzite GaN films in the range 030 eV is presented. First-principles calculations of the reflectivity and related optical constants are reported and used to analyze the experimental results. The calculations are performed assuming the local-density approximation and using a muffin-tin orbital basis set. The calculated peak positions are found to be in good agreement with the experiment to within a few tenths of an eV except for a constant shift of 0.98 eV which simultaneously corrects the minimum band gap. This constant upward shift of the conduction bands of the Kohn-Sham eigenvalue band structure is in good agreement with a recently calculated self-energy gap correction of 0.95 eV. A discrepancy in absolute intensities increasing with increasing energy is found between theory and experiment, the origin of which is discussed. The imaginary part of the dielectric function 2() is decomposed into its most important interband contributions and the relation between the features in the optical response functions and the band structure is described. The transitions from the upper N 2p-like valence bands occur in the range 3.515 eV. The transitions from the rather localized Ga 3d and N 2s bands whose energy is expected to need additional self-energy corrections are presented separately. The spectrum of the transitions from Ga 3d is closely related to the Ga 4p-like density of states in the conduction band. © 1995 The American Physical Society.